I just received the radio, brought up the power, played well for about
five minutes, then the hum started, a noise like sizzling bacon, a
faint burning odor, then I shut off power immediately. Is it the
electrolytic capacitors, the rectifier, both? Any suggestions would
help.
Thanks,
Bob Grimes
--

Count Floyd wrote:
I just received the radio, brought up the power, played well for about
five minutes, then the hum started, a noise like sizzling bacon, a
faint burning odor, then I shut off power immediately. Is it the
electrolytic capacitors, the rectifier, both? Any suggestions would
help.
Thanks,
Bob Grimes


That is typical of an electrolytic capacitor that desperately needed for
you to spend a couple minutes of effort reforming it.

This is the one case where electrolytic capacitors fail shorted. The oxide
layer is too thin, and it arcs over, creating an electrolyte bridge between
the plates of the capacitor. All of the current goes into heating the
electrolyte, causing it to boil, and given time, spew forth from any weak
spot in the capacitor's case.

In spite of what a lot of the guys will tell you, bringing up the capacitors
on a variac doesn't help all that much. It's better than doing nothing,
but will still kill capacitors that could have been reformed. The reason
this is so, is when the capacitor is reforming, it inevitably creates little
short circuits. The variac doesn't limit the current, so when one of these
little shorts occur, it damages the aluminum foil.

A better way, with a tube radio, is to charge the capacitor up to operating voltage
using a bench power supply with a series resistor (2K, 5W). Because the tubes
aren't lit, there is little else in the circuit that will draw current while
you do this.

The capacitor, the rectifier tube, and possibly the transformer are
the likely collateral damage.

-Chuck

It's probably one of the three electrolytics in the can. Two are
the power supply filters, and the small value goes to the 6AQ5 audio
amp. I got a literal smoke test when I tested my HQ-145 and I saw the
smoke coming from the rectifier. I just recapped those three and the
receiver works fine now. The values in the can are not standard values
today, so I used a 47 and 60 mircro farad, 450 volt. I was able to get
the same value for the 50 volt audio electrolytic. Recapping was a one
week project to order and receive the caps and about 30 minutes to
install them. I also got a four or five post terminal soldering
strip, one of them grounded to place the caps. An ambitious person
could try to stuff the caps into the metal can in a rebuild, but that
is a bit too much authenticity for me. These 45 year old caps do dry
out. It might be possible to reform them with a Variac brought up
slowly, but I've never tried it. This is not a '64 Mustang
convertable or an ancient Corvette. My view is that even when new,
non-orignal parts were substituted in any routine repair.

Just remember to replace any jumpers on the relay outlet on the back
panel. The radio doesn't work without it. You either need the jumper
or a contact on a relay as I discovered in a very frustrating trouble
shooting session. Duh!

Jon W3JT


On Thu, 05 Jun 2008 16:07:39 GMT, "Count Floyd"
wrote:

I just received the radio, brought up the power, played well for about
five minutes, then the hum started, a noise like sizzling bacon, a
faint burning odor, then I shut off power immediately. Is it the
electrolytic capacitors, the rectifier, both? Any suggestions would
help.
Thanks,
Bob Grimes

"Count Floyd" wrote in message
news:BJ4mQCBKg9HM-pn2-ehcdEVgdZ2kp@localhost...
I just received the radio, brought up the power, played well for about
five minutes, then the hum started, a noise like sizzling bacon, a
faint burning odor, then I shut off power immediately. Is it the
electrolytic capacitors, the rectifier, both? Any suggestions would
help.
Thanks,
Bob Grimes

Bob, why did you do that

Electrolytics should have been changed, and fuse the
AC! A faint burning odor the is transformer overheating.

Pedro
--

"Chuck Harris" wrote in
message news
Count Floyd wrote:
I just received the radio, brought up the power, played
well for about
five minutes, then the hum started, a noise like sizzling
bacon, a faint burning odor, then I shut off power
immediately. Is it the electrolytic capacitors, the
rectifier, both? Any suggestions would help.
Thanks,
Bob Grimes


That is typical of an electrolytic capacitor that
desperately needed for
you to spend a couple minutes of effort reforming it.

This is the one case where electrolytic capacitors fail
shorted. The oxide
layer is too thin, and it arcs over, creating an
electrolyte bridge between
the plates of the capacitor. All of the current goes into
heating the
electrolyte, causing it to boil, and given time, spew
forth from any weak
spot in the capacitor's case.

In spite of what a lot of the guys will tell you, bringing
up the capacitors
on a variac doesn't help all that much. It's better than
doing nothing,
but will still kill capacitors that could have been
reformed. The reason
this is so, is when the capacitor is reforming, it
inevitably creates little
short circuits. The variac doesn't limit the current, so
when one of these
little shorts occur, it damages the aluminum foil.

