[Milsurplus] GRC-9 Drive Problem

[Richard Brunner]

Re:
"> I have been chasing a drive problem on my AN/GRC-9 transmitter, the drive
> falls off with increasing frequency and is especially bad on 40 metres and 
> above. The drive levels even down on 2 Mc aren't very good with an RF 
> output of about 5 Watts on CW. ..."

It could merely be a driver misalignment problem.  Near the top of tuning 
ranges, adjust C-111, C-112, C-113 for maximum drive, and near the bottom of 
the tuning ranges adjust inductors T-104A, B, and C for maximum drive. 
Also hope and pray the problem is not C-114, the grid driver bypass 
capacitor, which is in the driver coil box, and is the most inaccessable 
part in the set.

To get at the capacitor, to use the vernacular, "It ain't easy."  See my 
article, "GRC-9 Operating
Notes," in Electric Radio, Nr. 108, April 1998.  Briefly, to remove T104:
1.  Remove all tubes and put them in a safe place.
2.  Remove the VFO tuning knob and condenser.
3.  Unsolder the small RFC from the tank coil.
4.  Unscrew the standoff insulator from the corner of the T104 can.
5.  Unbolt the 2E22 shield.
6.  Push the above components aside to provide "Wiggle Space."
7.  Remove 4 nuts attaching T104 to the chassis.
8.  Remove screw on the side of can T104.
9.  Run the tuning slugs all the way down. This is necessary due to an
interference between the slugs and the top mounting screws if the slugs
are up when you try to remove the coils in step 11.
10.  Pull the can up a bit to allow wiggle space, and remove (6) coil
mounting nuts
11.  Push the coil mounting screws inside the can, and gently wiggle it out
12.  Replace C114 while you're in there.
Reassembly:
13.  Make sure the coil mounting screws are tight and will not rotate.
14.  For re-assembly, make three thin 3/8" ID paper tubes to guide the slugs
back into the coils.  They may be removed later from the bottom, and if left
in place will do no harm.
15. Put the can onto the coils with the guidance tubes, wiggle into place on
the chassis and attach with (4) nuts.
16.  Wiggle the coils to get the mounting bolts through the mounting holes.
Put nuts on the top bolts only, as the bottom bolts are too inaccessible.
Scrunch a length of solder onto a nut to hold it, and thread onto the bolt
with a small screwdriver.  Tighten with a wrench.
17.  Line-up the bracket supporting C114 inside T104, and attach with a
screw in the side of the can.  A length of wire with a small hook on the
end, used to line it up and to prevent turning, is a big help.
18.  Retrace steps 1 through 5.
19.  Re-tune the transmitter driver stage.

Having done this once, it doesn't look so formidable now.

Output should be 10-15 Watts, maybe 20 Watts with high B+.

Also see "Electric Radio in Uniform, the AN/GRC-9," by Walt Hutchens, KJ4KV,
Electric Radio, Nr. 6, October 1989, pages 4-10.

GL
Richard Brunner, AA1P