The Peter Wieck Notes

Care & Feeding of The Zenith T/O

Peter Wieck is a ZTO enthusiast who contributes on a regular basis to the Yahoo Groups forum for this ever-popular radio, as well as on Usenet at This is a collection of his advice, musings, wisdom and tips from the last few years and is presented with his permission and blessing.

I find that spring-steel is better, something from a worn-out pen clip such as the Stabilo line or any of several similar work well. It is a little tougher to cut, but a Dremel tool and small vise do the trick nicely - also for squaring and smoothing the ends. They are about the same width, and the "knuckle" at the end of it can often be bent out to duplicate the original hook shape.

I have also fabricated entire tips from proper-diameter wooden dowel cut to length, filed to shape and then epoxy-painted to the appropriate color (to match a leather T/O for example). I then drill in a bit of brass tubing, and thread it with a tap. The same Dremel set in the press and very fine drill-bits makes the slot for the
clip, a touch of epoxy glue and it will pass the three-foot test (or better) easily.

One more trick with the left over dowel: Sand the tip into a short, sharp point (>) that is maybe 10 degrees sharper than the typical knob-bright from the H and 600-series. Purchase soft, shiny hobby-brass which is easily cut or punched into "coins" of the correct diameter. Contact-glue these coins to a piece of rubber tire or some
such thick, medium hard resilient surface, center the dowel on it and give it a swift tap with a rubber mallet - instant knob-bright after a very short bit of practice. Once one has the knack the process is fast and easy - and cheap.

The Cam that lifts the red flag on the 7G, 8G and G500 series that is often missing or broken may be fabricated from hobby-plywood cut and filed to size, then sanded very smooth, then soaked in ultra-thin super-glue, allowed to cure, touch-up as needed with a file. The super-glue will make it very, very hard and resistant to wear. A touch of lithium grease on the wearing edge will make the action nice and smooth as well. Other similar parts may be made in the same way.

The little red tips for the 7G wave rod may be made from "Pop-It" bracelet/necklace pieces - they come in multiple colors and styles as well. File off the male end and polish with 600-grit paper. It fits right onto the tip metal tip.

A bit of a PITA, but the often-missing wave magnet extension cord may be fabricated from standard clear 300-ohm twin lead, punched with a ticket punch and colored with red Sharpie. Note that only two of the three end-pieces are active. That may be fabricated from a bit of the same hobby-plywood noted above, some thin brass tubing filed smooth at the exposed end, the twin-lead soldered into the two active leads, which are in turn super-glued to the bit of plywood. The red cover may be made from a bit of red plastic from any of many sources including red plastic bottles, plastic coffee containers and so forth. The snaps at the other end are readily available from Sewing Notions stores, fabricate the end piece from the same red plastic as sourced above.

SMALL cracks in faceplates may be almost disappeared by taping the "good" side with Scotch Magic Tape (accept no substitutes) and then using ultra-thin super glue (Zap-brand, accept no substitutes) by capillary action into the crack. Allow to cure for at least 24 hours before removing the tape. Do not shake, vibrate or move the
piece once the glue is in place. It will cure almost clear as the styrene if allowed to do so. If it is vibrated or bumped hard, a thin white line will result.

AND - upon receipt of any H500 or 600-series T/O, ALWAYS loosen the screws securing the faceplate at least 1/4 turn 'from snug'. This will prevent cracking from starting in the first place.

Loose, flaking paint and/or silk-screened numbers may be secured in-place using KRYLON (accept no substitutes) "Workable Fixatif" in several very light but thorough coats.

Note that the alignment diagrams on the Zenith schematics are upside down. They expected the alignment-tech would be working from the bottom of the radio with the chassis inside the case. On this subject, alignment tools with a small metal tip will will not affect the results.

If you intend to use the radio with a battery, align with the metal plate as suggested by Zenith. If you DO NOT intend to use a battery, align it WITHOUT the metal plate. That metal plate may be an aluminum pie-plate cut to size or some aluminum foil around a piece of cardboard for all the difference the material makes. It is the RF
shielding/reflecting properties at issue, not magnetic properties.

It is VERY important that your signal generator be accurate within a few percent for best alignment. So, do verify that using a digital receiver *IF POSSIBLE*.

I will lay out what I do and at the levels I do it. They are varied, and sometimes the same radio will take several processes.

A. For small holes (less than 1/4" x 1/4" (7mm x 7mm):
  1. I will gather shreds and bits of stag from corners and folds and tuck them into the hole in the way that seems best, fitting it (dry) first. An X-Acto does nicely for lifting the existing stag around the hole for tacking purposes.
  2. Then I use either an X-Acto or nail scissors to trim the hole clean, but not too clean. Just any long fibers or snotters depending on the stag type.
  3. Then I use a cheap soft artist's brush and *FABRIC CEMENT* ) the "goop") from any good fabric & findings source, dabbed around the hole and under the edges.
  4. Fit the salvage piece into the hole, oriented per the test. 
  5. Weight it with a soft surface and some weight. I will typically use a bit of soft thin foam rubber and a 6V gel battery I use for other purposes. Put a piece of plastic wrap over the patch, then the weight. Allow to dry.
  6. When dry (not long), a bit of 200/400 grit sandpaper and a light touch will "feather" the edges and break the shiny surface of the glue.
  7. Fabric dye will take dye quite well.

B. For larger areas but where entire recovering is not desired or not
necessary or not possible:

From your local hobby shop, obtain _BLACK_ Model Airplane Dope (flat) and _BLACK_ Airplane fabric. Here is one maker: There are many. It comes in various finishes, flat and gloss, woven and non-woven, film or fabric. It is best to GO LOOK as you are hunting for the texture that is closest to what you have or want. There are also various fine-cloth canvas materials (use cotton or cotton-blend if you are going this way) that you can get from a fabric shop that will do as well.

Then proceed as with A, but using the Black Dope (and heat if the fabric is so-designed) to glue the fabric to the case. Feather as above. The dope and the fabric take dye well. Several coats of the dope will soak into the fabric and the existing stag. Feather as above. Dye.

I tested the above fabric procedure on a piece of pine to make sure that I had the technique down before diving into a radio. You will have to buy more than you need anyway, so it is good to get an idea of the results in advance.

As to liquid shoe polish, that is fine if done sparingly. I prefer to rub the dyed surface with a soft cloth as the dye is curing to get an even coat. Then something like an acrylic clear automotive-type polish to get the level of luster desired.

My only "release" agent is plastic wrap on the weights or clamps. Waxed paper if absolute flatness is required.

Permit me a small rant.

Although shoe-polish has been used on T/Os for many years, and I expect that 'back in the day', there were few alternatives. However, it should NEVER be used today on any T/O, even the leather 600-series.
  • It does make a nice shine. But as it oxidizes, it flakes off. This is not so big a deal on your shoes, after all, you are walking on the ground and a few black flakes here and there are mostly meaningless and harmless. But not on your T/O where it will behave as black dandruff.
  • The stag fabric has little pores in the weave. Leather does not excepting suedes. Which, of course, illustrates the point: Would you put shoe-polish on suede?
So: There is black leather shoe dye:

There are any-of-several finishing products after that, from Armor-All (least desirable, but actually does a fair job) to various other compounds from automotive clear polymers and acrylics through a light coating of Model Airplane dope - flat through high-gloss, your choice.

And bad patches of stag can be repaired with any-of-several textured hobby papers and that same airplane dope, even sanded to feather into the existing stag. I have some patches that I defy anyone here to find, some as large as 3" square.

End rant... With apologies for it.

One Usenet contributor wrote:
"Peter, your well-known abhorrence of shoe understandable, but not an indictment of wax finishes in general. 
Properly applied, shoe  polish will not crack, chip, flake, stain your fingers or clothing, smell funny, or lose the war for the allies."

OK... I will go over my objections chapter & verse:
  1. Black Paste Shoe Wax (KIWI, Douglasville, PA) is made from Carbon Black, carnuba (organic) waxes, and several volatiles consisting of some fast-evaporating and slow evaporating hydrocarbon fractions. Can we agree on that?
  2. On shoes, automobiles and other items that use PIGMENTED waxes, when the wax wears out and fails, the detritus does not usually show in the local environment.
  3. Even then, most car waxes, furniture waxes and other applications where waxes are used as a protective finish, they are UNPIGMENTED.
  4. Stag is a textured finish, not a smooth finish as on the leather examples of the T/O. Therefore any finish applied will not be 100% even across the surface. More will (naturally) accumulate in the areas between the fibers than on the surface of the fibers. There is no way to avoid this natural difference in the depth of the applied finishes (assuming a paste wax).
  5. So, as the wax "dries", it will dry unevenly. This will cause uneven shrinking (witness dried mud) and therefore not a uniform finish either in depth or in adhesion.
  6. During the natural oxidation process, these differences will manifest in the surface shedding. Again, with shoes this is irrelevant.
  7. What is shed is a mixture of oxidized wax, carbon black and other bits accumulated during the process.
  8.  Note that with shoes, the old wax (polish) should be removed before new is applied... A rather difficult process (the second time) with a textured surface. And inevitably, organic waxes do oxidize.

Now, admittedly Armor-All (the worst functioning but best known of its ilk) does not give as momentarily gorgeous finish as properly applied paste-wax. At the same time when it ages it volatilizes entirely leaving no removal problems before touch-up. It does not shed. And it does not rub off, is not subject to softening when exposed to certain chemicals (including some skins sensitive (acidic sweat) to natural waxes), and it is far more forgiving of misapplication.

That about sums up my objections to shoe polish. As to the errors in "The Book", there are plenty including several "Frankenradios" represented as OEM, but none of them are surprising. What it does do very well is cover the basics of the breed, and most of the failings
are by way of dismissing or denying the existence of certain types and styles of these radios. And why we even know of these exceptions would be (in my opinion) because the book has created a most single-minded focus on these radios... dragging all the exceptions and peculiarities into the open.

5. ON THE 1L6
Well now you can get a SS replacement for every TO tube. Fine, if you are going to lug that big wooden box out to the boonies and you need a set of batteries to last a year. While yer at it, rig up a SS I'd tell you the two great sub-minis that work in the stead of a 1L6, but I'm afraid that you guys will suck 'em all outta' ebay before I can get me a couple more. I just want a few more, so that each one of my radios can have a real deal, a loctal, and a mini. You can figure it out pretty easily anyway; there weren't THAT many different readily-available sub-miniature tube types.

Miniatures: 1AC6, 1U6, DK-92(Euro)
Loctal: 1LC6, 1LA6 in an adaptor.
If you are lucky, a "hot" 1R5 will do as well. Sylvania (the only actual producer of the 1L6), it is rumored, would re-badge the 1L6 as a 1R5 on occasion depending on production demand. Consider that the 1L6 line ran both for civilian and military radios so this is not too terribly out of the question.

Note that a resistor parallel to the filament is suggested for the 1U6/1AC6 (for the DK92 it is suggested as well) drop-in replacements to reduce the demand on the filament circuit... especially if run from batteries. As I remember 50 ohms at 1/4 watt does it. The choices are to wire it under the chassis, or if _VERY_ careful to the actual filament pins and tack it to the tube itself with a bit of superglue. That makes the device a true drop-in.

Philosophically, I have no difficulty at all with SS stand-in replacements. When one is out in the boonies, a blown 50A1 or even a 3V4 can really ruin one's evening. Carrying spares is not always practical, and it is not as if one can drop into the local WalMart for replacements. The same applies "at home" where the idea is to receive signal and enjoy it, not have bragging rights of the "most authentic" radio. Save that for the meets and meetings.

The solid-state 1L6 is explained here:

It requires a full re-alignment afterwards.

Drop-in replacements include the 1U6 and the Euro DK92. Some have good luck with the 1AC6, and some very "hot" 1R5s are barely adequate. The 1U6 benefits from a small resistor added across its filaments. This may be done inboard or outboard.