A better way, with a tube radio, is to charge the
capacitor up to operating voltage
using a bench power supply with a series resistor (2K,
5W). Because the tubes
aren't lit, there is little else in the circuit that will
draw current while
you do this.

The capacitor, the rectifier tube, and possibly the
transformer are
the likely collateral damage.

-Chuck

Its easy enough to check the transformer. Remove the
rectifier and measure the AC voltage at the socket where the
plate pins connect. Actually, if the tranformer has shorted
it will probably make noise just having AC on it.
Electrolytic caps often have a strong ammonia-like odor when
the go short and often vent electrolyte. If yours have done
this clean the stuff off whatever its gotten on because it
can be corrosive.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Tio Pedro" wrote in message
...

One other idea. The burnt smell could be a resistor, and
might be the result of a failed component. My HQ-145
had a burnt resistor which was caused by the IF transformer
failure. Have examined the chassis to see if there are any
burnt parts?

Pete

On Thu, 5 Jun 2008 22:04:46 UTC, "Tio Pedro"
wrote:


"Tio Pedro" wrote in message
...

One other idea. The burnt smell could be a resistor, and
might be the result of a failed component. My HQ-145
had a burnt resistor which was caused by the IF transformer
failure. Have examined the chassis to see if there are any
burnt parts?

Pete
Pete,
Have not checked, I am trying to find someone in my area to recap and
fix the radio as it is really beautiful shape, all knobs, no
scratches, really great looks! I wish that I had the knowledge to fix
the radio.
Bob

"Count Floyd" wrote in message
news:BJ4mQCBKg9HM-pn2-b9dUd7dd4Ep4@localhost...
On Thu, 5 Jun 2008 22:04:46 UTC, "Tio Pedro"
wrote:


"Tio Pedro" wrote in message
...

One other idea. The burnt smell could be a resistor, and
might be the result of a failed component. My HQ-145
had a burnt resistor which was caused by the IF transformer
failure. Have examined the chassis to see if there are any
burnt parts?

Pete
Pete,
Have not checked, I am trying to find someone in my area to recap and
fix the radio as it is really beautiful shape, all knobs, no
scratches, really great looks! I wish that I had the knowledge to fix
the radio.
Bob

I'm sorry to hear you're having those problems
I hope it is a simple fix, good luck with it. Mine is
in a closet waiting to be gone through.

On 6/5/08 5:34 PM, in article BJ4mQCBKg9HM-pn2-b9dUd7dd4Ep4@localhost,
"Count Floyd" wrote:

On Thu, 5 Jun 2008 22:04:46 UTC, "Tio Pedro"
wrote:


"Tio Pedro" wrote in message
...

One other idea. The burnt smell could be a resistor, and
might be the result of a failed component. My HQ-145
had a burnt resistor which was caused by the IF transformer
failure. Have examined the chassis to see if there are any
burnt parts?

Pete
Pete,
Have not checked, I am trying to find someone in my area to recap and
fix the radio as it is really beautiful shape, all knobs, no
scratches, really great looks! I wish that I had the knowledge to fix
the radio.
Bob


Where do you live? Perhaps someone will volunteer.

Hello Bob:

I see that you are unfamiliar with servicing radios. Many of us have taught
ourselves - I know I did. Working on an old radio is straightforward and
logical. There are many books out there that cover most of what you need to
know. Then, it just comes to common sense and deductive reasoning.

Manuals for most radios are available for free on the internet, and together
with an old Radio Amateur Handbook you can pick up everything you need.

Basic test equipment includes a digital voltmeter that can be purchased for
a few dollars. A $25 grid dip meter can serve as a signal source.
Gradually, you can pick up a few items which make servicing much easier.
However, most of us started with minimum equipment.

The older servicing books from the late 30s and 40s are ideal because they
assume they tell you how to make your own equipment. As a matter of fact,
if you need to test a tube, you can build a tube tester from scratch in just
a few minutes. It will have wires going all over, but you will be able to
make simple tests.

With all the new test equipment becoming surplus, you can often pick up some
older equipment for nothing, or very close to it. Old Tektronix scopes are
often available for hauling away. Likewise older tube signal generators.

The beauty of the older radios is that they all work pretty much the same.
A Hammarlund HQ-120, sold before WW II, is the same basic radio as your
HQ-145. Learning to service one will give you all you need to know to
service the other. That is far different than the radios today.

As others have mentioned, you can remove the 5U4 and that should remove the
overload on the power transformer. If the radio does not hum or smoke after
the 5U4 is pulled, then the transformer is fine and a simple replacement of
the filter caps will probably get you back into business. And, as others
have mentioned, a fuse would be very helpful to prevent a catastrophe in the
event of a short.

Colin K7FM