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On 2025-05-19 07:05, Mike W5RKL via groups.io wrote:

C145B, 60ufd 250VDC capacitor in C145 can. It didn't show a
short
with an ohm meter but under voltage it shorted

*** That's why I check electrolytics with an old-fashioned capacitor
checker. I have two - an old Heathkit with a magic eye tube, and a
Sprague TO-6. That purchase was inspired by our own Steve Wedge.

Either of these testers can perform leakage checks up to 600V or so.

- Jerry, KF6VB

Not only did C145B short internally under voltage but the capacitance
value of
C145B had increased from 60ufd to "108ufd", an "80% increase" in
capacitance
value, C145B in my TR3 not only took out TR3's R111 but it also took
out R4 in
the AC3 power supply resulting in complete loss of +250VDC LV supply.

If R192 in the TR4C is getting hot then it's quite possible C145A
20ufd can
capacitor is going bad. I agree, replace C145 can capacitor before it
takes
out R192 and quite possibly the AC power supply LV supply.

73
Mike W5RKL


On 5/19/25 8:21 AM, Steve Wedge, W1ES/4 via groups.io wrote:

If R192 in the TR-4C(any) appears heat stressed, check the can cap.
Replace R192 with the same value and wattage — it is a safety for
the MV. If you still have the original can, change it ASAP.

Steve Wedge, W1ES

Time flies like an arrow. Fruit flies like a banana.

Sent from Proton Mail [1] for iOS

On Sun, May 18, 2025 at 22:56, VE7PS via groups.io
<ve7ps@... [2]> wrote:
Interesting topic about the aging resistors in our 4-line gear.

Any time a rig comes into the shop ALL resistors get visibly
checked, but some get more attention than others.....

Here they are...

All PA screen and cathode resistors on the T-4X(any) and TR-4(any),
as we all know.

On the T4XC...R-81 and R91 in plate leads to V-9. Both are high
value resistors which tend to go high with time, reducing plate
voltage. If your audio drive seems low check these for sure. Also
check Plate Voltage on V-9, and if below spec, these resistors are
likely the reason. I found plate voltage on one T-4XC I fixed for a
friend years ago at +69VDC on V-9, while spec is +95VDC. R81 had
gone way high. Drakes aren't the only rigs I see this happening to.
K4OAH's "CD's" will help you locate the resistors, though that's
just the start of the fun! Frankly, ALL resistors with values above
200K or so deserve a resistance check. Doesn't seem to be as big an
issue on the B-line and earlier in this circuit as the circuits are
different and resistances are lower....cursory check though, so keep
that in mind.

Also on the T-4XC...R49 and R59 on the relay board. Often seen
heat-stressed.

On the TR-4C series...R 192 and R-45 on the relay board.

On all TR-4(any) - R163 on the 200 VDC line to the S meter. It
seems to act as a fuse and have found several visibly open!!!

I'm sure there are more, but this is a start. I'm sure there are
others who can add to the list.

73
Peter
VE7PS

On Sun, May 18, 2025 at 6:49?PM n4buq via groups.io [3] <n4buq=
[email protected]> wrote:

I have found that virtually all of the resistors in my TR-4 have
not aged out of tolerance which is a little surprising. I did,
though, replace the three 15R cathode resistors. I think one or two
were over 20 ohms but I replaced them mainly because they were no
longer all the same value.

Since R13 is "selected", then I presume one can read the bands and
should be able to check whether it's out of tolerance. At least R45
is not "selected".

Thanks for the tip!
Barry - N4BUQ (the other, other Barry)

Barry,
Something else to consider - Every TR-n that I've worked on has had
the plate current meter resistors aged high. The result is that
plate current measurement is not correct which of course means that
idle current is not set correctly. Seems to me that idle current is
the basic foundation for everything and if its not right than there
may be some odd things happen. There are two resistors. One is a
standard value and the other is determined by the Drake tech during
final alignment before the radio was shipped.

Also, I don't recall if you mentioned checking it or not but the
68ohm and 15ohm resistors under the amp tubes are also prone to
aging high. I always check and usually replace those resistors and
then measure the resistors for the meter and replace if they have
drifted. You can of course verify your idle current by measuring
resistance and voltage drop across the three resistors under the amp
tubes, calculating the current draw, and adding up the current draw
for all three.

