RE: [HCDX] Collins R390A Dilemma
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RE: [HCDX] Collins R390A Dilemma



How linear is the PTO (permeability tuned oscillator, it is ganged to the

tuning knob, along with the gear train for the IF)? In other words, on a

given band, is it off by the same amount at the top, middle, and bottom of

the range? Is the error constant in a given band, just different depending

on the band?

 

If so, you are in good shape. The radio is essentially a tuned IF with fixed

crystal-controlled converters in the front end. As long as the PTO is

linear, a good alignment should fix her right up. If the PTO is off, it can

be fixed, providing that it is still in the adjustment range. Special tools

to adjust and lock the trimmers in the PTO are required, and it is a bit

tedious to do, but not especially hard. Just time consuming, making small

changes and checking the linearity across the dial. I did one 75A4, and I

remember it took all day doing the adjust/check/readjust/recheck thing. But

it came out OK in the end. If the PTO is out of adjustment range, it will

have to go to the factory, if they still do that sort of thing, or replace

it with another PTO.

 

I am going to guess that she just needs an alignment, since I think you are

saying that she is off differing amounts on each band. The lowest band uses

just the IF, so that is a good indication as to the linearity of the PTO

itself.

 

I can't remember the links at the moment, but there are a lot of good web

pages detailing the steps to align the radio and the PTO.

 

Does yours have the meters still installed (signal strength and line-level)?

 

Rick