[ARC5] Volume control - ARA receiver

[Kenneth G. Gordon]

On 12 Jul 2016 at 2:25, J Mcvey via ARC5 wrote:

> It's fine with just the RF control. No input = no output.

Correct.

> They don't have real
> powerful audio,

Well, depending on the model (early vs late) the AF output is either .5 watts 
or .75 watts. I have found that if the impedances are properly matched and a 
speaker is connected, even 0.5 watt output is enough to rattle the windows

> so they just ran it wide open and vary the the RF gain which
> determines how much audio will appear at the detector.  This was a old time
> legacy design that was shared by many radios in the pre-war era.

Actually, as I understand it, there is an AF gain control in the external controls 
or rack somewhere. Mike would know. (Either one). Maybe that was on the 
intercom though.

In any case, I have found that incorporating an AF gain control in those 
previously modified receivers is very useful.

What I do is to replace the 2 megohm grid resistor of the 12A6 with a 2 
megohm audio-taper pot, with the normal feed to the grid connected to the 
wiper of the pot instead.

Ken W7EKB