How Do You Power Your Zenith T/O?
Using your Zenith Trans-Oceanic portable radio, in the way it was supposed to be used and enjoyed, is no longer an easy thing to do in the twenty-first century. Although the T/O has the ability to be run from the mains power grid - something that is easily and safely achieved, once the power supply circuitry has received the proper attention during restoration - it is not in the true spirit of the portable. If we wish to run our T/O as a true portable we must find a solution to the vexing issue of batteries.
The dual-voltage 9v/90v batteries went out of production in the late 1960's. Although zinc-carbon batteries are still available in 22.5, 45 and 67.5 volt types, they are very expensive and not a cost-effective solution to the problem of 'providing power'. Our radio is in need of two power supplies: a high tension 'B' supply, for the circuitry, and a low tension 'A' supply for the tube filaments ('valve heaters' in Brit.English).
The 9 Volt 'A' Supply
Achieving the 9 volts necessary is a simple matter of combining 'D' cells (or, indeed, any reasonable capacity 1.5 volt cell) in series. This is simple, low-cost and works well. The cell holders are easily available in a variety of configurations.
A Note Concerning The Dial Lamp of the 600 Series
The dial lamp for the 600 series T/O requires a 1.5 volt supply and gives a very feeble light. Why? Because Zenith specified a 2.2 volt bulb! Was this to keep the current draw low and lengthen battery life? Or was it to prevent loss of night vision when using the radio in the dark? Perhaps it was it to have a cold-running bulb to prevent damage or deterioration of the dial face? Who knows - maybe it was all three reasons. A better light source - but only if you are NOT interested in authenticity - is to use a 10mm white LED with a 180ohm resistor in series, powered from a 4.5 volt tap on the A battery. This gives a brighter, more useable light that will never need replacing.
The 90 Volt 'B' Supply
For the higher voltage 'B' supply, the simplest answer is to combine the required number of the small, square type 9v batteries in series. This may be done by wiring the snap leads together or snapping the batteries one to the other. The problem here, though, is that even if the cheapest type of battery is purchased (usually from an 'Everything For A Dollar/Pound' type store) one will spend a significant sum of money for a limited battery life. Bill Turner at dialcover.com has a presentable case with proper connectors for such a system. Most enthusiasts using this kind of set up claim between 30 and 50 hours battery life.
An alternative would be to use 60 'AA' cells to give us the 90V we need. Despite the daunting numbers of cells involved, it is an idea that can work well. A good sense of how well can be seen at www.batpack.com although this product is overpriced, in my opinion. Claimed life for sixty 'AA' cells is in excess of 400 hours at moderate use. The 10 cell 'AA' holders cost around US$2 each and batteries may be had for as little as 15 cents a piece and although this product is well finished, it would seem that one could build it oneself for a fraction of the cost.
In times past, there was an electromechanical device - called a 'vibrator' - that was capable of producing the high-voltage power required from a comparatively lower-power input. Usually, these devices were used in vehicle-powered equipment, most notably by the military, and although they were not terribly efficient they were fine when used with high-current supplies, such as those found in a car or truck.
Fortunately, there are now modern electronic equivalents of the vibrator that may be used with smaller, more common (and cheaper) cells such as the ubiquitous 'AA' or 'AAA'. Although these devices can be initially quite expensive, they pay for themselves over time by reduced battery replacement costs. Additionally, they may be more compact.
So far, I know of the following versions of the 'electronic battery'. I have used three of them and wish to discuss them here.
NEW ADDITIONS - March 2012!
- Although not commercial products, I direct the reader to Ronald Dekker's EXCELLENT webpage about the various iterations of the electronic battery that he has developed - It is very technical but well worth it!
- Also, Helge Fyske (LA6NCA, Larvik, Norway) has developed his own version of the electronic battery with an eye to powering his military sets. His webpage is here and a PDF of the project is here.
1. In the USA, Jim Poitivient trades on Ebay under the user name 'abbattery'.
His ready-to-use units are typically priced at US$95 each and use ten 'D' cells for both A and B supplies. I have had the opportunity to purchase one for close examination and use and, I can honestly say, they are impressive for the price. The whole system is housed in a red cardboard box that fits the T/O battery compartment exactly - as well as the T/O 'clones'. The rear of the box has a cutout for the battery plug - one may see the four pins within - and a small hole on the left side which can be used to pass the connector for the 600 series dial-light cell. Opening the box reveals the three 3-cell holders, the single cell holder for the dial-light, and a black box containing the inverter - these are all secured to a heavy, black-painted baseboard. I have opened up the inverter unit but Jim has heavily screened the electronics against RF interference and so nothing much may be seen.
In operation, this is the closest thing to having the real battery in terms of ease of use and battery replacement cost (disregarding the initial investment). Jim has produced a good, heavy, high-quality product at a reasonable price. Personally, I have wondered why he does not offer them through channels other than Ebay but I am sure he has his reasons. Jim may be reached at firstname.lastname@example.orgIn Arizona, Grand Canyon Tube Radio, appears to be selling a similar version of the ABBattery. They call it the 'Zenopac', it costs US$145, and it may be seen at their website
2. In Australia, Tony Maher, is an electronics engineer and vintage wireless enthusiast.He has contributed articles to 'Radio Waves', the journal of the Historic Radio Society of Australia, and has designed two types of 'electronic battery'. We will concern ourself with his design for the 'B' battery - and Tony's original article describing this unit (with parts list and schematic) can be seen by clicking HERE. Tony is able to supply the PCB and components for this unit, but the constructor will have to source their own case and battery holders.
Tony's design is a very compact power source that can produce 67 or 90 volts depending on the number of supply cells used. The whole unit is contained on a screen-printed PCB that only requires external connection to the supply cells. When in operation, there is no RF noise - surprisingly, there is no RF screening to this unit at all.
|3. In Germany, Hans Borngraber has developed an alternative that produces 11mA current at a variable voltage of 60-90V - using a 6v supply. Interestingly, Hans does not use a transformer to achieve this result. I found his page on a web trawl and provide a LINK to a translation of the article. I have emailed Herr Borngraber with questions but the messages are bounced back.|
4. In England, The Kit Radio Company 'KRC-A-2' was featured in 'Practical Wireless' magazine. It is a modern replacement for the British Ever Ready B126 90V battery and is supplied in kit form. It contains absolutely everything needed to build an 'electronic battery' that produces 85V from six 'AAA' cells. It can also be supplied ready-built but this is a little more expensive.
This is a solid and well designed unit, but there is no option to vary the output voltage by adding or subtracting supply cells. Although this isn't strictly necessary I believe that the 85V output may be a touch low for weak or marginal tubes.
In operation, the KRC-A-2 is completely silent and there was little RF noise across the standard medium waveband (the 'broadcast band'). The kit is supplied with a flattened case of heavy cardboard, printed with the original Ever Ready artwork - this is a nice touch and a good finish to a solid product.
The kit may be purchased from:
Tony may be reached at (44) 01959 563023 and KRC's website is at http://www.kitradioco/uk.htm