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

[Carl]

Many of us use an old hi-fi or small audiotorum amp such as a 20W Bogen and 
similar fed from the diode output of a R-390 series. Sounds fine that way, 
especially with a good speaker.  I use a 3 way system from some old home 
entertainment unit with 12", 5", and a tiny tweeter all with the original 
crossover networks. It sure rocks the house with an old RCA hi-fi amp using 
PP 6V6's.

To feed a single 6V6 a single triode preamp is sufficient since you are 
running Class A and no driving power is required, just voltage. Half a 6SN7, 
6SC7, 6SL7, 12AU7, 12AX7, etc will be fine or their equivalents in a single 
triode such as a 6J5, 6C4, etc.

Carl
KM1H



----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: <collins at mailman.qth.net>
Sent: Saturday, October 03, 2009 9:22 PM
Subject: Re: [Collins] Need advice: diode load output on R-390A


> 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
>
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