[Milsurplus] Free - running osc at 7 MHz

[Kenneth G. Gordon]

On 22 Aug 2019 at 20:11, Hubert Miller wrote:

> I have a U.S. Army trans - receiver type BC-156. This is very similar
> to the "loop set" BC-148 which you may have seen. The BC-156 however
> tunes around 5 MHz and has instead of the large loop antenna, a
> transmitter coil inside, and worked into a wire antenna. The
> transmitter is one type 10, free running, and the receiver, 3x #30
> tubes, autodyne. 
> 
> Now, if the frequency is pruned up to 7 MHz, and using a stiff B+
> supply for the transmitter ( about 10 watts, I think ), will this be
> stable enough to use on the air ? 

Yes. 

These types of transmitters are being used regularly on the air, especially during the 
Antique Wireless Association's Bruce Kelley Event which takes place yearly, usually around 
January.

Might you have a schematic of this transmitter I could see? What type of oscillator is it? 
Hartley, Colpitts, TNT, TPTG, what?

I have a push-pull pair of 211s in a TNT configuration I will use on the air this winter.

>From experience with these 1920s designs, I can give you a better idea of what to expect 
from it on 40 meters once I know what type of oscillator it is.

FYI, KM1H used a push-pull self-excited oscillator somewhat like yours to earn DXCC 
recently. No one he contacted even knew what his transmitter was from the sound of it on 
the air.

Your "stiff B+ supply" is primarily the key to getting it to sound good.

Ken W7EKB