[R-1051] Frequency Standard Modules

[Dennis McLaughlin]

Geoff Fors wrote:
> Just curious if anyone can comment on the differences and interchangeability
> of the frequency standard modules in the R-1051 B through H-suffix models.
> 
> I have modules which I think are from G or H models, because they have a
> window on
> top marked "index"  as well as the 3 position switch and the coarse-fine
> holes, and carry FSN's of :
> 
> 6625-01-055-5294 and
> 6625-01-168-9757
> 
> I haven't had a chance to pull the standard module out of my "B" model to
> check the differences and was wondering whether anyone has used these style
> modules in a B model.
> 
> Geoff Fors
> WB6NVH
> 
> _______________________________________________
> R-1051 mailing list
> R-1051 at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/r-1051
> 
Geoff,

I have a plain jane R-1051.  I have installed the newer style used in 
the H model and other equipment that I bought on ebay.  6625-01-055-5294 
Assy 01A228203-01 is installed now.  Works great.  A 6625-01-163-1323 
also works.  The frequency multiplier board is almost the same as the 
older 6625-00-078-4718 style.  A few transistor type changes. Has a 
light bulb not an LED.  The oven is totally different.  The power 
transistor that regulated the power to the oven heater is mounted on a 
heat sink, not the oven.  This lowers the junction temperature of the 
transistor.  The other changes are a voltage regulator to limit the 
voltage to the oven and oscillator preregulator to 30 volts and a 15 
volt preregulator for the oscillator board.  The output frequency seams 
to be more stable.

If you have an RF voltmeter measure the 10MHz output at the module with 
the cover removed and adjust C33 for max. with the six pack installed. 
10MHz output should be between 20 and 40mV.  The adjustment is touchy.

  The model shown in the 1051H manual uses a power resistor and a zener 
diode for the 30 volt regulator.  The 6625-01-055-5294 adds a power 
transistor to the regulator and a smaller power zener diode. The changes 
in design seam to be due to the resistor in the 10 volt regulator on the 
oscillator board running to hot.  The regulator is a resistor and a 
zener diode.  The older styles put 28 to 32 volts into the regulator on 
the oscillator board.  The newer ones preregulate down to 15 volts from 
the 30 volt regulator. The 15 volt regulator IC runs hot. A 78M15HMQB. 
There is also some TTL logic to automaticlly switch from external 
frequency standard to the internal one when the signal drops below a 
threshold value.  This requires a 5 volt regulator which also runs hot.

The oven uses the same PTC resistor to sense the oven temperature.  This 
  resistor, the power transistor mounted in the bottom of the oven on 
the old style and the variable resistor on the oscillator to adjust the 
oven temperature are common parts to fail.  One of there fails and cooks 
the oscillator board.

Dennis McLaughlin