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

[Bob Weiss]

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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