73,
Another Barry
KJ5GQM

On Sunday, May 18, 2025 at 05:23:44 PM CDT, n4buq <
n4buq@...> wrote:

I tested all three tubes for gas and none were bad in that respect.
Interestingly, I decided to perform the "LIFE TEST" where the
filament voltage is reduced (I think it goes down to about 5.8V or
maybe 5.9V for a 6.3V filament). While transconductance drops by an
acceptable amount when that button is pressed, the fall in value
looked a lot like what I see for plate current when the key is down.

With all the tubes back in place, I decided to monitor the filament
voltage. I've been running the rig between 110VAC and 115VAC and
that was giving me a low-to-start-with filament voltage of just
under 6VAC. With that, key-down would cause that voltage to drop to
around 5.7VAC. I then bumped the autotransformer up to closer to
120VAC which gave me very close to 6.3VAC and, oddly enough, on
key-down, that voltage would drop just a small amount - perhaps
0.1VAC to 0.2VAC. That seems a bit odd that the sag was smaller
but, perhaps, the transformer is more efficient at the input voltage
closer to 120VAC but that's just a guess.

Also, with the input voltage closer to 120VAC, I think I'm seeing a
good increase in plate current at resonance. I suppose that's
expected since the plate voltage also climbs with that input
voltage.

Thanks,
Barry - N4BUQ

-------------------------

FROM: "Barry" < n4buq@...>
TO: "DRAKE-RADIO" < [email protected]>
SENT: Sunday, May 18, 2025 1:03:51 PM
SUBJECT: Re: [DRAKE-RADIO] TR-4 - Soft Finals?

Richard, Steve,
Thank you both for the responses. I wasn't sure if "soft" was just
a generic for "weak" and, in general, maybe that's true.
My three tubes do not exhibit some of the more obvious signs of
excess gas (e.g. white coating or a "getter-like" spot but that's
not a very good indicator of small gas amounts. I'm going to pull
them again and run the gas test as I didn't do that when I was
testing them. Maybe that will be revealing.
Thanks again,
Barry - N4BUQ

-------------------------

FROM: "Steve Wedge, W1ES/4 via groups.io [3]" <w1es=
[email protected]>
TO: "DRAKE-RADIO" < [email protected]>
SENT: Sunday, May 18, 2025 12:37:22 PM
SUBJECT: Re: [DRAKE-RADIO] TR-4 - Soft Finals?

Yep, that sounds like a textbook example. Power falls off first on
the higherbands as the gain (transconductance) decreases. The
electrons are generated at the heated cathode and eventually, the
cathode material gets depleted.

I’m starting to think that my TR-4Cw RIT is having similar
issues, though strangely, the output only sags when on the antenna
and not on the dummy load. The tubes in it are well-used.

Steve Wedge, W1ES

Time flies like an arrow. Fruit flies like a banana.

On Sat, May 17, 2025 at 10:46 PM, n4buq < n4buq@... [4]>
wrote: Can someone please tell me what is meant by the term "soft
finals"? I'm still having problems getting proper output from my
TR-4 and, for all I know, that might be the problem. I've tested
them for transconductance and all three are very close to the same
value and, furthermore, that value is quite a bit above the minimum
for a good tube.

Aside from low output (i.e. about 300 mA plate current maximum into
a dummy load), I notice that if I hold down the key for a few
seconds the plate current tends to drop just slightly and I think if
I were to continue holding the key down, the current would continue
to slowly decrease.

I measured the voltage across each cathode resistor and I notice the
same phenomenon: the voltage climbs to about 1.6 VDC and then begins
to drop a bit. Like the transconductance values, each cathode
resistor is "matched" in value and behavior to the other two so I
suppose that's one good thing.

Am I seeing the result of weak/soft tubes or is something else going
on that would cause this?

Thanks,
Barry - N4BUQ

Links:
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[5] /g/DRAKE-RADIO/message/84964
[6] /mt/113171093/243852
[7] /g/DRAKE-RADIO/post
[8] /g/DRAKE-RADIO/editsub/243852
[9]
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