[ARC5] Question on the 12A6 audio stage.

[J. Forster]

I havn't seen a print of what you are doing, but you may be able to get
more AC gain w/o disturbing the DC operating point of the tube by
bypassing the cathode resistor with a capacitor or a series RC network.

-John

============



> 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
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