[R-390] AGC Slow - Moment of silence

[Larry H]

Hi Dave,  This new one looks great.  I sketched it out on a schematic and don't see a thing wrong with it (of course).  This is much easier to do.  This one does not require dropping the front panel, where as the last one would to get at S102-5.  I like it.
Regards, Larry
      From: David Wise <David_Wise at Phoenix.com>
 To: R-390 Forum <r-390 at mailman.qth.net> 
 Sent: Friday, May 13, 2016 5:23 PM
 Subject: Re: [R-390] AGC Slow - Moment of silence
   
Aw heck, typo, corrected below.

-----Original Message-----
From: David Wise 
Sent: Friday, May 13, 2016 4:28 PM
To: R-390 Forum
Subject: RE: [R-390] AGC Slow - Moment of silence

I realized that AETMOS-51 can use C551 or an external 2uF cap.

THE MOD
Take 3
C590 on the grid side, C591 in series

If C551 is okay, omit steps 1 and 2.

1. Disconnect and tape off the wire (C551) at S107-7 (wiper)
2. Connect C590, 2uF, between S102-5 (MGC contact; V506A grid) and S107-7
3. Disconnect and tape off the wire (ground) at S107-9
4. Connect C591, 0.15uF, between S107-8 and S107-9
5. Connect R590, 10M, between S107-7 and S107-8

PRINCIPLES OF OPERATION

SLOW: Unchanged (V506A with 2uF of Miller feedback).

MED: V506A with 0.14uF of Miller feedback).

Instead of using C551 passively, we operate like SLOW, only with a smaller cap.
C591 (0.15uF) in series with C551 gives about 0.14uF of feedback capacitance,
which V506A multiplies to about 1.9uF of effective capacitance.
R590 (10M) keeps the high end of C551 near V506A's plate voltage, and keeps C591 discharged.

FAST: Unchanged.  R590 (10M) keeps the high end of C551 near V506A's plate voltage.


Regards,
Dave Wise

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