[Milsurplus] Re: [MRCA] Re: Angry Nine Woes

[Al Klase]

Yo Dennis,

I just wanted to thank you for this information.  The GRC-9 is now back 
among the living.  Even if I had deduced that C-114 was the problem on 
my own, it's highly unlikely that I would have torn the set down 
sufficiently to replace it.  Your shunt feed mod did the trick, and only 
took about an hour.

This is just another illustration of how important the Internet in 
general and these email communities in particular are to those of us who 
look after these relics.

Thanks again,
Al

W7QHO at aol.com wrote:
> 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
>
>
>   

-- 
Al Klase - N3FRQ
Flemington, NJ
http://www.skywaves.ar88.net/