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

[Bob Weiss]

Thanks, Larry!  Only marking on the removed caps is a simple "10" on one
side, and one has a blue dot on it.  These are tiny little things, maybe
1/8" square.

Looking at the photos in one of the online guides, the unit shown uses a
different style of cap, which is clearly marked as 10 mmf, NP0.  So I
ordered an assortment of every value between 10 and 20 pF, in NP0/C0G
ceramic. I should have whatever value I need to get it back into the
adjustable range.

Now just to wait for the DigiKey order to arrive...

Bob W.



On Sun, Aug 26, 2018 at 8:05 PM Larry H <larry41gm at gmail.com> wrote:

> 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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