[R-390] Cosmos question

[Tim Shoppa]

"Jon" <jonklinkhamer at comcast.net> wrote:
> Have a question concerning my Cosmos PTO. I have it on a test jig and I'm
> experiencing what I will call hystersis. I can zero the frequency at 3.455
> exactly on my zero reference point on my test dial (great). Now I can be off
> 1000s of hertz depending on going CCW or CW and then going back to my zero
> point reference which I stated at 3.455. I can always get back to my 3.455
> by noting the new frequency and rotating CCW or CW to get back. I hope I'm
> making sense. Has anyone experience this.

Test Jig = "in the 390A chassis"?

The mechanical phenomenon that causes hysterisis is "backlash". This is
due to looseness in couplings, gearings, assemblies, etc.

If it's in the 390A chassis, the first place to look is the Oldham coupler
and the anti-backlash springs.

If it's off the 390A chassis, then I would suspect mechanical looseness
in the PTO chassis itself, requiring a complete teardown/clean/
reassembly.

There are gears in the front of a Cosmos driving the corrector stack
but the most relevant gear for fine-tuning is the worm gear that
drives the core in and out of the main inductor.

Have you listened (as opposed to just watching numbers on a fequency
counter) to the PTO? Is it smooth except for backlash, or does it
sound "squirrely"? In the case of my gunked-up PTO, it was within
a few hundred Hz of the dial but it never *sounded* right when
reversing direction, making lots of wiggly squirrely noises when
beating a carrier or CW signal. I completely tore my PTO apart earlier
this year, cleaned out a bunch of gunk, realigned and put it back together
and am very happy. Was documented on this list.

Tim.