There are plenty of 1L6s out there, it is just that there is a feeding-frenzy over them. Consider that there were nearly 500,000 Trans-Oceanics alone requiring them, not to mention the hundreds of thousands of clones also so-equipped. So there were countless millions of spares made not even including those made for the military. However, when they hit 'the market' they tend to get snapped up and hoarded. I have a much harder time finding a good 6A8G these days than a 1L6.

6. A 1L6 REDUX
With all due respect to the solid-state 1L6, there are several alternatives that do not require modification/realignment of the radio. These are in rank-order of ease:

1) A 1LA6 w/adaptor (also 1LD6 does nearly as well) Bill Turner will supply you with either in the proper adaptor (dial-cover@...)for a quite-reasonable price. Stock a few 1LA6s (a $4 tube), and you will be set for life. I keep two, and they are excellent, well-crafted performers.

2) Speak to one of your European buddies and try to find one-or-more DK92 tubes. These are "hot" drop-in replacements for the 1L6 and
require no realignment.

3) Screen a bunch of Sylvania, Tung-Sol or GE (NOT RCA or Philco) 1R5 tubes, if you have the time and the opportunity. I did so with about 10 of them, and got two that were as hot as any 1L6 I have including a couple of NIB versions. Note that the failures are still of value for testing and repair purposes, or if the radio is only to be used on the AM and lower SW bands.

All of the above options are considerably cheaper in cost than a 1L6, and cheaper in time and modification as well. "Nails on a chalkboard" is not the issue at all, but rather leaving the radio as original as possible, in the center of its performance design-curve, so to speak. I see the SS 1L6 as a viable option for those who will be in regions where tubes are simply NOT available, or for people who really do want to be once-and-done with it and use the radio on a daily basis.

I also am greatly appreciative to those who have had any part in developing this option, because sooner or later it will be the only one... and similarly for all the other tubes in the radio. But here and now, I see it as a last resort. I might consider making one as an exercise, but I would never realign a radio to accept it as long as I have viable alternatives.

7. ON THE 1L6 versus the 1R5
I have deleted all the leads to this post, but I want to clarify a few things as I have experienced them.

1. The 1R5 is not a drop-in replacement for the 1L6, so the pin-out and performance characteristics are somewhat different. BUT(!) it is a cheap tube and serves for all testing purposes with reference to miniature-tube T/Os. (drop-in replacements include the 1U6 and the European DK-92, both of which I have used successfully and without realignment being necessary).

1a. On the other hand, I have a few very "hot" 1R5s, coincidentally made by Sylvania, that perform just as well as any 1L6 in the inventory. Perhaps these are some of that legendary group of 1L6s relabeled as 1R5s when Sylvania had to fill an order. I am told that it happened.

2. The T/O was designed to operate on carbon-zinc batteries, making the filament voltage at 9.36V (6 x 1.56V) with new batteries, and then down as the batteries decayed. One of the things about batteries, is that unlike AC-based sources, they do not sag as much under load if the demand is within the chemical limits of the cell. AC sourced voltages therefore must be measured UNDER LOAD to determine the actual operational voltage.

3. Generally, I find that T/Os perform best at 8.4V across the string +0.6V/-0.2V. I try to run around 8.8V@117V at the receptacle, and calculate my resistances to suit. That is, unless I am worried about fluctuations in line-voltage. Then I clamp the string at 8.4V with a zener also reducing the size of the resistor. But I try NOT to go below 8.4V under any conditions as fade-out is common below that voltage.

4. The above voltages are measured UNDER LOAD... that is with the radio "ON" (and a 1R5 in place).

I wonder how many 1L6s have been trashed because individuals insist on running these radios at the absolute minimal voltages. I know from my direct experience that I have "rejuvenated" more than a few 1L6s that by description were "crapped out" just by feeding them a decent diet. Some few required their filaments to be shocked, but all of them came back eventually. I repeat my contention that I have never seen a 1L6 with an intact filament that could not be made to perform adequately in a properly set-up T/O. If the alternative is the trash, then what is there to lose in feeding the radio "design" voltage?

8. ON THE H500
A Contributor wrote:
 "I am glad you stay with the original tubes as that is more authentic. I also was looking at the H500 on ebay, but have no idea what they are really worth, either not restored, or restored. What is the price range on these radios? From what I read, at the time they were manufactured, they were considered high quality (This could be the reason they are still around?). Thank you."

The H500 was made from ~1951 through ~1959 although in very small numbers at the end of its run. Like most T/Os, it paralleled the 600-series at the end of the run as the 600 paralleled the Royal 1000 at the beginning of its run. (And, BTW, the last 600-series was made in 1963).

The price-range (and I can tell you that from the latest Kutztown Auction) is from $20 for a complete, restorable unit with a good faceplate to $150 for a fully-restored and pristine unit. I picked up a G500 for $20 at that auction that is "next" on my T/O queue.

Back in the day, they sold for something around $125 or so. Taking inflation into account (using the CPI), that would be the functional equivalent of $1260.00 today. Ouch! Approximately 250,000 H500s were made in all iterations (there are four (4) distinct iterations of which I am aware) including the military version. So, not only were they expensive at the time, but they were also sold by their many thousands. I would posit that the T/O tube series from 1942 to 1963 likely sold more than any other "Model" radio ever made, and any given model outsold its competition substantially until the end of the tube era.

So, Cost and Quantity would suggest that there will be a lot of them around. They store well and would not be thrown away in the same way as table-models or other consumer detritus of the same era. And I would guess as we (sadly) see the start of the pre-baby-boom
generation dying off in greatly increasing numbers we will see a lot more of them coming into the market.

Take your time and look for a good one (appearance).

As to the 1L6, they were made by the uncounted millions (and _ONLY_by Sylvania, by the way... all others are re-branded Sylvania production), and sold to the Military, Zenith, RCA, Stromberg Carlson, Hallicrafters, Capehart and countless other manufacturers over time. There are _MILLIONS_ of them out there as well as _MILLIONS_ of acceptable drop-in substitutes from the European DK-92
to the 1U6 to the 1AC6 and others. The so-called shortage is IMO due to Hoarder's Syndrome - I keep 8 @ 1L6, 6 @ 1U6, 4 @ DK92, 2 @ 1AC6 as one example. And these are spares, not counting those in active service. I also keep several of Bill Turner's adaptors. And, in 25 years of muddling about with T/Os and at least 300 crossing my path to one degree or another over that time, I have *never*, repeat,
*never* found a bad 1L6 with a good filament. And only two (2) actual, genuine, burnt-out 1L6s in that time. Of course, any number of radios with -no- 1L6 in them, but they do not count.

