I have a tube radio that I restored and got working again and it is one that I try to use most everyday. After about 3 months it developed a hum. I checked the electrolytics and they seem to have degraded since I installed them. So I replaced them again. No more hum. It has been about 4 months now on the newest electrolytics and I am again starting to hear it hum.

Could a bad amplifier or audio output tube somehow be doing nasty things to the electrolytics? I don't have a tube tester and all the other components are operating within expected tolerances.

Suzanne

Normally new current production electrolytics of a quality brand such as Sprague or Nichicon should last for many years in use. It's extremely rare for them to fail in just a few months. Is the voltage rating of the new caps adequate for the radio? Are the caps you are installing old stock from the 50's or 60's, or are they recent production?

Hi Suzanne

Are the replacements new manufacture? New electrolytic caps that have been around for 30 years or so will dry out and lose capacity.

Are voltage ratings high enough? If you notice any heating caps need to be replaced.

Norm

:I have a tube radio that I restored and got working again and it is one that I try to use most everyday. After about 3 months it developed a hum. I checked the electrolytics and they seem to have degraded since I installed them. So I replaced them again. No more hum. It has been about 4 months now on the newest electrolytics and I am again starting to hear it hum.
:
:Could a bad amplifier or audio output tube somehow be doing nasty things to the electrolytics? I don't have a tube tester and all the other components are operating within expected tolerances.
:
:Suzanne
:

Norm, c.,

Yes, the caps are always new manufacture caps. I've read too much about NOS caps and stay away from them. The voltage ratings are at 600V and they are only being asked to handle about 240V in the circuit.

I'll keep poking around and eventually get to the bottom of it.

Maybe its time to go back and double check the schematic against the chassis to make sure everything is in fact routed to the correct places.

Thanks guys,

Suzanne

:Hi Suzanne
:
: Are the replacements new manufacture? New electrolytic caps that have been around for 30 years or so will dry out and lose capacity.
:
: Are voltage ratings high enough? If you notice any heating caps need to be replaced.
:
:Norm
:
:
:
::I have a tube radio that I restored and got working again and it is one that I try to use most everyday. After about 3 months it developed a hum. I checked the electrolytics and they seem to have degraded since I installed them. So I replaced them again. No more hum. It has been about 4 months now on the newest electrolytics and I am again starting to hear it hum.
::
::Could a bad amplifier or audio output tube somehow be doing nasty things to the electrolytics? I don't have a tube tester and all the other components are operating within expected tolerances.
::
::Suzanne
::

Hi Suzanne

What values are your electrolytic caps? You mention using 600 volt rated caps. Electrolytic usually only go to 450 or 500 volts. Could your filter caps be lower capacity than originals?

Norm

:Norm, c.,
:
:Yes, the caps are always new manufacture caps. I've read too much about NOS caps and stay away from them. The voltage ratings are at 600V and they are only being asked to handle about 240V in the circuit.
:
:I'll keep poking around and eventually get to the bottom of it.
:
:Maybe its time to go back and double check the schematic against the chassis to make sure everything is in fact routed to the correct places.
:
:Thanks guys,
:
:Suzanne
:
:
::Hi Suzanne
::
:: Are the replacements new manufacture? New electrolytic caps that have been around for 30 years or so will dry out and lose capacity.
::
:: Are voltage ratings high enough? If you notice any heating caps need to be replaced.
::
::Norm
::
::
::
:::I have a tube radio that I restored and got working again and it is one that I try to use most everyday. After about 3 months it developed a hum. I checked the electrolytics and they seem to have degraded since I installed them. So I replaced them again. No more hum. It has been about 4 months now on the newest electrolytics and I am again starting to hear it hum.
:::
:::Could a bad amplifier or audio output tube somehow be doing nasty things to the electrolytics? I don't have a tube tester and all the other components are operating within expected tolerances.
:::
:::Suzanne
:::

Sorry Norm,

I was wrong. They are not 600V caps.

There are two 40uF caps rated at 450V and there is one 20uF cap rated at 25V. The radio is a Coronado (Gambles) 43-6927.

The house it came out of was a veritable Gambles museum. Everything from this radio, to the fridge, freezer, lawn and garden equip, hand tools, etc. came from the local Gambles store at least until it went out of business.

Suzanne

:Hi Suzanne
:
: What values are your electrolytic caps? You mention using 600 volt rated caps. Electrolytic usually only go to 450 or 500 volts. Could your filter caps be lower capacity than originals?
:
:Norm

Hi Sizanne

You used the right values. Might check the 6X5 rectifier. If the two sections aren't balanced or there is leakage could have some him.

Norm

:Sorry Norm,
:
:I was wrong. They are not 600V caps.
:
:There are two 40uF caps rated at 450V and there is one 20uF cap rated at 25V. The radio is a Coronado (Gambles) 43-6927.
:
:The house it came out of was a veritable Gambles museum. Everything from this radio, to the fridge, freezer, lawn and garden equip, hand tools, etc. came from the local Gambles store at least until it went out of business.
:
:Suzanne
:
:
::Hi Suzanne
::
:: What values are your electrolytic caps? You mention using 600 volt rated caps. Electrolytic usually only go to 450 or 500 volts. Could your filter caps be lower capacity than originals?
::
::Norm
:

:Hi Suzanne
:
: Are the replacements new manufacture? New electrolytic caps that have been around for 30 years or so will dry out and lose capacity.
:
: Are voltage ratings high enough? If you notice any heating caps need to be replaced.
:
:Norm
:
:
:
::I have a tube radio that I restored and got working again and it is one that I try to use most everyday. After about 3 months it developed a hum. I checked the electrolytics and they seem to have degraded since I installed them. So I replaced them again. No more hum. It has been about 4 months now on the newest electrolytics and I am again starting to hear it hum.
::
::Could a bad amplifier or audio output tube somehow be doing nasty things to the electrolytics? I don't have a tube tester and all the other components are operating within expected tolerances.
::
::Suzanne
::