[Collins] Need advice: diode load output on R-390A

[Dr. Gerald N. Johnson]

On Sat, 2009-10-03 at 10:05 -0700, C E wrote:
> All:Does this diode load output on the R-390A require a preamp? I would like to homebrew a 6V6 single ended amplifier to obtain better audio output.  Inquiring minds want to know. 73 de Cal, n6KYR/4
> 
> 
>       
Nearly all AM radios have two stages of audio (except for command sets)
after the detector to drive the speaker. The command set works better
with another stage. Usually a triode like a 6AT6 (half a 12AX7 would be
similar) to develop the 12 volts or so peak that the 6V6 needs. The
detector probably puts out no more than half a volt. And that's what is
at the diode load. The typical first audio triode has a mu of about 100.
I'm sure there are some octal based tubes with that high a mu, but I
don't remember them off the top of my head. But whatever was used as a
detector/first audio would be about right. I could look them up but you
will need to use what you have or can find.

Won't need a preamp for millivolts like a microphone or turntable
though.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer