El-tronics AE-30 Transmitter

El-tronics AE-30 Transmitter

The El-tronics AE-30 Transmitter cost $220 in 1948. Its output is 30 watts according to two ads placed in the 1948 QST magazine. According to the ads, the transmitter is a five band single dial gang-tuned band-switching transmitter. The 80, 40, 20, 15 and the 10/11 meter bands are covered. The final RF amp tube is an 807. Rectifiers are 5Z4 for bias, a 5Y3 for LV B+, and a pair of 816 mercury vapor rectifiers for HV B+. The large National ACN tuning dial is marked for each of the 5 bands covered. Apparently the tuning settings were hand calibrated for accuracy.

El-tronics AE-30 lighting a 40 watt dummy-load bulb
El-tronics Ad

El-tronics AE-30 advertisement.
El-tronics AdEl-tronics Ad2

Repairs
Overall, this transmitter was in good cosmetic condition. I noticed that power input as well as connection to a possible external modulator is by way of a rear panel-mounted barrier strip. That exposes not only the AC line but also the over 600 volt high B+ on screw terminals on the strip. Although such connections are typical on older rack mount devices, safety is of concern to me. I replaced the worn 2 wire power cord with a proper 3 wire grounded version. I then made a clear plastic cover for the barrier strip. In inspecting the transmitter further, I noticed that the 807 ceramic plate connector was not properly holding the plate cap. I replaced that ceramic connector with another one from the "boxe de junque". While there, I also placed some heat-shrink tubing around the plate choke. I don't like having high voltage that can be easily touched. A little heat shrink tubing goes a long way to improved safety.

Early signs of life
After further safety checks and careful cleaning, the transmitter was powered up without the rectifiers in order to check the transformer AC voltages at the rectifier sockets. The transmitter has a three position power switch including the "OFF" position. The first "ON" position is just for the lower B+. A third position is for the highest voltage by way of mercury vapor rectifiers. Satisfied with transformer voltages, I powered the unit up slowly with just the bias and low B+ rectifiers. Using a hand-held frequency counter, I found that the transmitter's oscillator, buffer and driver were indeed pumping out RF at or very near the tuning dial indications.

The transmitter uses a pair of 816 mercury vapor rectifiers. Per the instructions in the manual, I allowed the mercury vapor rectifers to heat for about 15 minutes to vaporize any elemental mercury that may have been spilled onto the tube elements during movement to my QTH. This extended pre-heating is a one-time event according to the manual. After the transmitter is in place, no special pre-heating is necessary.

Mercury vapor rectifiers in El-tronics AE-30.
Hg vapor rectifiers

The blue glow
I connected a 40 watt dummy load bulb to the antenna terminals before turning on the transmitter. I turned the power switch to the third position. The mercury vapor rectifers emitted a characteristic pretty blue glow but the dummy load bulb did not light. The current draw of the 807 was also low according to the meter. Checking the plate voltage of the 807 at the modulation terminals on the rear-panel barrier strip showed about 900 volts, much more than the roughly 650 volts I had expected. I began to suspect that the screen voltage might not be adequate. Shutting off power, I checked the screen circuit. I found no continuity on the large adjustable chassis-mount bleeder resistor that is tapped for the screen supply. Without that resistor, the chokes would not have a proper minimal load, thus explaining why the final plate voltage had gone very high. The screen supply would also be zero, thus explaining the low current draw and no RF output.

Replacing that big resistor
The rather large bleeder resistor is a 50 watt 25000 ohm with an adjustable tap. I did not have a replacement but the "boxe de junque" yielded some ten-watt 5000 ohm resistors. I selected four fixed and one adjustable 5000 ohm units, mounted several terminal strips on a scrap aluminum plate and drilled holes in the plate to match the mounting bolt holes left by the original resistor. The resistors were wired in series to make up a total of 25000 ohms at 50 watts. The screen tap was supplied by the one adjustable resistor. Tube manual specs for the 807 had provided the information for the approximate point for the tap. The result was a successful repair. Upon power-up, the dummy load bulb now glowed at roughly the expected RF output and the plate current could be set at the proper dip which was on the mark for 4 of the 5 bands. The 80 meter band needed a bit of tweaking.

El-tronics AE-30
El-tronics Ad

Performance
Although large and heavy as expected for a proper rack-mount transmitter or exciter of the 1940s, the El-tronics AE-30 is simple to use. A lot of care went into the design. The components are all quality. VR tubes are used to stabilize the lower B+ voltages. The capacitors are nearly all mica. The highest voltage filter caps are rated at 1000 volts and are not electrolytic. While there is no provision for crystal control, none is needed. The tuning is surprisingly accurate except for some variation at the very top of each band. I suspect a slight tweaking of the trimmer caps will solve that problem.

A rare transmitter
The AE-30 is a very rare transmitter. I found only one reference to it on the web and that was for someone wanting a picture for a publication. Why so rare? The El-tronics schematic is dated December 1946. The transmitter was not available until 1948. El-tronics was an unknown company to hams in 1948. The transmitter was likely their only ham product. Only two ads were placed in QST for March and April 1948. The price of $220 was also quite high in 1948, equivalent to over $2000 today.

From the design date in December 1946 to its Spring 1948 introduction a big change happened for hams, the era of cheap surplus equipment. An ARC-5 transmitter and a home-brew power supply was much cheaper with twice the power output of the AE-30. This was also the beginning of concerns about television interference. The link-coupled output of the AE-30 was likely a problem for TVI. Competition included Johnson's Viking 1 kit the following year for slightly less money but with lots more power and a built-in plate modulator (but less tubes or VFO). The Viking was heavily advertised and from a known company. For these and probably other reasons, the El-tronics Corporation turned to other projects.

Viking 1 Ad.

The El-tronics Corporation
El-tronics became known for the manufacture of Geiger counters for uranium prospecting and for Civil Defense. In the 1960s, its mainstay was lighting products. Assuming it is the same company, it later became known for the manufacture of medical devices.

While rare, a serial number of 1078 implies some others exist. Let me know if you have an AE-30. I have both the schematic and manual and can make a copy available to other owners. My thanks to KB8JLG for thinking of me as a good home for this transmitter.

List of some other transmitters I have worked on
Here is an index to some of my other transmitter projects including the Viking I.

(See also the Clegg, Conar, Gonset, Knight, Heathkit, Multi-Elmac, Swan, Polytronics, and Hallicrafters categories for more transmitters)

Sharp-eyed Tom caught an error in the description. I had previously identified the National dial as a Millen dial.
Date 5-3-13, correction 5-21-13


The full article "Sixty Years of Lafayette Radio" written for the December 2012 Monitoring Times was the previous project.



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