[R-390] COSMOS PTO, starting over again.

[Phil Atchley]

Hi.
Y'all are gonna to get tired of all these Cosmos PTO's.  But!  Let me =
tell
you, you're not as tired of them as I am of working on the blasted =
thing.

In trying to adjust the linearity of it after having changed out the bad
6BA6 tube I noticed that I wasn't getting "repeatability" on the =
linearity
screws.  I could tweak one, tune away and come back and it'd be off.  In =
the
most severe cases by a couple KHz, most of the time a couple hundred or =
so.
What was maddening is that it demonstrated no discernable pattern as to =
when
or where. . .        =20

So, I've stripped the PTO down completely AGAIN.  All the way down to =
the
inner sanctum where the linearity "guts" lie.  Upon pulling the "spring =
ring
thingy" and checking the plunger of the linearity coil I noticed just =
the
tiniest bit of roughness or grittiness in its action.  Very minute, but
possibly enough to prevent repeatability of the core position.=20

So, I unsoldered the wires of the coil and removed it thinking that =
would
allow me to remove the Plunger and clean/lube it.  WRONG!!  It is a =
sealed
assembly with the coil.

So I did the next best thing.  I used some semi-synthetic grease and =
applied
it to the part of the plunger that was visible (after wiping that part
clean).  I did this a couple times, each time working the plunger in as =
far
as it'd go to spread it around.  NOTE: DON'T use oil as it may run down =
the
plunger and contaminate the coil core.  The plunger now is smooth and =
silky.
Don't know how many years it'll last before the grease hardens some but =
I've
had good luck with this Valvoline DuraBlend  on many items.  It "seems" =
to
stay "greasy" and not harden any.

Next, I am backing all the linearity screws out again and pre-setting =
them
one turn clockwise to give me a good starting point and the BIG job of
tuning will start again.  Luckily I have that down rather pat.  As I
mentioned before, I tune it IN the receiver.  I leave the rear mount
attached to the PTO (but not screwed to the receiver frame), leave the =
front
screws unscrewed and that allows me to hold it in place against the =
Oldham
couple for tuning and EASILY lift it out for tweaking. =20

NOTE to Barry:  This doesn't put any undue shock on the PTO as I lift it =
out
very easily and tilt it back for adjustment.  I HAVE to be gentle so as =
to
not knock the tuning shaft position out of place.

HEATER NOTE:  This time upon disassembly I completely removed the =
thermostat
and the heaters from inside the PTO.  I NEVER use them anyway and they =
just
complicate the teardown-rebuild of the unit.  Yes, I'll keep the =
insulation
intact as I'm sure it adds to the thermal stability. =20

One FINAL note.  IF this doesn't get it this time I'll be giving up on =
this
PTO and will be looking for a Collins or other unit ;-)

73 de Phil, KO6BB

****************************************************
*  DXing THE WORLD WITH THE FOLLOWING EQUIPMENT.   *
*  RECEIVERS:                                      *
*    '67 EAC R-390/URR Surplus Receiver.           *
*    YAESU VR-5000 Wideband,  REALISTIC DX-392.    *
*    Home built Longwave "Hybrid" CW receiver.     *
*    Others which pass thru or are waiting repair. *
*  ANTENNAS:                                       *
*    Coil Loaded 18.5 Meter Long Sloper.           *
*    Roof mounted Hustler 6BTV 6 band Vertical.    *
*    Scantenna Scanner antenna at 7 Meters high.   *
*  LOCATION: Merced, Central California.           *
****************************************************




---
avast! Antivirus: Outbound message clean.
Virus Database (VPS): 7/10/2003
Tested on: 7/12/2003 6:32:04 PM
avast! is copyright (c) 2000-2003 ALWIL Software.
http://www.avast.com