[R-390] EAC Rocketship project--PTO capacitor types?

[Larry H]

Good work, Bob.  A ceramic or silver mica should be fine.  The ntc value
should be about 50% to 100% more than the originals.  It should be readable
on them, and they are usually 100 to 400.

Regards, Larry

On Sun, Aug 26, 2018 at 3:43 PM Bob Weiss <bobweiss1967 at gmail.com> wrote:

> Taking a dive into the Cosmos, I guess....
>
> Have a used unit on the way, in unknown condition.
>
> Spent a few hours diving into my unit, with the help of those
> excellent photos.  The solution on mine seems to be reducing the
> capacitance across the main tuning coil.  I temporarily replaced the 2
> 10 pF ceramics across the main cap with a single 14 pF silver mica and
> it seems to get it much closer, probably into range of the adjustment.
>
> What type and temperature coefficient should the permanent replacement
> cap(s) be?  The originals were a pair of tiny square ceramics, which
> the Y2K manual parts list just refers to as a non-replaceable part of
> the PTO can assembly.
>
> Any thoughts on replacing the dessicant capsules in the can?  I
> removed the ones that were installed after reading about them
> splitting open and making a mess.  Have to look through McMaster carr,
> and see if they have anything similar.  Needless to say, the nitrogen
> charge was long gone, and the rubber o-ring seals are all rock hard.
>
> 73,
> Bob W.
>
>
>
> On 8/24/18, Larry H <larry41gm at gmail.com> wrote:
> > Glad you're making progress, Bob.
> >
> > If the pto is good mechanically (tuning shaft: 1. turns smoothly, 2. no
> end
> > play, 3. has good light turning resistance (not too hard), and 4. is
> > straight,  then it might be worth while to try to save it.  Also check
> that
> > there is very little slack in the linearity compensator gear when the
> main
> > shaft is turned back and forth.  You can look through the linearity hole
> > and watch the disc move.  There's lot's of good info about them.  There's
> > '*A
> > JOURNEY THROUGH THE COSMOS (PTO) by *Jim Miller at:
> > http://www.r-390.com/cosmos.htm  and mine at:
> > http://www.r-390a.net/Pearls/PTO_Cosmos_Observations.pdf and Tom
> Marcotte's
> > in the PTO section in the Pearls at the end:
> > http://www.r-390a.net/Pearls/PTO.pdf
> >
> > 18 kh is too much to correct by removing 1 turn off of the ep coil.  One
> > turn on a cosmos is about 6 kh.  This is less than the others, due to the
> > extra compensating coil in the circuit.
> >
> > Keep at it and have fun.
> >
> > Regards, Larry
> >
> >
> >
> > On Fri, Aug 24, 2018 at 5:51 PM Bob Weiss <bobweiss1967 at gmail.com>
> wrote:
> >
> >> Have been plugging away on the EAC, and have it up and running , at
> least
> >> well enough to pick up local AM stations.
> >>
> >> The Cosmos branded PTO cannot be endpoint adjusted, as the adjustment
> >> screw
> >> runs out of range. Unit is out by 18KHz over the 10 turns travel.
> >>
> >> It appears that a previous owner was already poking around (first sign
> of
> >> any work other than tube changes) in the PTO the factory seal tag has
> >> been
> >> violated, and signs of the green mounting screws and the endpoint adjust
> >> screw having been "diddled"with quite a bit previously.
> >>
> >> Anyone have a good PTO available, or thoughts on how to repair this one?
> >> I
> >> have heard about removing a turn from some internal coil?
> >>
> >>
> >> In other project notes, I was surprised to find the meters on this unit
> >> to
> >> be just as "hot" as the old ones I pulled from my Stewart Warner.
> Trying
> >> to track down a suitable set of replacement meters for this one. I had
> >> heard that the later production were supposedly non-radioactive, but
> this
> >> being one of the last units built, I wonder how it got hot ones, which
> >> look
> >> original, no evidence of swapping.
> >>
> >> The cores in the IF cans are VERY stiff/sticky, particularly the bottom
> >> slugs.  Any particular solvent/heat technique to break them free without
> >> damage?
> >>
> >> Found a couple completely unsoldered connections in the AF deck, on the
> >> filter can sockets. They do seem to have been making good contact, no
> >> sign
> >> of arcing. Assembled on a Monday, and inspected on a Friday, I guess?
> >>
> >> After the recent thread about the filament choke burning up in the RF
> >> deck,
> >> I checked the area on mine. Mine was also quite close to grounding out
> on
> >> the chassis, but no sign of arcing/burning, so I redressed it slightly
> >> and
> >> it should be fine.
> >>
> >> Have lined up a set of IERC shields to replace the cheap silver ones
> >> (many
> >> of which are cracked/split). Guess the civilian market didn't rate
> those?
> >> Or were they all field change additions?
> >>
> >> The civilian unit apparently didn't ship with the tools attached to the
> >> rear panel. The spring holders for them were never installed.
> >>
> >> 73,
> >> Bob Weiss N2IXK
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