[R-390] Non Moment-of-Silence Mod

[David Wise]

I wrote up "Ending the Moment of Silence" and sent it to
Barry Hauser in January 2005. I never heard back.  Has anyone
heard from him recently?

I can't find the email I sent him, nor the writeup and scans.
I do still have the original drawings, if someone wants to
host them.

My mod does it with a two-pole switch, and two caps and
a resistor on a terminal strip behind the front panel.  I was
working with Mike Andrews to see if it would fit on an R-390
front panel.  I think the conclusion was no, which reduces the
cool factor a bit but it's still quite doable, just put the TS
somewhere else.

I abandon the old C551; one of the caps on the TS is 2uF and
replaces it.  The old one's just not wired right to use with
the mod.  The other cap is 0.15uF and does MEDIUM.  Where Collins
did it with a "straight" 2uF cap, I use 0.15 along with the
time-constant tube the same way LONG is done.  I empirically
determined the cap value.  The caps hang off the time-constant
tube's plate, and get switched to the AGC line or is bled to
ground through a 470K resistor that keeps the idle cap charged
to approximately the current time-constant plate while minimizing
its effect on the AGC action.  When a cap is switched in, the
maximum possible error is whatever the AGC line was at, which
is a small fraction of the total plate-to-AGC voltage.

I'm working from memory on the assembly section below; there might
be minor errors.  The cap connections to the TS worked for the
physical size caps I used; YMMV.

Written description of the wiring:
1. The wire that went to the old S107 SLOW contact (the time-constant
   tube's plate) goes to the two new caps.
2. The wire that went to the old S107 rotor (C551), disconnect and tape it over.
3. The other side of the new 2uF cap goes to rotor A on the new switch.
4. The other side of the new 0.15uF cap goes to rotor B on the new switch.
5. Switch SLOW A and MEDIUM B contacts go to the AGC line, which can
   be found at the MODE switch or the rear panel.
6. Switch MEDIUM A, FAST A, and SLOW B go to a 470K resistor to ground.
7. Switch FAST B goes to ground.  (Electrically, it could have gone
   through the resistor, but this way gives us a tie point.  Since
   the grounded cap is only 0.15uF, it doesn't hold the TC plate
   tight enough to interfere with the carrier meter, so we can
   get away with this.)

Written description of the assembly:
1. 5-terminal terminal strip, where terminal 3 is also the mounting lug.
2. Solder the mounting lug to a sheet-metal strip.  I'll figure out the
   dimensions I used and get back to you.
3. Jumper TS4 and TS5.
4. Solder pigtails onto terminals 1 and 2.
5. The 2uF cap goes between TS1 and TS4, on the lug side.
6. The 0.15uF cap goes between TS2 and TS4, on the back side.
7. Remove S107.  Tape off the old rotor wire.
8. Remove the nameplate.
9. Remove the upper right terminal board screw.  Don't lose the spacer!
10. Loosen the other TB screws.
11. Slip the sheet metal strip under the upper right hole, replace the
    screw through the strip, spacer, and TB, and tighten all screws.
12. On the new switch, jumper A1 and B2, and A2, A3, and B1.  Solder
    the resistor between B1 and B3.
13. Install the new switch and resistor.
14. The old SLOW wire goes to TS5.
15. The TS1 (2uF) pigtail goes to A.  The TS2 (0.15uF) pigtail goes to B.
16. The old MEDIUM (i.e. ground) wire go to B3.

I felt I did such a good blurb (plus I almost didn't find it),
I'm repeating it here:

From: "David Wise" <David_Wise at Phoenix.com>
To: <r-390 at mailman.qth.net>
Sent: Friday, January 21, 2005 12:19 AM
Subject: [R-390] Ending The Moment Of Silence


I did it!

I have perfected a mod that eliminates the carrier level
disturbance when switching the R-390/391/390A AGC rate.
Only the front panel wiring changes.  It is 100% compatible
with standard IF decks and those with the Lankford AGC mod.
This is how Collins should have done it, it would have cost
them next to nothing.  Like the carrier level pot, the
engineer just didn't think it through.

The mod I posted earlier had side effects that ultimately
caused me to reject it, although it was very compact and
easy to do.  This mod borrows an idea, but otherwise it's
totally new.  I have tested it extensively, and the
ergonomic improvement is just fantastic.  You'll never
realize how obnoxious and fatiguing the stock AGC switch
is until you try this.

Pros:
No more "Moment Of Silence" (SLOW to MED)
No more blasting (MED to SLOW)
Same time constants as before, or season to taste
Compatible with existing modules
Reversible (no holes)
No "box on the side", it's all internal
Works with decks that have a bad C551

Cons:
Needs a new AGC switch (2-pole vs 1-pole)
Needs a piece of sheet metal (if you want it to be neat)

Performance:
OLD
FAST-MED: Dip, Nothing, or Surge, depending on signal levels
MED-SLOW: Severe Overload for 1-2 seconds
SLOW-MED: No Signal for 1-2 seconds
MED-FAST: Nothing

NEW
FAST-MED: Nothing!
MED-SLOW: Nothing!
SLOW-MED: Nothing!
MED-FAST: Nothing

(Lest someone accuse me of advertising hype, I will qualify the above claims
to the extent that at very high signal levels (over 80dB), you may detect
a slight surge on MED-SLOW and SLOW-MED, but it's barely perceptible except
under artificial laboratory conditions, where it becomes merely 
"perceptible".)

Cost: About $15 and a couple of hours.


Regards,
Dave Wise


> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Tim Shoppa
> Sent: Wednesday, March 08, 2006 5:09 AM
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] Non Moment-of-Silence Mod
> 
> 
> >>> Perry Sandeen <sandeenpa at yahoo.com> 03/08/06 12:03 AM >>>
> > A while back a memeber posted that he had solved the "moment of
> Silence"
> > problem.  I and probably others, would appreciate if this would be
> posted to
> > the list. Regards, Perrier
> 
> I have not made the mod, but it was Dave Wise on this list in 
> Jan 2005,
> and
> he was unsatisfied with a mod made with the existing switch and he put
> in
> a two-pole switch and was satisfied. I never did see a 
> schematic, but he
> did drop some hints (seeming to not use the existing C551 and 
> presumably
> having a new one somewhere) and promise to write it up for HSN.
> 
> Others on the list have said it would be easy with a three-pole switch
> so
> I'm guessing some cleverness was needed for the two-pole switch.
> 
> Tim.