[ARC5] Question on the 12A6 audio stage.

[Geoff]

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


----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Tuesday, February 05, 2013 2:26 PM
Subject: [ARC5] Question on the 12A6 audio stage.


> From the tube information, the 12A6 should be capable of 3.2 watts output 
> in
> Class A at 250 VDC plate and screen volts and about 30 mA plate current.
>
> Grid bias at this point should be about -12 VDC.
>
> Calculating what the cathode bias resistor should be under these 
> conditions
> gives a value for that of about 420 ohms or so.
>
> Yet the receivers normally have a 1500 ohm resistor as cathode bias for
> about 300 mW output. I read in a maintenance manual that ARC changed
> the cathode bias resistor to 1000 ohms to provide 400 mW output in some
> receivers.
>
> Measuring the grid bias on the 12A6 as it now is, I read about -14 VDC.
>
> In our use, considering only hacked receivers, could one change the
> cathode-bias resistor to 500 ohms 3 W and by that means achieve greater
> audio sensistivity?
>
> Kenneth G. Gordon W7EKB
>
> "Courage is being scared to death but saddling up anyway."--- John   Wayne
>
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