A Contributor wrote:
"The latches appear to be machine pressed and I doubt that you could open  then up without breaking them. I tried once and gave up doing more damage  than good."

Carroll is too modest and/or ran across a latch that had been "previously enjoyed" and therefore brittle.

a) The entire latch unscrews from the back. You will need to peel back the stag covering to remove the screws.
b) The top is stamped metal on a heavier metal base. If you are patient and have a pair of smooth-jaw pliers, you can work around the perimeter to remove the cover. Attempt to bend the least at the bottom as that is where deformations will affect opening and closing. You will get it apart.
c) if the bail (white-metal) is broken, you will usually find the cam-ends remaining inside the latch.

Now, I have done this twice, the first attempt passes a 5-foot test, the second passes even a close look if one forgives the 'square edges' on the bail. It is persnickety, but not impossible.

Obtain some brass hobby-stock at your local hobby shop. It should approximate the same dimensions as the bail. The first attempt I used round stock that I flattened to oval-stock after bending, but it got kinky at the bends. It is easier to use than rectangular stock, but rectangular stock looks better.

Cut a piece long enough to make the bail and to return into the latch by ~1/4" with a little left over.

Anneal the stock. Do this with a propane torch evenly along the entire length until red-hot. When hot dump it immediately into cold water.

Using either a bending jig or a vise with smooth jaws so that you can bend without kinking, make the bends. The brass should be quite soft, but if it starts to kink after part-bending, anneal it again as needed. You will be making two gentle bends and two pretty sharp ones. The second one I did, I notched the sharp bends (where the bail ends enter the latch) so that they could bend very tightly. When the bends are complete, the notches should be tightly closed. More on this later. If you used round-stock, anneal again and dap (flat-faced hammer) to an acceptable oval shape.

You should have a passable new bail at least in shape, that extends by ~1/4" each side into the latch.

File the stub-ends of the old pot-metal bail until they fit into the rectangular tube-stock or round stock, whichever you chose. Fit everything together and make sure that the dimensions are acceptable and work.

Take apart. Solder the bend notches with good solder, either 63/37 electronic solder or silver-bearing electronic solder. Get a little sloppy, the point is to make sure that the bends are filled.

Now, file smooth (#6-pitch jeweler's file) at the bends and then polish the bail using 0000 steel wool followed by brass wadding followed by Brasso). Spray with a couple of coats of clear lacquer.

Re-assemble, check alignment, and secure the stubs into the new bail with ZAP-brand (accept no substitutes) Gap-filling cyano-acrylate
glue. Be VERY careful not to slop this stuff. Use accelerator to cure if needed. A little bit of oil or grease on the backplate will prevent sticking if used carefully. Re-install the spring-clip and cover. Tap the flanges back in place CAREFULLY. A rubber dapping block or vise is most useful for holding the assembly.

Done. It almost takes longer to describe than to do with the right tools and after the first one.

One can ease the corners a bit on the square stock for a more authentic look, but not so much as to wear through.

A Contributor wrote:
"Hi all - Can someone suggest a supplier to order the diodes needed to  build the selenium rectifier replacement setup? Also, the proper diodes to order?  I am assuming that the same setup can be used in all the tube T/O's."

Mouser or Digikey. And/or R/S for any 200PIV 1A or-better silicon diode. 1N4007 is my favorite diode for replacement, but that is based on getting a couple of 60/$1 bags some time back. Otherwise it is a wee-bit overkill. Cheap insurance, however.

Be sure to add a 40 - 80 ohm @ 2 watts or better resistor in addition to the single diode to make up for both the voltage drop from the original selenium diode and for (typically) increased wall-plate voltage these days. 2 watts is also a bit of overkill, but also-and-again cheap insurance.

This new diode assembly will work for all the miniature-tube T/Os, but not for the tube-rectifier-types (7G & 8G).

Note also that the power-supply is always "HOT" as long as a T/O is plugged in. It is good practice to leave T/Os unplugged when not in
direct use.

A Contributor wrote:
"Forget all that nonsense. Get some dial cord from Antique Electronic Supply.  Go to their website and buy a roll. Costs about ten bucks for a spool and  their shipping time is fast. The dial cord choices they offer are first rate."

I do know about AES, which is precisely why I recommended the alternatives. For that same $10, one can get many yards of dacron fishing line in many weights, a dozen weights of rigging twine, and a thousand yards of nylon kite string. Oh, and the suturing needles.

The characteristics of dial cord are:
  •  No stretch
  • Abrasion resistance
  • Good knot-holding
  • Kink-resistance
  • At least some chemical resistance
Dacron fishing line has all of the above, comes in several weights and colors, and since it is not given an esoteric specialty label or from a specialty source, it runs pretty cheap. Since it is meant to be used and also primarily for salt-water applications, it meets all the requirements.

Rigging twine is designed for model ship rigging, so its resistance to stretch and knot-holding characteristics are excellent. It comes in many weights (and colors), but since it is something of a specialty item, it will be pricey as compared to the fishing line. But still cheaper than what AES sells, and one can "kick the tires" in the hobby shop before buying. Some of it has a wire core, excellent for those applications where there is considerable tension on the cord (such as in some audio tuners of the 60s and 70s).

Nylon kite string happens to be what readily available here in Saudi Arabia, and pre-stretching it takes care of its worst fault. For SR10 ($2.70), I got 200 meters of 200# test string. I pre-stretch it by hanging a section down a 3-floor stairwell with a 5 pound weight on the bottom... Being the "boss" helps when it comes to doing things like that. Let it sit for a week, and it is fine for use. So far, I have used a total of 8 meters... 92 to go.

