I meant Dogbone caps, not horseshoe. Sheesh.
Hi Guys,
Here is an update on my T-4XC PTO adventure. I eventually removed the
PTO from the transmitter and put it in a panavise on my bench, powered
it up and listened to it on my TR-7 with a sniffer wire. While
monitoring the tone, I tapped on the rod that carries the ferrite
slug. It would make the frequency change and stay on the new frequency
every time I tapped it. As an experiment, I opened up the R-4C and
tapped on the end of the slug shaft on it. On the R-4C, the frequency
would change but always return to the original freq. To make a long
story short, I found hardened grease in the ball bearing races. I
cleaned the ball bearings, races and the drive screw with denatured
alcohol. The frequency returns to the same tone now every time I tap
it and the warbling is gone when I turn the knob. I was and am
convinced I fixed the problem.
Here is the part where Murphy rears his ugly head. I put the PTO back
together and reinstalled it in the T-4XC and
presto!!............what?.... dead silence. I used the PTO to control
the R-4C still ....dead silence. I checked power and ground it looks
fine but still, nary an oscillation from the PTO. So I unsoldered the
wires and hauled it's sorry a?!%#$ back onto the bench. Powered it up
and still nothing.
Obviously, I hosed it somehow during the re-install. I looked for a
solder problem around the output terminal it looked ok, but there were
a couple of strands of wire from the old connection that the solder
sucker (me) missed, but they weren't touching anything. Maybe they
were touching something when it was installed, I don't know.
At any rate, its dead now and I suspect a semiconductor. here are my
questions: (about time eh?)
I have the diodes in stock but not the FET or the buffer transistor.
If I have to make a Digikey (or Mouser) order anyway, maybe I should
just shot gun the thing and put in all new parts except the coils.
I also have a PTO from a parts rig that has issues. I would like to
rebuild it as well. Will I get into problems with tolerance stackups?
I suspect that is why there are "select at test" caps in there.
Can I replace the coax that goes from the PTO output to the wafer
switch with RG-174? (to give myself a small service loop, to make the
re-install easier)
If it turns out to be a cap, or if I shotgun it, is there a modern
replacement for those horseshoe caps?
Is there anything special about the temperature compensating caps,
like a backwards temp coefficient for bucking freq drift or something?
Is there an easy replacement for those?
Sorry for the long post about my epic struggle against the evil Murphy.
If the 49ers hadn't won, it truly would have been a lost weekend.
Thanks as always,
Bob K6GGO
Garey, Eddy, Paul, Curt and Steve,
Thanks for the quick replies guys. This is a great bunch on this
list. I am convinced that it is the PTO. If I lightly tap on the PTO
can with a pencil tip (and I mean very lightly) it causes the signal
to jump around. Maybe just a cold solder joint. I have a parts radio
(T-4XC) with a PTO in it. I guess I'll haul it out and test it. If
it's stable, I will swap it with the faulty one. Can I then rebuild
(shotgun) the bad PTO with all new parts? or is there special parts
in there that I have to be careful with? I probably have most of the
stuff in stock (NPO caps, metal film resistors etc.). It would be
handy to have a nice new spare because I also have a B-Line. Also, A
5Mhz PTO is a nice thing to have around, homebrew QRP rigs etc.
I have a HP signal generator, so I think I will try Paul's suggestion
on the Lissajous display. Perhaps I can find the faulty component
with some freeze spray and make this a quick repair. Maybe learn
something in the process (heaven forbid).
I wrote this e-mail in three sittings as real life keeps intervening.
The bottom line is, thanks for all the help, I will let you know how
I proceed and the results thereof.
73,
Bob K6GGO
On 2011-10-26, at 1:16 PM, Steve Wedge wrote:
Removing the PTO - at least with the A's and B's - requires removal
of the front panel. This is a good time to clean it as well as the
fiducial window. Use only dish soap for the window or you'll take
off the red line!
*/
/*
*/Hi Guys,/*
Well, I can not vouch for the "A" & "B" series, but in my T-4X
transmitter /that/extensive a dis-aasembly is most assuredly
*/NOT/*required...
After removing the three tubes immediately behind the PTO can, the
can itself is extricated by first dis-connecting the top grounding
spring, & then lightly squeezing together the "side prongs" that
hold the can in place, one prong at a time (this is by far the
/WORSE/part of the operation, and the most time-consuming).
The can is slipped off the assembly, rearward (where the 3 tubes were).
Next, with a pair of long needle-nose pliers, each brass spacer that
you see at the front of the vertical PTO board is grasped (so the
spacers won't fall & get lost), and a slotted screw driver is used
to unscrew the 4 screws that go through them. The PTO board & coil
assembly is now loose, save for the 3 wires that are attached to the
front vertical board: draw a simple sketch showing where these are
connected so that you'll remember when you re-assemble everything,
then touch each point on the board with a soldering iron to release
each wire...
The entire assembly is then slipped back off of the brass rod with
the ferrite slugs on it.
Absolutely /no need/to remove the front panel, no need for
/anything/that complicated, or involved...
To re-assemble, simply reverse this procedure! Hi Hi
*/~73~ de Eddy VE3CUI - VE3XZ/*
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