[ARC5] Added 6F6 audio stage.

[Kenneth G. Gordon]

On 19 Oct 2012 at 19:54, David Stinson wrote:

> I've never understood this issue of adding audio stages
> to Command Set receivers.

Neither have I: all those I have played with had more than adequate audio 
output. Of course, back then, I was using 600 ohm phones, so that may have 
been the difference. I ordinarily never used one with a speaker...except a BC 
band job I have here. But then I use that one with a 600 ohm to 8 ohm 
matching transformer. I can turn the audio gain up enough to really blast my 
ears.

> I've been playing these sets stock using matched speakers
> for decades.  They have all the audio I could want,

Well, I think part of the problem was perhaps those other users either weren't 
properly matching the output impedance, or they were trying to drive large, 
inefficient speakers.

However, in the AN/ARC-5 Maintenance Manual I have here, it DOES 
mention changing the 12A6 cathode resistor from 1500 ohms to 1000 ohms 
to gain more output. I think this was in the R-23A at least.

Remember, the early receivers had something like 8000 ohms output instead 
of anything much lower. Then a 600 ohm tap was added to the output 
transformer in later models.

Ken W7EKB