One other reader of this group asked about "Tips and Tricks". One of the best tips one can give is _LOCAL_ sources for various materials necessary to the care and feeding of these radios. I am not against AES, at all. They are excellent for otherwise unobtainable parts. But the operating term is "otherwise unobtainable". Dial cord is one of the easiest things to find... as long as it is not dental floss.

A Contributor wrote:
"Hello Folks:  Just call me Total Neophyte! I have been both a SW  listener and an admirer of the Trans-Oceanic all my  life...but have never owned one. Now I think I may be ready to start!  I think that I admire most the 600 Series in the cowhide case, really beautiful and Pure Romance, but Totally Tubular!"

The leather 600-series is stunning, and they are good, reliable performers when properly house trained. I suppose that if I were to be somehow limited to one single unit it would be a hard choice between the 7G605 and the B600L in my collection. But they are rare, even
rarer in decent shape and tend to be overpriced. Some things to keep in mind that are unique to this unit:

a) The appearance parts are not interchangeable with any other model but this one. So that if the faceplate is or becomes cracked, or a knob is missing, or the antenna tip, flip-down door, wave-magnet, whatever, only another leather donor radio can provide a replacement.
Whereas with the stag models, a good many parts between even the 500 series and the 600 series may be interchanged.
b) The 600-series uses two expensive tubes, the 50A1 ballast (solid-state replacements for this are available) and the 1L6 (for which adaptors are available to the 1LA6/1LC6).

"AND, now 50 years-old and counting!  I would like to have one that I could listen to, rely on, use as a "daily driver"...Oh, but I forgot to  mention that I know very little about repairing these babies, (apart from what I have read about diodes and capacitors and a fuse modification at the on/off  etc...all of which frighten me even more"

Despite the fact that these are 7-band radios, electronically, they are nothing much more than an AA5(6) with a fancy antenna system strapped on. So, with a little bit of time and care, they are just as easily restored as the typical AA5, albeit a wee bit more complex. Diodes and fuse, recapping, all of that is easily done... again with a bit more time involved is all. Realignment takes about an hour if done carefully, but again is just "more" rather than "different". So, unless you are entirely a radio neophyte, there is nothing all that special about a T/O and nothing you will not have seen before.

"So, should I try to find one already already  "restored", or should I buy one and teach myself?  What have been your experiences?  If I find a "fixer-upper", are there certain items  that cannot be replaced, such as the antenna?"

These are two complicated questions: Speaking for myself, I would not rely on someone else's restoration unless I really knew them and their work. Questions of degree and philosophy are too many. On the other hand, there are many in this group whose work I would trust explicitly and implicitly, and a couple of (east coast) dealers similarly. But, for example, _ANY_ unit out of eBay (again unless from a known and reliable seller) I would assume to be either untouched at best or 'hacked' if called "restored"... but that is just my cynicism towards that venue.

I have gone over the appearance items. But keep in mind that NO appearance part of a T/O is available except from a donor radio. And
if you ever have to purchase parts of that nature, consider the cost of your vehicle if you were to buy it at the parts-counter. A complete T/O can be had at most East Coast swap-meets in the $30-$40 range (not pretty, but complete). The antenna alone may fetch that if sold separately. So, TRY to start with a complete radio or you will be chasing your tail for special parts.

Opinion Section:

Fuses and the T/O:
The miniature-tube series draws less than 10 watts in use. That would calculate to about a 1/10A dual-element fuse for its protection. At
120V, the actual draw is 0.084A, and the dual-element design will handle the starting surge. ANYTHING OTHER THAN A FUSE OF THIS NATURE WILL PROVIDE NO PROTECTION FOR THE RADIO. But a 1A fuse will protect your real-estate. So, you need to decide what it is you are trying to protect, the radio or your house.

What I would suggest is rather than fusing the radio itself, build a little fused receptacle (~$6 worth of parts at Home Depot) on an extension cord that will serve multiple radios just by changing the fuse rating. ALWAYS USE DUAL-ELEMENT FUSES (NOT, repeat NOT Slow-Blow fuses). Standard fast-blow fuses will fail constantly if of sufficiently low a rating to actually protect the radio, and provide
no protection at all if they do not fail constantly. Slow Blow fuses are worse than useless as they will permit the radio to operate at the edges of the fuse rating constantly, and well beyond the rating for short-but-potentially damaging periods. Dual-element fuses solve both problems very nicely. They can be rated VERY close to the ideal and still withstand the turn-on surge. Once on, the fuse will behave as a standard fast-blow.

Why Fusing Miniature-Tube T/Os is a good idea: The power-supply section is "hot" at all times. Best to leave them unplugged, but if one must leave them plugged in, then fuse them. ALWAYS.

Recapping a T/O (based on my experience):
7G605: Every cap, every time. These radios had all kinds of problems with their caps even factory-fresh. Zenith had not yet realized the
sorts of places these things would go and the abuses they would receive.
8G001 series: All electrolytics anyway. An excellent idea (almost necessary) to do all of the rest as well. The 8G is the MOST complicated T/O, but in my opinion the best performer within its bandwidth.
G500: Moving target. Mostly the electrolytics should be done. I have mixed results on the rest of the caps. One in my collection has 100%
OEM non-electrolytic caps. I took out a sampling for testing under load and voltage, they all passed with flying colors. Another needed
a total recap from end-to-end, all of the non-electrolytics had decided to become resistors.
H500: as above.
600-series: I have had only one that needed any caps, it had clearly been abused and water damaged, and so I believe to be exceptional in that regard. But your mileage may vary.

So, in general be prepared to do a total recap whatever the series. I don't shotgun my T/Os (except for the 7Gs and 8Gs) because I know
that as soon as they exhibit any signs of poor caps, they go to the bench immediately. For someone not "aways set up", shotgunning may be a viable choice towards reliability.

Common Problems to the T/O:
All series: Open/intermittent Candohm resistors. On the 7G, the upright square-ish metal box, all others under the chassis riveted to
the left side (from front) of the radio.
Dirty Band-switch: All bands go through the BC section, so if that section is dirty the radio will be silent. Similarly with the tone switches.
Poor contact on the battery change-over switch.
Poor contact on the headphone jack: When headphones are plugged in, the speaker is cut off.

