[Milsurplus] Re: AN/GRC106A for sale

Mon Jun 28 23:37:21 EDT 2004

I have a few words on the GRC-106/A set in general.

Buy it. and..

The exciter can be judged to a great extent without the meter. 
Although it has no noise blanker, it is as sensitive as any 
fairly modern (non DSP) ham radio, and much more resistant to 
overload of the front end as it has 29 bands (MHz bandswitching) 
  It is resistant to EMP due to tube front end. It is a triple 
conversion synthesized (translation method) unit with all 
transistors (no IC's) except for the front end tubes (and those 
same tubes are also the drivers for the AM-3349 amplifer). It may 
be either germanium+silicon or all silicon (more desirable).

Judging the amplifier is another matter. Without the meters for 
tuning the PA  output, etc, it is hard to judge if or how well 
the amplifier works, and easily possible to damage the 4CX350F 
output tubes due to improper tuning (not so much by plate 
dissipation, but the screen grids will go up and cause a direct 
or dynamic short, as there seems to be no real effective screen 
protection). It is always safe to remove the PA tubes, and try 
the amp without meters, to see if it goes through all the steps 
and keys up. It is a complex unit with many interlocks and 
synchronized electromechanicals. Collins would be jealous. Any 
problems which are not immediately evident only seem confounding 
or mysterious until you find the cause. Do not dismay, it is no 
more complex than a mixed signal electromechanical computer. The 
amp may come on, and appear to autotune, but not key, due to some 
obscure failure (and this is where the fun begins!) I have posted 
a few of these oddities in the armyradios yahoo group, and 
there's alot of info there from others too. So it is apparent I 
really like this big green radio.

The full manual which is about 4" thick (or a CD, but are rare 
and not as good as the book as a couple schematics are corrupted 
[FO-27 and FO-28] -your tax dollars at work) does have step by 
step troubleshooting procedures, and is highly reccommended, or 
perhaps even mandatory.

Be sure you get all 3 of the -34 manuals if you intend to work on 
the unit yourself as they have the real details so that you can 
acually fix modules instead of replacing them. I own three of 
these radios, and have repaired several more of them, and I like 
them very much. There's a big test set for the modules, but 
whether it's worth it or not.. I have fixed a few modules, most 
are not too bad, but you will have to make up an extension cable 
to get the module up out of the set to get at the innards. Watch 
out for bent contacts on the turret in the amp, as well as burned 
contact blocks in the amp. The -34 manuals by the way are not 
available from LOGSA as they are still deemed 'restricted'. 
Plenty of manuals have slipped out through DRMO etc, so it should 
be able to be found.

GRC-106 Manuals
TM11 5820-520-10 (operators)
TM11 5820-520-12-HR
TM11 5820-520-20 (module level repair)
TM11 5820-520-20-P1
TM11 5820-520-20-P2
TM11 5820-520-34 (theory and component level repair)
TM11 5820-520-34-P1 GRC106 parts and tools list
TM11 5820-520-34-P2 GRC106A parts and tools list

I can vouch that it is a very rugged and trouble free set as long 
as it is tuned properly. It needs to warm up the oven for about 
10 minutes minimum, and they are often left on standby to keep 
the oven on and the few tubes warm (oven only mode available as 
well). It is 400W PEP CW, USB, or Carrier+USB (AM mode). LSB can 
be received by using the BFO and the CW position. It has an FSK 
position, but it is AFSK actually requiring an audio input.

Please check PS Magazine back issues as well for revised 
operating cautions (Soldiers were not tuning properly, and not 
allowing time to stabilize the frequency standard, blowing the PA 
tubes up due to being off frequency). You can also unofficially 
use 4X150G tubes if you are very careful not to overload them and 
only use SSB (CW and AM overheats them).