[Collins] KWS-1

Tue Apr 23 15:50:29 EDT 2013

Study the manual completely.

Check the PA filament voltage with a decent voltmeter. The filament 
voltmeter circuit uses two 1N34A germanium diodes, a 3900 ohm series 
resistor and the 1 milliamp meter. Reading high hints that the 3900 ohm 
resistor is at fault or that the meter movement has been changed to one 
more sensitive. As a crude check connect a 6 volt lamp, like a #44 or 
#47 pilot lamp to the PA filament circuit. Or that somehow the 120 volt 
filament transformer primary circuit is getting nearly twice rated 
voltage which will blow the transformer in a short time.

Tracing the circuits, I see that the plate will not turn on unless two 
interlock switches in the power supply are closed, at least one is on 
the front door, and one interlock switch in the PA compartment is 
closed, which means the cover is on the PA compartment, plus the 
emission switch has to be in CW, SSB, or AM and you have to wait for the 
time delay relay. The standby and cal positions do not allow the plate 
circuit relay to come on. Be sure that the lamp is good. Those 120 volt 
few watt lamps are fairly fragile. The time delay is to allow the 866 
mercury vapor rectifiers to heat up. If you don't wait, they will flash 
over and short the plate transformer and damage themselves in the 
process. If they have been moved, especially tilted, they need to have 
12 to 24 hours of filament power alone to vaporize any mercury from 
their anodes else they won't rectify and will short the transformer 
secondary. 3B28s are a bit more tolerant of voltage, but still like the 
time delay to get warmed up.

Then to really get plate voltage the power connector jumpers on TB503 
have to be correct for 120 vs 240 volts.

Once all the interlocks and lamp are correct, then there is a slight 
chance the plate relay can be bad, its coil is wound with fine wire that 
can easily have corroded open.

pp.collinsradio.org/archives/manuals/KWS-1%20The%20Care%20and%20Feeding%20and%20Other%20Trivia-Full.pdf 
is a good resource on the KWS-1.
pp.collinsradio.org/archives/manuals/KWS-1%20The%20Care%20and%20Feeding%20and%20Other%20Trivia-Small.pdf 
has all the essentials in a more compact file.

The PA tubes will generally benefit from 12 to 48 hours of heater power 
only to heat up the getter deposit and reduce the gas that has leaked 
through the metal to glass or ceramic seals, when they have sat for a 
long time.

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

On 4/22/2013 7:05 PM, THOMAS GRIECO wrote:
> This radio has been in my possession for years. Trying to get it on the
> air, but with difficulty
> Initial adjustments with filament switch on, PA Filament voltage is 11
> instead of six. Blower on. The Plate light will not turn on either.
> I am not technical at all so please bear with me. I have tested all
> tubes and fine. Fuses are ok. Input power at 115 vac.
> Suggestions? Pulled PA tubes out for now.
>
> K1SYN
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