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

[Al Klase]

Thanks Dennis,

A picture would be helpful.

VY 73,
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
>
>
>
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>   

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