[ARC5] R-27/ARC-5 Hookup Question

[Kenneth G. Gordon]

On 20 Jul 2013 at 13:45, Neil wrote:

 
> I doubt it runs anywhere near 50 mA. It's connected as for Class A,
> but is starved for current by virtue of the high cathode resistor
> (1500 ohms if I remember correctly).

1500 ohms in early models: changed to 1000 ohms in later models to 
provide a bit more audio power output for some accessories.

> The 12A6 will deliver 3.4 Watt of
> audio if biased at about 35 mA, which implies a cathode resistor of
> 390 ohms.

Yes. Exactly that value according to the RCA Tube Manuals.

> With headsets and even in a noisy aircraft, the 12A6 is never called
> on to deliver more than a few dozen milliwatts.

It is specified at 300 mW with the 1500 ohm cathode resistor, and 400 mW 
with the 1K cathode resistor.

My restored ARC-5s will output almost exactly 400 mW....once I figured out 
how to accurately measure that.

Ken W7EKB