[ARC5] Question on the 12A6 audio stage.

[Kenneth G. Gordon]

On 5 Feb 2013 at 20:10, Geoff wrote:

> For reasonably matched headphones you have more than enough; if you want to 
> drive a 12" speaker then crank it up a bit but 3W is overkill in a small 
> room.
> 
> Carl

Yes. But I haven't made myself clear: I don't want or need any more power
output than 300 mW. That is plenty of output.

What I want is greater audio gain: I want to try to implement an
adjustable series-diode limiter, and inserting that after the detector and
before the amp will reduce the audio level noticably.

I want to try to compensate for that without adding an audio preamp.

There is another original design issue I am trying to figure out why ARC
did this: according to the tube manual, the DC resistance in the grid
circuit when using fixed bias should be no more than 100K: if using
cathode bias, no more than 500 K. Yet in the ARC designed circuit, that is
2 meg ohms. I suspect that they implemented some sort of filter, but I
haven't yet figured that one out.

Ken W7EKB