Regarding the PTO Can "RFI GASKET", I don't think you will gain anything
from gasketing the shield. Gasketing of enclosures in the normal sense
isn't going to be the same at the frequency of the PTO as it is at VHF
where we commonly see it.
I think the idea is not to try to trap RF but to limit the magnetics
change due to any mechanical movement. A simple solid connection should
suffice. In any case, even if one were to gasket the base, the hole in
the back end is still there, so what would be gained?
If those little spring clips are broken, replace them with a simple "L"
bracket for a 4-40 machine screw.
FWIW
Curt
ne and Edward Swynar wrote:
Hi Steve,
Well, you are MOST fortunate that you've located a good source of "...parts"
PTOs there...!
The only potential problems there would be (A) finding an exact replacement
for yours (I understand that Drake, like other manufacturers, had occasion
to change things "...on the fly"), and/or (B) getting a replacement PTO with
the exact same woes (or worse) as yours there now...! Hi Hi.
Hopefully you'll hit the proverbial home run, however, & all will be well
again...
In the meanwhile, Garey HAS stated, repeatedly, his desire to locate an
"ailing" PTO, for dissectrion on his work/test bench...if you do happen to
find a good working replacement, you may wish to keep Garey in mind as a
potential benefactor for your "...excess"...!
Good luck there---and do please keep everyone posted as to your progress.
I've been mulling over some ideas re. an effective RFI "...gasket" here to
improve the bonding between the bottom of the shield can & its mating metal
surface, & seem to have settled upon the idea of a "string" of RG-59 coaxial
shield braid long enough to go about the perimeter of the shield can: I'm
thinking that I could then secure the braid to both surfaces---physically to
the can, electrically to the base---by tightening a plastic automotive
"chicken band" along the length of the braid...
Stay tuned...!
~73~ de Eddy VE3CUI - VE3XZ
******************************************
----- Original Message -----
From: "Steve Wedge" <w1es1...@earthlink.net>
To: "Diane and Edward Swynar" <deswy...@xplornet.ca>
Cc: <drakelist@zerobeat.net>; <k4...@mindspring.com>
Sent: Sunday, January 09, 2011 12:47 PM
Subject: Re: [Drakelist] R-4A PTO Woes
Thanks for all the good info, Eddy, and I did somewhat remember seeing
some
of your travails being posted on the board here.
It does seem that the culprit is likely to be the cover, as I can make it
change frequency by wiggling it. After again examining the knob per
Garrey's suggestion, I feel that it is tighter than the one on the
perfectly-working PTO on my T-4X Very little axial play (but there is
some
and it affects frequency).
It looks like I'll have to see if there's any way for me to tighten those
cover spring clips. I'm still curious about the raspiness, however.
I won't mess with it long in the radio - I think I've located a source of
a
couple of PTO's that were pulled from parts rigs, so that may be the
easier
(wimpy) way out.
I'll keep the list up to date.
73,
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom appended
thereto.
--------------------------------------------------
From: "Diane and Edward Swynar" <deswy...@xplornet.ca>
Sent: Sunday, January 09, 2011 8:55 AM
To: "Steve Wedge" <w1es1...@earthlink.net>
Cc: <drakelist@zerobeat.net>; <k4...@mindspring.com>
Subject: Re: [Drakelist] R-4A PTO Woes
Hi Steve,
Of course, take heed to initially eliminate "...the usual suspects" just
as
Garey suggests in finding the cause of your receiver PTO's raspiness &
instability...but sooner or later, you just *may* have to bite the
proverbial bullet & get inside of that PTO shield can to see exactly
"...what's what" therein...
Now, if anyone on the Reflector starting to read this has no issue(s)
whatsoever with the PTO(s) in their rigs, consider yourself
blessed!---and
feel free to delete this mesage before proceeding any further (it IS
rather
long).
My experiences with the PTO of my T-4X are pretty much well-documented
in
previous posts...but to summarize briefly, the signal from my
transmitter
PTO would intermittently become raspy and off-frequency, as well. After
bravely(!) removing the PTO cover---and the entire PTO circuit board
itself!---I first cleaned everything that I could see with isopropyl
rubbing
alcohol...no change.
I then replaced the zener diode therein...no change.
I next added the Drake-prescribed after-market grounding strap inside
the
PTO...no change.
Finally, I did a visual inspection of the solder traces on the board of
the
PTO, & discovered that one of the joints of the 3000-pfd. silver mica
capacitor there appeared to be "crystalized" (as in "cold") under a
magnifying glass. I ultimately removed this capacitor outright, &
replaced
it with a pair of 1500-pfd. s.m.'s in parallel.
Did that solve the issue...? YES, and NO. As long as the rig is allowed
to
thoroughly warm-up for about 1 to 2 hours, all seems well and
good---however, even after this "heat soak", there continue to be very
infrequent (but still there!) minor frequency "creeps" up in frequency
that
I can detect, of a few tenths of hertz (but no raspiness).
