Drake tr4c problem
 

I'm a fairly new owner to the Drake line...

Having a small problem with a tr4-c and was hoping someone could send me
in the right direction.

After TX (cw) when relay releases, the RX sounds some times muted but
still there, the S-meter will rise up the scale to about 40+ and the rx
freq is off a bit (like on the wrong sideband)

If I re-Key, all will return to normal...this problem will happen about
50% of the time... looks like relay is fine), but more like the mute
curcuit is hanging...??? AGC?

Can someone point to the right tube/area to check for this problem?
I'll have to get some tubes to swap out but don't want to get all at
this time.

Tks to all in advance

best holidays,
Tom

Drake tr4c problem
 

TJM wrote:
I'm a fairly new owner to the Drake line...

Having a small problem with a tr4-c and was hoping someone could send me
in the right direction.

After TX (cw) when relay releases, the RX sounds some times muted but
still there, the S-meter will rise up the scale to about 40+ and the rx
freq is off a bit (like on the wrong sideband)

If I re-Key, all will return to normal...this problem will happen about
50% of the time... looks like relay is fine), but more like the mute
curcuit is hanging...??? AGC?

Why do you say that it looks like the relay is fine? Have you tested
its contacts? Have you looked at its contacts? Just because it goes
kachunk doesn't mean it is doing its job. Every symptom you have described
is classic for T/R relay contact problems.

The contacts on T/R relays in tube radios often get corroded, smoky and
intermittent. The first trick is to rub a piece of paper soaked in 91%
isopropyl alcohol between each and every pair of contacts. operate the
relay manually so that the contacts close on the paper strip. Keep doing
this with fresh paper until the paper comes out clean. If the paper
tears, the contact is pitted, and will need to be burnished. Burnishing
is done with a piece of hardened sheet steel that has been ground on
a course grinding wheel to make scratches that are like a fine file. You
use it like a fine file.

Do not ever use emery paper, or sandpaper of any kind, on the contacts
of a relay. Don't use a file either.

-Chuck

Drake tr4c problem
 

Why do you say that it looks like the relay is fine? Have you tested
its contacts? Have you looked at its contacts? Just because it goes
kachunk doesn't mean it is doing its job. Every symptom you have described
is classic for T/R relay contact problems.

Hi Chuck,

I guess I should have been more specific...I pulled the relay.

I had pulled the relay and looked at it ( it's new as the tr4c was newly
rebuilt when I rec'd it ). took a few readings and all was ok without
power of course.

Anyway, I re-pulled the relay (thank goodness for sockets) and poped off
the plastic cover...
Using an old elmer trick for keys, I used a strip of a dollar bill and
some alcohol. After doing all the contacts, put back in.

Well, you were right! I just got done testing it and it looks good for
now... time will tell... no more problem after 15mins or so.

Thanks agn

best holidays,
Tom

Drake tr4c problem
 

TJM wrote:
Why do you say that it looks like the relay is fine? Have you tested
its contacts? Have you looked at its contacts? Just because it goes
kachunk doesn't mean it is doing its job. Every symptom you have
described
is classic for T/R relay contact problems.

Hi Chuck,

I guess I should have been more specific...I pulled the relay.

I had pulled the relay and looked at it ( it's new as the tr4c was newly
rebuilt when I rec'd it ). took a few readings and all was ok without
power of course.

Anyway, I re-pulled the relay (thank goodness for sockets) and poped off
the plastic cover...
Using an old elmer trick for keys, I used a strip of a dollar bill and
some alcohol. After doing all the contacts, put back in.

Well, you were right! I just got done testing it and it looks good for
now... time will tell... no more problem after 15mins or so.

Thanks agn

Hi Tom,

I have seen this problem many many times. The relays have contacts
that were designed to run at several amps, and we are using them for
microamps in some of these circuits. The contacts would self clean if
enough current was passing through them, but how much current do you
really need to switch a crystal oscillator from USB to LSB? A proper
signal relay would have gold plated silver contacts to help prevent this
problem. WECO relays used in the phone system were actually made so that
each actuation would make the contacts wipe against each other.

A dollar bill is made out of really terrific paper. It should be excellent
for cleaning contacts. I used to keep some cotton bond typing paper around
for the job, but laser printers have rendered such nice paper obsolete.

With any luck, you won't have to clean the contacts again for a couple
of years.

-Chuck

Drake tr4c problem
 

With any luck, you won't have to clean the contacts again for a
couple of years.

Group (and Chuck)

Well , back to the tubes...
The tr4c is fine till fully warmed than the problem comes back.

Recap;
After TX (cw) when relay releases, the RX sounds some times muted but
still there, the S-meter will rise up the scale to about 40+ and the
rx freq is off a bit (like on the wrong sideband)
If I re-Key, all will return to normal...this problem will happen
about 50% of the time... looks like relay is fine), but more like the
mute curcuit is hanging...???

