[Milsurplus] Re: Angry Nine Woes

[W7QHO at aol.com]

In a message dated 8/1/07 4:09:38 PM, al at ar88.net writes:


> I'm back to working on an AN/GRC-9 that's been lying around here for too
> long.  No TX output as there is not enough grid drive to the 2E22 to
> actuate the safety relay that turns on the screen grid.  DC on the PA
> grid (pin 5 of the test connector) is about minus 12-15 volts.  It's
> supposed to be -60.  All tubes have been checked.  Voltage and
> resistance on the tube pins checks OK.  Grid drive to the driver tube is
> maybe 10% low.  Tuned circuits seem to peak.  Same problem on all three
> bands crystal or MO.  (This is giving me /deja vu/.  I had the same sort
> of trouble with a 2-meter Gonset that I gave up on.  I'm a receiver
> guy.)  Any suggestions?
> 
> 
Al, et-al,

GRC-9 drive problems; ah, yes...   Following information sent around last 
fall.

"Speaking of GRC-9s, there is a capacitor in these sets that requires a major 
disassembly effort to replace.   C-114 bypasses the cold ends of the PA 
driver tuned circuits and is buried inside the can (T-104) that houses these coils. 
  Leakage is manifested in low grid bias and hence improper biasing of the 
2E22 suppressor grid when operating in the Phone mode.   This problem has 
surfaced in four different rigs out here in the past year.

See ER #118 for a description of just how hard it is to replace this 
component.   In response to this I've come up with a considerably less painful 
solution as outlined below.   Implemented in three different sets so far with 
excellent results.   The mod essentially involves grounding out the failed component 
and shunt feeding the 2E22 grid.

By removing the variable cap assembly it is possible to reach the point where 
the lead coming out of the can from Point 3 on the circuit diagram connects 
to the wiper on "S101H Sect 4 FR".  There are two blue wires coming off this 
point too, one running over to pin 5 on the metering socket and the other to 
R106.  Cut the two blue wires loose and then GROUND the lead coming out of the 
can from Point 3 where it connects to switch wiper, see above.  In cutting the 
blue wires snip off so as to give yourself as much lead length coming out of 
the cable they run into as possible, see below.

Next, remove the short wire running from pin 3 (grid) on the 2E22 socket over 
to the adjacent switch section and replace this connection with a .001 mica.  
Connect the two blue wires (see above) through a small RF choke to pin 3 on 
the 2E22.  Bypass the cold end of the choke (where the blue wires are 
connected) through a .01 cap to ground.  Rather than leaving this end of the choke 
dangling I anchored the wire lead through a small hole drilled through one side of 
the fiber core of adjacent L101. (Picture available on request.)

Tight quarters here, lots of hemostat work and a bit of cussing too, but MUCH 
easier than getting inside T104.  No room for a full size 2.5 mh RF grid 
choke but found a miniature version that worked FB.  Inductance here probably not 
too critical.  Check carefully to make sure nothing shorts when the back 
section is folded up in place.  I had to shorten up one of the screws that holds 
the interconnecting cable socket in place to prevent interference."

hope this works for you.

Dennis D. W7QHO
Glendale, CA



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