[AMRadio] Mod xmfr

Brett gazdzinski Brett.gazdzinski at mci.com
Tue Oct 12 19:52:01 EDT 2004

One thing I don't like about doing different things with tubes is there is
real info on running 813's triode connected.
What's the distortion values?

I have a Gonset G76 that uses zero bias and drives the screen grid
of a pair of 6dq6 tubes as modulators.
I don't think its real clean.


-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Patrick Jankowiak
Sent: Tuesday, October 12, 2004 6:31 PM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] Mod xmfr

Ahh yes. The class-B 813 modulator. Glad to see it!

I'd like to comment about it from an audio standpoint as I have 
done this for audio with 807's.

I don't know how tough the 813 control grids are. I would suggest 
using some resistors to limit the current to the modulators' 
control grids to about 15 mA average (suggested based on the 
class C conditions in the tube manual; 20K worked for for 807's 
but the drive voltage was much less).

It is really the screen grids that must be driven to get the 
plate current up. The peak screen voltage may also be as much as 
750 volts (1500 g-g) for the 813 (the same value as the G2 DCV 
would be if it were operating AB1).

An old audio output transformer from a tube amplifier makes a 
good driver transformer because it will stand the voltage well.

The author might have some suggestions too.


From: "Jim Wilhite" <w5jo at brightok.net>
Subject: Re: [AMRadio] Mod xmfr

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