[R-390] PTO Tenny Bolts and war strories

[Flowertime01 at wmconnect.com]

Seen a dozen examples of how to adjust the linearity ring, none tell the 
wrench size
for that tiny screw that I've been able to find. Most likely I missed that 
part of the instructions.

Best 73

Tom NU4G

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Tom, this is another one of the do it your self tool making adventures.
A small slot in the end of a shaft. 

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Personally, I think that inserting any metallic object into the innards of 
the PTO may possibly upset the reactance of the circuit.  73,Glen Galati, KA7BOJ

Glen, the PTO assembly has a transformer on it. The can has an adjustable 
slug like the one on the top of the Crystal Osc deck. Some of the models have a 
round "nut" on the shaft with two flats. You need a slotted tool to fit the 
flats, or you turn the shaft with a pair of pliers. A good home made slotted tool 
is better. So you are not really going into the PTO to do an adjustment. 

Strange but some times running the PTO for maximum signal will not give the 
best signal to noise. Mostly some where in the alignment process, you peaked 
the PTO transformer for maximum signal through the receiver. Usually some where 
above 8 MHz so the first mixer was not in the signal path mix. Do it this way 
until you have a week or so and want to play with your receiver. You can then 
try varying the coil adjustments and checking the signal to noise. Tweak and 
measure and tweak and measure and find the real good settings.

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I don't have any B+ on the output cables of any of the 390's I currently have 
on the bench.

Once upon a time in Nam I had an R390 on the bench. I though I had an adapter 
cube from an AN/URM 25 that had a cap inside it. It in fact had been rewired 
straight through as a barrel connector. I did not know this and it was the 
only reason I was not shot. Plugged that critter in between the receiver and the 
only frequency counter in the whole shop. Smoked the front end resistors out 
of the frequency counter. It was dead lined for almost 60 days until the parts 
come in. That shop had no counter and there were 200 plus 33's that knew just 
who it was that killed the important item of test equipment. We ran the PTO 
cabled up in circuit with a Tee and cap. We had no idea how the load changed and 
just did it that way. It was so much nicer to use the frequency counter and 
not count cycles on the oscilloscope display. Sorry I do not have an R390 
schematic to detail the exact reason the frequency counter will go up in smoke if 
not isolated. But I sure as hell barely lived through one experience with an 
R390 PTO that did smoke a frequency counter.

Roger. KC6TRU