I have been a 2-way radio technician for 29 years. I have seen examples of old tube type radios doing nothing but buzz, but have not seen the common reason for this other than replace all of the caps. Is there a common cap that causes this? A sweet old lady ask me to fix it for her. All the tubes check good on my antique tube tester.

Hi Mike

Electrolytic filter caps are usually responsible for hum in radios. They dry out over time and lose capacity or become leaky.

If it's a buzz or other noises quite often it's caused bt outside interference.

Norm

:I have been a 2-way radio technician for 29 years. I have seen examples of old tube type radios doing nothing but buzz, but have not seen the common reason for this other than replace all of the caps. Is there a common cap that causes this? A sweet old lady ask me to fix it for her. All the tubes check good on my antique tube tester.
:

Thank You for the reply Norm. It is a continuous loud AC hum or buzz that is not effected by volume control. Do I start with the biggest electrolytic's or the smallest?

:Hi Mike
:
: Electrolytic filter caps are usually responsible for hum in radios. They dry out over time and lose capacity or become leaky.
:
: If it's a buzz or other noises quite often it's caused bt outside interference.
:
:Norm
:
::I have been a 2-way radio technician for 29 years. I have seen examples of old tube type radios doing nothing but buzz, but have not seen the common reason for this other than replace all of the caps. Is there a common cap that causes this? A sweet old lady ask me to fix it for her. All the tubes check good on my antique tube tester.
::
:
:

Mike

That's power supply hum when it doesn't go away with volume turned down.

Tube radios often have a two or three section electrolytic cap. Usually values like 50/30 mf @ 150 volts or 40/60 mf @ 150 volts. Replace both or all three sections. Use modern values which will be 33, 47 mf @ 160 volts.

Norm

:Thank You for the reply Norm. It is a continuous loud AC hum or buzz that is not effected by volume control. Do I start with the biggest electrolytic's or the smallest?
:
::Hi Mike
::
:: Electrolytic filter caps are usually responsible for hum in radios. They dry out over time and lose capacity or become leaky.
::
:: If it's a buzz or other noises quite often it's caused bt outside interference.
::
::Norm
::
:::I have been a 2-way radio technician for 29 years. I have seen examples of old tube type radios doing nothing but buzz, but have not seen the common reason for this other than replace all of the caps. Is there a common cap that causes this? A sweet old lady ask me to fix it for her. All the tubes check good on my antique tube tester.
:::
::
::
:
:

Norm, that is what I thought on the power supply, thank you very much for confirming it. I will take a look at it, have a great eveining

:Mike
:
: That's power supply hum when it doesn't go away with volume turned down.
:
: Tube radios often have a two or three section electrolytic cap. Usually values like 50/30 mf @ 150 volts or 40/60 mf @ 150 volts. