[Milsurplus] GRR-5 Parts needed

[Richard Brunner]

WA5CAB at cs.com wrote:
  > Lacking that, AA1P wrote an article for ER some years ago on the 
AN/GRC-9 in
> which he shows a simple bi-polar transistor replacement for the vibrator in 
> the DY-105.  .......

It's in Electric radio, Number 108, April 1998, pages 30-35.  I did this 
to a GRR-5 a year ago for a friend, and it was very successful.

First, if you use a vibrator it better be the Oak vibrator.  The driving 
coil operates on 6 volts, or 12 or 24 volts through dropping resistors, 
and a substitute vibrator worked fine on 6 volts, but wouldn't work 
right with dropping resistors of any value.

The filament supply (vibrator) switching is done around 70 volts, so I 
used two high-voltage transistors, and the driving resistors were pretty 
high in value, maybe 150 k Ohms.  This is from memory as the notes went 
with the GRR-5.  Start high and reduce resistance until it works.  It 
happily oscillated/flip-flopped around 73 cycles, so don't worry about 
the 115 cycle thing.  Frequency is probably mostly set by the value of 
the buffer capacitors.

Do replace the selenium and copper oxide rectifiers with silicon - they 
are probably mostly non-conductive in both directions by now.

I "may" have disconnected C-118, the bypass at the transformer center 
tap.  I remember it either worked better with or without it.

GL
Richard Brunner, AA1P