Now, I should point out that my Drake Twins are located in my basement,
where the average ambient room temperature hovers at 50F (+/-)---and I
cool
the 6JB6A finals of the T-4X by fanning air OUT of the enclosure. My
suspicion initially at this point was that any of the temperature
compensating capacitors (themselves almost a half century old now!)
inside
that PTO shield never really have much of a chance to really & truly
warm-up, as such, and were acting "flakey" in getting up to
speed---hence
the continued display of off & on drift. And so I pondered the
possibility
of installing a small 12-volt pilot lamp "heater" inside the can, to
speed
things up to a constant level of warmth...
This past week I proceeded to look into that notion, and started by
removing
the PTO cover. HELLO!!! the locking tabs on one side were NOT FULLY
SECURED
into the mounting holes! As well, I concluded that ANY "heater bulb"
entry
into the tight quarters of PTO shield would necessitate that wires be in
close proximity to the coil field---and I had no idea what the
consequences
that might have upon the dial calibration...and I really did NOT want to
find out, either!
So I simply replaced the can/cover, being extra careful this time that
the
locking tabs were engaged.
Now, fast forward to yesterday, when I stumbled upon this nugget in the
matter of ferrite-rod oscillator tank coils (as in Drake PTOs), which I
quote now from page 85 of Harry D. Hooton's (W6TYH) 1968 book entitled,
"SINGLE SIDE-BAND: THEORY AND PRACTICE"...
To whit: "IN ORDER TO MAINTAIN ITS HIGH-Q THE FERRITE-ROD COIL SHOULD BE
KEPT AWAY FROM THE METAL SHIELDING, BECAUSE IT IS QUITE SENSITIVE TO ANY
EXPANSION IN THE SHIELDING DUE TO HEAT. THE SHIELD BOX SHOULD BE
CONSTRUCTED
OF FAIRLY HEAVY-GAUGE ALUMINUM. UNLESS THE BOX SEAMS AND THE TOP AND
BOTTOM
PLATES MAINTAIN A GOOD ELECTRICAL CONNECTION DURING EXPANSION OF THE
METAL,
THE COIL FIELD WILL BE DISTURBED AND CAUSE THE OSCILLATOR FREQUENCY
SUDDENLY
TO INCREASE FROM TIME TO TIME."
Hmmm...
If it takes that little to adversely affect oscillator frequency, the
detrimental effect upon stability of one of the "ears" of one of the
locking
tabs being loose now makes sense to me---just as the fact that continual
removal & replacement of the can probably has a bearing upon shielding
integrity, that heretofore was not compromised in any way since the rig
left
Miamisburg in 1966!
I'm next going to try some sort of "RFI gasketing" scheme at the base of
the
PTO shield can, to ensure that there are no "cracks" in the shielding
that
could be affected by normal heating of the rig...
Steve, hopefully your problem might be traced to a simple need for a
clean-up of dried-up grease/dirt in the PTO mechanism. While my own
personal
"...journey of discovery" here with my PTO has been enlightening, I
wouldn't
particularly wish the trip I've been taking upon anyone else...! Hi Hi
~73~ de Eddy VE3CUI - VE3XZ
*****************************************
----- Original Message -----
From: "Steve Wedge" <w1es1...@earthlink.net>
To: "Diane and Edward Swynar" <deswy...@xplornet.ca>
Sent: Saturday, January 08, 2011 8:37 PM
Subject: Re: [Drakelist] R-4A PTO Woes
I tried to take it off when I cleaned the receiver, Eddy. Those
spring-loaded catches didn't want to cooperate, so I stopped. The PTO
was
removed in its entirety prior to my dunking and drying the rig (which
came
out pretty nice, otherwise after being pretty filthy).
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom
appended
thereto.
--------------------------------------------------
From: "Diane and Edward Swynar" <deswy...@xplornet.ca>
Sent: Saturday, January 08, 2011 6:17 PM
To: "Steve Wedge" <w1es1...@earthlink.net>; "Drake List"
<drakelist@zerobeat.net>
Subject: Re: [Drakelist] R-4A PTO Woes
Hi Steve,
Have you---or any previous owner(s) that you may be aware of---had
occasion
to take the PTO shield can/cover off more than once from that
receiver,
for
any reason...?
There is method to my madness in asking this---I'll explain more when
I
get
your answer...
~73~ de Eddy VE3CUI - VE3XZ
*****************************************************************
----- Original Message -----
From: Steve Wedge
To: Drake List
Sent: Saturday, January 08, 2011 5:52 PM
Subject: [Drakelist] R-4A PTO Woes
I've got my twins warmed up and continue to have problems with the
PTO
in
the R-4A. When controlling the set from the receiver, the CW tones
sound
raspy and the frequency tends to jump around. If I touch the shield,
I
can
make the pitch change. Pressing on the tuning knob also seems more
sensitive.
When I control the frequency from the T-4X, the notes sound beautiful
and
don't vary. It seems less sensitive to mechanical contact with the
knob
as
well.
Is there a way of tightening up the PTO? Why does everything sound
T-7-ish
when using the receiver's PTO and not the transmitter's?
TNX es 73,
Steve Wedge, W1ES/4
To be is to do - Socrates
To do is to be - Plato
Do be do be do. - Sinatra
All my computers have my signature with various pearls of wisdom
appended
thereto.
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