Relay cleaned but problem pops up when fully warmed up after 20+ mins,
I'm going to pick up a new vox curcuit tube (6fq7) and replace to
eliminate that... will post results.

Tom

Drake tr4c problem
 

TJM wrote:
With any luck, you won't have to clean the contacts again for a
couple of years.

Group (and Chuck)

Well , back to the tubes...
The tr4c is fine till fully warmed than the problem comes back.

Recap;
After TX (cw) when relay releases, the RX sounds some times muted but
still there, the S-meter will rise up the scale to about 40+ and the
rx freq is off a bit (like on the wrong sideband)
If I re-Key, all will return to normal...this problem will happen
about 50% of the time... looks like relay is fine), but more like the
mute curcuit is hanging...???

Relay cleaned but problem pops up when fully warmed up after 20+ mins,
I'm going to pick up a new vox curcuit tube (6fq7) and replace to
eliminate that... will post results.

Darn!

I doubt it is a tube, start looking at electrolytic capacitors, and
resistance values. The old carbon composition resistors tend to drift
up over time, and electrolytics, well, they don't do so well with time.

-Chuck

Drake tr4c problem
 

Recap;

After TX (cw) when relay releases, the RX sounds some times muted but
still there, the S-meter will rise up the scale to about 40+ and the
rx freq is off a bit (like on the wrong sideband)
If I re-Key, all will return to normal...this problem will happen
about 50% of the time... looks like relay is fine), but more like the
mute curcuit is hanging...???

Relay cleaned but problem pops up when fully warmed up after 20+ mins,
I'm going to pick up a new vox curcuit tube (6fq7) and replace to eliminate that... will post results.

Well, VOX tube,6fq7, replaced ( boy, they can be costly ) along with two
others in same section without luck... back to the drawing board. I
thought it was going to be an easy swap. Will recheck relay and then on
to voltage checks ( seems like heat condition )

Tom

Drake tr4c problem
 

TJM wrote:
Recap;

After TX (cw) when relay releases, the RX sounds some times muted but
still there, the S-meter will rise up the scale to about 40+ and the
rx freq is off a bit (like on the wrong sideband)
If I re-Key, all will return to normal...this problem will happen
about 50% of the time... looks like relay is fine), but more like the
mute curcuit is hanging...???

Relay cleaned but problem pops up when fully warmed up after 20+ mins,
I'm going to pick up a new vox curcuit tube (6fq7) and replace to
eliminate that... will post results.

Well, VOX tube,6fq7, replaced ( boy, they can be costly ) along with two
others in same section without luck... back to the drawing board. I
thought it was going to be an easy swap. Will recheck relay and then on
to voltage checks ( seems like heat condition )

Tom

Hi Tom,

Don't forget to take a look at the cathode resistor bypass
electrolytics in the Vox/relay driver section. They don't stand up
well to the test of time. Typical values are 10uf 15V. When they go
bad, the T/R relay will start to conduct partially all the time, which
can make even good contacts iffy.

It is (as I said earlier) highly unlikely to be a tube. Tubes are usually
an all or nothing affair.

-Chuck

Drake tr4c problem
 

I have cleaned the original relay in several TR-4Cs without
success, Tom. Gary, K4OAH sent me the info on a fix.
You can get a plug-n-play replacement
that has gold contacts and works well for $17 plus
shipping from:

P&B R10-E1-Y4-V2.5K.

Mouser has them in stock 655-R10-E1Y4-V2.5K
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid= 214416&e_categoryid=155&e_pcodeid=65500

They solved my relay problems.

In the Drake TR-4 (no "C") and the TR-3,
the same relay will replace to
cheap white piece of junk Drake supplied,
though it must be soldered in.

P.S. "Hanging" relay is often a bad 6EV7.

Drake tr4c problem
 

I have cleaned the original relay in several TR-4Cs without
success, Tom. Gary, K4OAH sent me the info on a fix.
You can get a plug-n-play replacement
that has gold contacts and works well for $17 plus
shipping from:

P&B R10-E1-Y4-V2.5K.

Hi Gang,

Yes, that's what's in there now... I knew it was fairly new.
Digikey carries them also for about $16.

Anyway went back in and started to get some pin voltages on the Vox
circuit tubes... stupid me got a small shock ( not use to these tube
rigs! ) and went to repull the relay.

Had prev cleaned them and this time found a sheet of wet/dry paper 1000
grit... fiq I'd gently redo the contacts ( hell the relay is cheaper
than tubes! ).
While it was out I ran the relay by an outside power source... looked
like one or two of the contacts were mis-aligned... fiq I could get
another so I put on the Opti-visor and reset to what looked like the opt
setting for both contacts.

Well darn if it seems to be ok now! I'll put a relay on order but for
now after 2 1/2 hours its been FB

Happy Holidays
Tom aa2vk