Miniature Tube Series: In addition to the above, bad selenium diode. Replace it with a silicon diode and additional resistance. This additional resistance may be anything from 20ohms at one extreme to 80 ohms at the other. Much depends on your voltage at the wall-plate. Additional resistance is less necessary (unnecessary if on has a SS 50A1, or a large supply of same) for the 600 series. The ballast will take up the slack.
Open Sand Resistor: The sand resistor acts as a fusible link on the T/O. My opinion is that is by design, others may think differently.
Either way, open sand resistors are VERY Common. In the later-series H500s, this resistor is dual-section. If replaced with standard high-wattage resistors, a fuse becomes a VERY good idea.

Note that the later 600-series radios have the headphone jack on the front panel. If the jack leads are disconnected, the radio WILL NOT
PLAY as the speaker circuit goes through this jack. You will need to jumper the connection to align the chassis outside of the case, or
remove the jack from the case and leave it connected. Make sure that you get the leads in their correct positions.

A Contributor wrote:
"One thing I usually do with my antique radios,  including tube Zenith TCs, is make a fused extension cord. Here is  the recipe - get a new, good quality extension cord. Go to RS and  get an in-line fuse holder and a fuse - a 1/4 amp slo blow is ideal  [if not a regular 1/2 amp fuse will do"

OK, a couple of things (or more):

First, this is excellent advice in general. And adding a fuse to a system with the basic power-supply always "hot when plugged in" is definitely a good idea.

But: One should NEVER use a slow-blow fuse on any vintage radio ever! Here is why: Slow-blow fuses work on a function of time-over-rating, such that a small excess rating will take a very long time to blow the fuse, and as the rating is exceeded by a greater and greater amount, the fuse will blow faster and faster. Dead-shorts and it will behave just as a standard fuse, for example. But a few watts of excess and it may hang in as serious damage is done.

However, there is something called a "dual-element" fuse such as was used on the mil.spec. T/Os and others. These come in fractional values right down to 1/10A. What it does is handle inrush current nicely right up to perhaps as much as 10X the rating, but after the inrush is handled, it behaves as a fast-blow fuse should the rating be exceeded even by a little bit. Using these, one can tailor the fuse to exactly what is required.... and NO MORE, a very good thing.

One thing to note: D/E Fuses do not like being short-cycled. They need at least a few minutes to recover between cycles, or they will fail instantly at turn-on. Also a good thing if one thinks about it. And, they are (relatively) not cheap, but as they are unsurpassed at actually protecting the radio (and not just the real-estate), they are a sound investment.

As to the sand-filters they were Zenith's factory-fuse system, and typically, they do not fail due to rough handling as much as they are the reason that the radio was put aside in the first place. They are wire-wound resistors that behave much as fusible links if their current rating is exceeded for any length of time... such as bad caps or worse, and they were deliberately designed to fail before the candohm resistor, a not-cheap element to replace if it were to fail.

If one does replace the sand-filter (and some were tapped as well on the H500 series) with a standard resistor, one MUST install a fuse, as this basic protection would be gone.

Replacing the selenium diode is a good idea, but if one does so, one must install additional resistance to replace the internal resistance of the original diode. This is (really) less of an issue in the 600-series as the 50A1 will take up the slack, but not a bad idea in general to reduce the stress on the 50A1 if one worries about it. I typically do not on the 600-series and I have never lost a 50A1 (or a 1L6) even after years of heavy use. I do add about 50-70 ohms on the 500 series.

Otherwise, adding a fuse is a VERY GOOD THING, if the fuse is sized properly and one has a clear idea of what one is trying to achieve by it. 1/4A S/B will protect the real-estate but not so much the radio. Similarly with the 1/2A F/B. But a 1/10A D/E (about 12 watts) will
do both nicely. In areas of low line-voltage a 1/8A may be required.

Every so often, I put together the random bit and pieces I have picked up over the years. In no particular order:

1. Keep in mind that the T/O is essentially a gussied-up AA5 with a fancy antenna system. It ain't nohow a complicated radio past the coil tower. DO NOT be afraid of it! At the same time be exceedingly careful of the coil tower, wiring and surroundings. And, like an AA5, it can have a hot chassis, lethal voltages on exposed parts, all the rest. DO use an isolation transformer when working on these radios again just like any other AA5.

1a. The drawings on the Zenith-published schematic for aligning 500 and 600 series radios (for sure) are UPSIDE DOWN from when you view the chassis in the radio.

2. Use a 1R5 ILO a 1L6 when testing and troubleshooting the miniature-tube series.

3. Shoe Polish SHOULD NOT BE USED on stag. It flakes. Forever, once applied. Aniline Leather dye, two coats. Rubbed then with a soft lint-free rag. Then any number of additional coatings including Armor-All & its clones, 1:1 thinned model airplane dope (semi-gloss), Krylon (gloss) Fixitif (NOT lacquer), also polished after drying/curing with a soft cloth.

4. Leather gets a good soap from a tack-shop, and then a wax from the same source. Lexol comes to mind.

5. It is absolutely critical to measure current draw on a T/O, most especially if the selenium diode (on those that use them) is replaced. This takes a sensitive meter or other measuring device.

6. It is a fact that most T/Os were designed against either 110V or 115V at the wall-plate. Today, wall-plate voltages can vary up to 130V as power companies must deliver more and more current and are trying to avoid installing new infrastructure. This means higher primary voltages. Just keep this in mind when using these beasts. For the 7G and the 8G, this is less critical than for the miniatures.... and keep in mind that the 50A1 is approaching the 1L6 in cost.

7. Alignment should be done to the conditions that the radio is most likely to see in general use. When most of these were *actually used as* portable radios, aligning with a steel plate under the chassis was a good idea. But if the radio is not to be used with a battery today, it actually does make a difference if it is aligned without said plate.

8. And, speaking of the above, a good signal generator, that has been on long enough to stabilize before the alignment is begun is critical. Given that most of us use instruments of similar vintage to our radios, this bears repeating.

