[R-390] my PTO problem, part II

[Roger Ruszkowski]

Felipe,
 
I think you just got a good sample of very good advice.
 
Tisha's  idea that you could be ahead to just buy another PTO
is in line.

I watched your two videos. (nice job).

You are moving the shaft and the guts have a back lash inside.

We all know this Is not good. PTO's do not have internal backlash.
That is part of what makes PTO so wonderful. OK a couple hertz back lash 
but not like your video.

As posted by the other Fellows do not let those cans scare you.

Do not disassemble the corrector stack.
Find some other method to make your self feel bad before you 
unbolt a corrector stack inside a PTO.

Ok with all the mental health warnings out of the way we can proceed.

Do some more video as you go. The next stage in R390 archiving.

We do not have photos of VFO guts in color or moving video.
We have not been in there since the camera was invented
We would all like to see what ever  video you can get up on the web.

And we thank you in advance for taking the time.
You are about to become famous if you take on this mission.
No money and little fame but we know who you are and will always thank you.

You will have to unsolder some heater wires as you go.
Not a big deal its just part of the disassemble process.

Inside, the shaft is just a nice acme thread on the shaft.
on the shaft is a carrier  with a matching set of threads in it.

Turning the shaft moves the carrier along the axis of the can.
The carrier slides a slug through a core not unlike watching a slug move
in one of the RF deck's tuning coils with cores.

The PTO slug is a bit larger than the RF deck slugs.

The corrector stack acts as the device that keeps the carrier from going round and round as the 
shaft is turned and thus forces the carrier to move along the threaded shaft.

I am thinking gummed up thread on the carrier mechanism. 
The runner on the carrier must follow the stack and not back lash.

Yours does. The carrier runs one side against the stack. The
back side is spring loaded against another rail.

As you change direction the shaft to carrier threads are so gummed up,
that instead of the spring having enough strength to hold the carrier against
the stack, the spring gets compressed, the carrier torques over to the other rail
(back lash) before it meets enough resistance that the threads begin to move.

The shaft bushing is also gummed up or when you dialed the PTO back and let go,
the spring would push the carrier back against the stack and you would get a counter lash effect.

I think you just need some cleaning inside the PTO to restore the VFO to good operation.

The stack we describe is like an S Curve. as it is not straight, over the tuning range.
It lets the threads get a little ahead or behind the curve to provide a more linear operation.

Once you get the PTO open you will see the coil has a magic non linear wind.
The coils got wound on the form by machine (lath).
A simple pattern lath. The pattern was hand make and tweaked to get it
as linier with the PTO slug as possible. Real black magic in the manufacturing process.

It was tired and retried to get it almost perfect.

Then the stack was adjusted by hand during assembly for awesome good behavior.

The secret to getting the stack together in manufacturing was the exact red color of the stick em.
Not true it was air dry time of the stick em.
The stuff was sticky enough to hold the mess in place but not so loose it would let things slide
out of adjustment. Not so stiff to make adjustment hard. Not to fast drying to prevent you from
getting the adjustment done.

Things were painted up and bolted loosely together.
Then the unit was let set on the line until it was about the right dry state.
Then you selected the unit when it had "cured" just right and popped it into the jig.
Hooked it up and with a gauge block S curve in one hand and a stick in the other hand
you sweep the corrector stack into perfect adjustment as you dialed the PTO through 11 turns or
so from stop to stop. And then tighten every thing up and run one more pass for a check.

It took longer to type this than it took to do it on the production line.

Not having the magic red stuff in hand with S curve guide, do not loosen the
corrector stack and thus cause it to come un adjusted.

Some brave souls  have been down this path.
You can read about them in the same history book you are about
to be recorded in if you do some video.
These wonderful  Fellows tell us that when they were done
the linearity of the PTO under maintenance was no better than 
when they started. The women at Collins aligned them as good as could be done.
And Fellows should not try and out do the women. 

Thus we tell you do not undo the corrector stack.

But have fun with the rest of it.

You can likely save in an afternoon.

And be happy that you did.
You will likely spend more time doing video for every one
than it takes to clean the PTO up.
Take the time and point out all the parts and what you find
/ found as you go.

Honest this is an effort that needs to be done.

Good luck with fixing the PTO and doing a video.

I hope there is enough info here to guide you through
the process,

I do not hang on my mail like I should.
but I will get back to you if you need more help.

If you have problems do some more post.
The Fellows will jump in and get you some timely responses.

If you are looking for some history or good words to put with the 
video just ask the Fellows here. You can see from the
mail there is plenty of experience to help you along.

Roger an old  33C4H