[Drake] Drake 2B AVC

[Dave Edwards]

Perhaps though, when the -1.35 to -1.5 volt requirement for the sensitivity 
pot was determined, there was nothing better than the 11Meg input VTVM. That 
may be the reference. Perhaps you should use a VTVM??
....Dave
----- Original Message ----- 
From: <windy10605 at juno.com>
To: <drake at mailman.qth.net>
Sent: Sunday, July 24, 2005 9:51 PM
Subject: [Drake] Drake 2B AVC


> Thanks to all who have responded to the above. This is where I'm at:
>
> As Garey and Byron mentioned, the AVC circuit on this receiver is VERY
> high impedance and any efforts to measure voltages at the AVC terminal
> must be done with a high Z meter. Just as an indication, the
> "sensitivity" pot on the back must be set to -1.35V to -1.5V with the RF
> gain
> all the way up. When I use a calibrated Fluke which has a 1000Meg input
> impedance on the 2V scale and set -1.35V another calibrated instrument
> with a 10Meg input measures -1.22V (which is not too bad ....but my
> little calibrated DVM which I was using, measures only -0.64V. That means
> it has a very low input impedance ....lower than I thought, anyway. This
> level sets the upper level of the AVC bias for the RF Gain control, and
> it goes all the way to -9V at the other end.
>
> Going to a 6EA8 from the 6U8 improved the signal level about one S-unit.
> Changing to a new 6BA6 IF tube (also used for the S-meter) causes it to
> kick somewhat higher (2-3 S-units) indicating a higher Gm which the new
> tube does have.
>
> The other modification I'm considering is the 6BN7 to 12AX7 audio change
> to allow more volume and replace the two diodes with solid state
> 1N914 diodes.
>
> 73 Kees K5BCQ
>
>
> ______________________________________________________________
> Drake mailing list
> Home: http://mailman.qth.net/mailman/listinfo/drake
> Help: http://mailman.qth.net/mmfaq.html
> Post: mailto:Drake at mailman.qth.net