9. Clean band-switches are critical to the entire operation of the radio. Do not think that a single pass w/contact cleaner does the trick. Do the cleaning in several passes over several days. When spraying the cleaner, exercise the switches constantly, and for several seconds afterwards. Remember that ALL Signal goes through the BC switch, so pay special attention here.

10. Even some (actually quite a few) T/Os suffer from Silver-Mica disease. Obtain a cheap AA5 with miniature cans and practice cutting out the silver-mica caps at the base & replacing them w/100pf +/- outboard caps. You will need to at some time or other should you take on a later-version H500 or almost any 600-series. This appears to be micro-surgery, but actually the hardest part is getting the can off the chassis and keeping track of the connections in all the clutter. Do both if you do one. Symptoms are crackling and drifting that does not respond to recapping and/or alignment... also difficulty aligning, of course.

11. Something well over 600,000 tube-type T/Os were made between 1942 and 1963. They are NOT rare radios, although some of the group are rare relative to the whole. Please keep in mind that there are quite a few so-called "common" radios that were made in far fewer numbers than even the 7G605, but because of their style and interchangeability are not considered very valuable. I am all for radio-inflation at one level, however some of the prices I have seen for radios which survive in their hundreds of thousands are truly crazy. Of the T/Os, and *excluding* the two military versions, the rarest in my experience are, in order:

  • Leather 600's
  • H500 w/50A1 socket
  • 7G605 Sailboat
  • 7G605 Bomber
  • H500 w/adapted G500 chassis
  • 8G w/multi-voltage capacity
  • 600-series w/rear headphone jack
  • G500
  • All other 8Gs
  • H500 All versions except as above
  • All other 600-series

12. Cleanliness and a couple of good sealable containers are important when working on T/Os... containers for buttons, knobs, screws, spacers, antenna clips, suction-cups, cables, tubes, whatever when the chassis is out on the bench. Also a holder or accomodation on the bench to connect the waverod and wavemagnet to the radio in their proper relative positions for alingment is helpful.

13. Testing the reception on a T/O in the basement, or during the day is an exercise in frustration. Also in any sort of office building, around vast quantities of fluorescent lights and DD HVAC controls. They are simply too sensitive to operate properly in excessive RF clutter. Some modern heat-reflective glass (common here in the Kingdom of Saudi Arabia) has a very high iron or copper content as well. So, do not blame the radio if it is all-of-a-sudden uncooperative when asked to show off.

14. When recapping, patience and care are critical. Also placement. If the radio does not respond as expected after a recap, try moving some of the new caps around under the chassis. DO take a good photo (Polaroid or digital) of the "before" in enough detail that you can trace connections. Try shifting cap locations to match the photo if you run into post-capping performance problems. Check your work constantly. Best-yet, get someone else to check your work afterwards or wait at least 72 hours to check yourself. It is a fact that one will pass over the same error over and over if one is too "close" to the work.

15. It IS possible to repair the hair-thin coil wires. It takes a steady hand, a good magifying glass (or a HIGH-END magnifying lamp such as those made by LUXO) and the right tools (or a very sharp needle). Even the "under" end can be teased out of the coil with care and patience. Soldering also can be done with great care and a very fine tip to the iron. Just keep in mind that the coil is shot anyway unless you succeed.... so you do have nothing to loose! A bit of super-glue applied with a sharpened toothpick can steady your fragile repairs after the fact, also replace the varnish insulation.


First: Recapping
7G: ALL caps ALL the time. Don't waste your time or risk the radio by playing around, especially if you intend to use it on mains power. Pay attention to the Candohm resistor and antenna connections as well.

8G: All filter caps. Depending on the series, either all paper (non-electrolytic) caps, or be prepared to do all paper caps soon. If you intend to operate the radio regularly on mains power, do it now.

G500/early H500: (two-prong headphone jack): Moving target. If ANY cap is bad, do ALL the caps. Otherwise, if it aligns properly and there are no untoward noises, if the tone controls work as expected, it is OK to leave it alone as long as you do not play it unattended - and this is true of any radio of that vintage with an always-hot power supply irrespective of recapping.

600-series: Same as above, except that in most cases, it is enough to do the main 4-section filter can. I have very seldom found bad low-value caps in this series.

Next: Unexpected, Un-recognized and/or Un-discussed problems
a) Silver Mica Disease: Small-IF can units are prone to this. The silver in the caps at the base of the can migrates. The symptoms are thunder and lightening (crackles and pops) persistent and distracting, most prevelant on the BC band. A major PITA to correct, but can be corrected *WITHOUT* replacing the cans. They must be removed and opened, modified then reinstalled, however. Or, you can simply replace the cans. They are a standared 455 can, nothing special.

b) Bad selenium diode: Fer crissakes, replace the $%^&*, sad, silly thing and be done with it. Use the proper resistance for your location and intended use. If you are going to use the radio on a battery pack, and promise on your future grave never to use it on mains power, you may ignore this advice. Otherwise, just be prepared for a toxic, very bad, very persistent smell (weeks and weeks if it gets into the house heating system) and don't complain. After all, we told you so.

c) Poor reception on high bands: Did you also clean the tone switches as well as the coil tower? All signal goes through there too. Did you replace the diode? Are you getting the correct voltage through the filament string? And after 100% verifying all of the above, did you do the alignment?

d) Weak 1L6: in 27 years and perhaps 300 T/Os of one sort or another passing through my hands, I have _NEVER_ seen a bad 1L6 with a good filament. I am about at the point of believing that their ain't no such thing... either that, or I have to revise my position on the Loch Ness Monster, the Jersey Devil and Sasquatch.

e) Tube Rectifier Models (7G, 8G): If you are using an 8G or 7G with the 117Z6, check BOTH sections of the rectifier. If the 117Z3 in the later 8G, check it. I have seen A LOT of bad rectifiers - which for some reason persistently go untested.

f) YES, a 1LA6 or 1LC6 on the correct socket adaptor *IS* a drop-in replacement for the 1L6. Re-alignment will be minimal or not-at-all if a very slight displacement from the dial to the frequency can be tolerated.

