[Collins] 32S-1 Transmitter

[Dr. Gerald N. Johnson]

I haven't seen that double click. Makes me think the current in the 
relay coil is marginal and the +275 is dropping momentarily and so the 
relay is dropping out. Could be a sign the low voltage filter capacitors 
in the power supply have lost a significant amount of capacitance.

Then the two 68K resistors from +275 to the relay tube cathode have 
shown a propensity to drift high in value. They would be better replaced 
with a single 33K 5 watt wire wound or metal oxide film power resistor. 
Drifting high in value tends to make the vox relay tube hang the relay 
closed and not drop out, so I'd also be very suspicious of the other 
resistors in that cathode circuit having drifted high (as carbon 
composition resistors nearly always do) in value. The two 68K are R89 
and R112. The other cathode resistors are R87 and R88. R87 and R88 going 
high in value more than R89 and R112 would cause reduced plate current 
in the relay tube making the relay more sensitive to droop in the +275 
volt supply.

Has SB-2 been applied, converting the balance modulator from 2 to 4 
diodes for better balance? Something SB-4A depended on having been done.

Not necessarily related to this but has the selenium bias rectifier in 
the power supply been updated with a silicon diode? The selenium diode 
is way past its expected life time and since the -70 volts is used to 
key some of the transmitter stages if that bias voltage is low those 
stages may not be fully cut off. My suggested replacement is to find a 
three terminal solder terminal strip, middle terminal ground and 
mounting. remove the selenium and bolt the terminal strip in place of it 
and hook the wires that were on the selenium rectifier to the end 
terminals of the terminal strip and add a silicon diode like a 1N4004 or 
1N4007 (plenty overkill for voltage rating but easy to find for pennies 
each) with the proper polarity. Check the filter capacitors, the leakage 
of the old selenium rectifier is not good for them from applying some AC.

In the 32S transmitters the CW carrier is created by keying the tone 
(that is also sent to the receiver as a side tone) and running the 
balanced modulator and the VOX just like voice audio. PTT grounds R87 to 
lower the fixed cathode bias to the relay tube which makes me still 
suspicious of the relay tube circuits and the low voltage power supply.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 2/15/2017 4:54 PM, keckerle at chartermi.net wrote:
> I have acquired a 32S-1 transmitter. When keyed either by push to talk
> or vox for cw there is a double click of the vox relay. In the cw
> mode, a short burst of rf is emitted with the first cycle of the
> relay. On the second click, the transmitter will stayed keyed until
> reaction to the vox delay. I have examined the vox circuits and find
> that several service bulletins have been installed. One of which
> (bulletin no. 4a) is to solve this problem. However, the problem still
> exists. I have substituted tubes, adjusted bias, readjusted the
> balance modulator. Any thoughts? Karl K8FE
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