[AMRadio] Minature Mobile Transmitter

Mike Dorworth,K4XM k4xm at arczip.com
Tue Oct 4 20:56:42 EDT 2005

For class A audio,with a pentode, you do not need a step down transformer
of 2.66 or 5 to 1 to each half of the secondary. You don't need push- pull,
and it is OK to use cathode bias which can never be used for class B. Zero
Bias Class B triode operation is to save current while idle and take a big
peak for a little while. Class A is a power waster, that is why the majority
of later car radios used a single Class A Transistor. The cars had bigger
batteries and alternators. Ditto the 6V6, 6AQ5, 6K6 output stages. Notice
that all the old communications  receiver that used the single ended Class A
stage called for 10 percent distortion, Ugh!

----- Original Message ----- 
From: <bcarling at cfl.rr.com>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Tuesday, October 04, 2005 5:21 AM
Subject: Re: [AMRadio] Minature Mobile Transmitter

> On 3 Oct 2005 at 0:39, Bob Bruhns wrote:
> > That's amazing.  Can't argue with success.  And
> > the 7.5W-300V-16K p-p adds up.  The published
> > 12AX7 plate dissipation spec must be overly
> > conservative, and the cathode must be pretty
> > efficient.
> >
> > I always thought of the12AX7 as an audio preamp
> > tube.
> It is... There HAS to be a good reason why manufacturers
> used things like 6AQ5 and 6BM8 for 4 watt audio output
> stages instead of a 6C4 or 12AX7 !!
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