Guys and gals, these are SIMPLE radios. They are nothing but a gussied up AA5 with a fancy antenna system attached. With minimal care-and-feeding they are excellent performers. With somewhat better care and feeding, they are as safe, reliable and rugged as any other AA5 radio of similar vintage, and much more so than many. They are MEANT to be carried about, and MEANT for a certain amount of rough treatment and rough conditions. They are NOT shrinking violets. Just don't slam them about when running - too much. And this for the same reason that one does not slam a hot light-bulb around - filaments break.

And, as I do in all of these rants: If you have a miniature-tube T/O, upon receipt, REMOVE the 1L6 and INSTALL a 1R5. Keep the 1R5 in place for *all* tests and basic adjustments. A decent 1R5 should get you excellent BC and the two lower SW bands anyway. If it cannot, you have other problems that must be solved first before you go running about blaming poor reception on a "weak" 1L6 and so forth. So, get with the program and get one-or-two 1R5s in the inventory. It remains a $3 tube for the most part. So getting a half-dozen in hand to cull out the hot ones is a good investment.

Urban Legend (with some real truth to it): Sylvania, the ONLY maker of the 1L6 (Yep, the ONLY one. ALL 1L6s of whatever brand were made by Sylvania) ran that line more-or-less continuously throughout 1L6 production history. When they had a surplus of them, they would relabel them as 1R5s. Really. The raw-cost per tube was so similar as to be of no concern. So, hunt down those Sylvania 1R5s - you might be looking at a "stealth" 1L6.

End Rant

16. Getting Started:

A few things about getting started in the vintage radio hobby – TransOceanics notwithstanding. Some of this is basic common sense, some of it is based on over 30 years in the hobby:

Electricity is no fun. It can hurt, it can kill, and it can injure in any number of ways not necessarily by shock. Sparks, heat, flashes and fire are only a few of those ways. Treat it with respect and you will be fine.

Even transformer- type radios can have a hot chassis. Those of you who are familiar with pre-war Zenith consoles will have very likely come across a slagged transformer or three – these beasts were notorious for them – and that can lead to a hot chassis.

AA5/6/8 (and 100% of all tube-type TransOceanics fall into this category) radios have a hot chassis when on. Many of them will have a hot chassis any time they are plugged in. As if it were a loaded gun – that level of respect must be accorded to every T/O.

Although these radios have lots of parts and a fancy coil tower and lots of switches, they are really not terribly complex in any way that should discourage anyone in taking one on. Sure, practice on a few `simpler' radios to get some basic techniques and process down and to understand what is going on – but if you can do everything up to and including an alignment on any given AA5, you will be fine on a T/O.

Equipment – Minimum Requirements:
Isolation Transformer: Although an isolation transformer will not protect anyone from outright stupidity, it will protect one against shocks from the chassis to otherwise grounds. If you are working in a basement on concrete, you will understand the issue completely.

Excellent Light: I keep three (3) articulated lights on my bench, one of which is a Luxo magnifier. Three separate sources gives me shadow-free light from about any angle.

Eye protection: Unless you wear rated glasses, hot sparks and molten metal in the eyes is no fun at all.

Good hand tools: All of mine are either US or German. And worth every penny.

Decent soldering tool(s). I keep an inexpensive soldering station (40-watts max) and a 38 watt pencil. They do nicely. I have a bulb desolderer, desoldering braid and a small piston desoldering tool. They have been adequate for many years. Although I admit to being jealous of those with vacuum pumps attached to a dedicated iron.

Good solder: There is nothing worse than crappy solder, solder with a wide liquid range and solder that is too thick.

Good VOM – invest in a good one. I bit the bullet 10 years ago and got a Fluke. I have never regretted that investment. And you will find it useful for many purposes outside the hobby.

Next Stage Equipment:
Signal Generator: Get a good one that is easy to use and that you can verify for accuracy. A digital AM/SW radio is useful for verification purposes.

Metered Variac: Unmetered Variacs are worse than useless. No further discussion is necessary on that point. Dim Bulb Testers are useful for gross diagnosis and so have their place if a metered Variac is not available. But they are not accurate enough for fine work.

Signal Tracer: When the signal *stops* , often you have found the problem. There are neat hand-held beasts available these days that will inject either AF or RF at whatever point you wish. Or, you can find an old-fashioned one at a swap-meet for $15 - $30 or so. Useful in any case.

ESR Meter: if you _MUST_ try to reform capacitors, and also useful for testing new caps before they are installed – what? you have never found a bad new one? It will happen.

Digital Camera and good color printer: Ideally one that can print `actual size' or larger. TransOceanics and their clones more-so than any other tube radios or even audio equipment are acutely sensitive to component placement. Moving a replacement cap even a few fractions of an inch or mm from its original position can cause all sorts of havoc. A digital camera can get you all sorts of pictures for placement – and in case you forget what was where it can save you. A large-format printer will give you good visuals for comparison. And you can mark up a piece of paper.

An oscilloscope can be a useful tool. In 30+ years I have needed one (1) time for vintage radio work. As I do not do FM alignments (yet), I have no regular use for one. When I retire, I will embark on that aspect of the hobby, however.

Tube Tester: Last and possibly least: For the record, an emissions-tester capable of testing for shorts and gas will be all you will ever need for 99-44/100ths of all radio-related tubes. Period. Unless you are matching tubes for audio use, there is _NO_ need whatsoever for a GM-type tester, much less a $1,200 Hickok. But the best test of any tube is in-situ, whatever the tester tells you. I keep a Simpson 555 and a Hickok 539B. The Hickok comes out twice a year for Kutztown for the most part. The Simpson gets used perhaps twice a month. I snagged the Simpson in excellent condition for $35. The Hickok was pure blind luck at $100 – even more-so as it was properly calibrated and had a solid-state 83 already installed. But the seller had three of them, was going out of business and I was one of his better customers (anyone remember Leon Fertik?). This was also more than 20 years ago – before the legend of the 539-series had driven prices to obscene levels.

After all that, take your time and enjoy.

Tell your significant other that radios:

a) Don't eat.
b) Keep you close to home.
c) Are much cheaper than another (woman/man).  

lLast update: 26th April 2012