Tubes with 12 or 28 v Plates?

Hue Miller kargokult at PROAXIS.COM
Thu Jan 6 02:16:08 EST 2000

At 08:32 PM 1/5/00 -0500, Paul Litwinovich wrote:
>> Can anyone tell me what tubes are useful in a TX
>> application that are also efficient with 12 or 28vdc
>> plates?
>> - Thanks! & 73, DavidC  K1YP

>12BE6, 12BA6, AND 12AT6  Were the common tube compliment of the 1960s hybrid
>car radios.

--Mmm, not quite right. The sets actually known as "hybrid" used the "space
charge" tubes such as 12AD6, 12AF6, 12AE6....there were quite a few others in
this family of tubes designed to run off 12dc on the plate. Quite a few boat
radios used the same kinda tubes.
The aforementioned specific tubes for converter, IF, and lowlevel audio
just won't develop enuff plate current to make an oscillator for more than
demonstration purposes, or maybe QRPP. One type i note, 12K5, is listed as
40mA at 12 volts plate class A, so there's hope for a transmitter with this
I think that with 28 volts you can use the 25L6 and maybe later TV tubes
with that filament to develop a healthy part of a watt. Some farm radios of
the 1930s used "normal" high plate joltage tubes run at 32volts from the
farm windcharger supply to make practical loudspeaker home radios.
Another possibility is the 28D7, a twin triode developed for communications
equipment. It was used in the BC-1206 as headphone audio output and in the
MBF navy transceiver as output (altho in this case with plate B+ higher
than 28 volt).
So you actually have quite a few choices. I think i would go with the 25L6
idea for easiness of locating tubes. Actually, 12v is more practical tho.
And if you drive the supressor grid from a carbon mic and transformer, you
can have a complete AM/CW transmitter with maybe a couple hundred milliwatts
power. ( power level WAG on my part.)
Hue Miller

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