[R-390] PTO problem, part II

rbethman rbethman at comcast.net
Thu Jul 11 15:48:27 EDT 2013


I'd *much* rather tweak the Cosmos PTO linearity screws than to even 
think about a Collins corrector stack!

There really isn't that much to opening a PTO and cleaning out the dried 
out lube.

One can make a concerted effort to dry out the desiccant capsule. 
However, unless you KNOW the O-rings really seal, then there isn't much 
sense in doing so.  It is just like going through the drill of 
pressurizing the PTO with dry nitrogen.

There isn't much need for that either.  You would be assuming the 
Shrader valve core was still supple enough to seal.  You could replace 
that valve with a new one from a bicycle shop or automotive parts place.

IOW, your mileage may vary, and how far does one want to go?

I'm at the point that I am debating whether to even finish restoring the 
blue striper that I've been working on.

I just got an HRO-50T1 with the A, B, C, D, and AC coils with matching 
speaker.

I'm at the point of one radio in, one radio out.

Bob - N0DGN

On 7/11/2013 3:25 PM, Tisha Hayes wrote:
> Maybe it is the "DO NOT OPEN" warning on the can but the PTO is just a
> precision tuned variable inductor (Permeability Tuned Oscillator) there is
> a threaded rod that drives a slug into a coil and a few other compensating
> devices in there (caps and inductors). It definitely sounds like a
> mechanical binding issue if you are getting drag in one direction or
> springiness when tuning it. The electrical connections to the PTO are
> minimal, it is just an oscillator, you could rig it up on the bench and
> connect it to a good frequency counter to see it in action.
>
> Maybe the threaded rod is all gooed up with residue of 60 year old grease
> or someone else had been playing with it or the rod is bent or the carrier
> for the slug is canted out of alignment (from someone forcing it past its
> stops).
>
> Carefully cleaning it out. using a little bit of mild solvent to wash away
> the crud, cleaning up the o rings (on the case and the tuning shaft) and
> being very sparing in putting lube on the right spots is usually all it
> takes. Sometimes you need to remove a turn on one of the variable inductors
> if you cannot reach the end-point (there is an entire procedure out there
> that shows you how to do that with pictures and step by step instructions).
> As it has been said, that thing should tune very freely and if done right,
> the entire mechanical tuning assembly (racks, slides, gears, shafts, PTO)
> can be worked on so you can tune the radio with the tip of your finger on
> the knob.
>
> If you were enterprising you could take out the little desiccant capsule
> and bake it under low heat to dry it out completely (the color will change)
> and put that back in right when you are ready to button the thing back up.
>
> I would dread the idea of adjusting that swash-plate compensating disk.
> There is a special type of masochist who will tackle that. Fifty-million
> little screws to adjust linearity... euck!
>
> Tisha
>



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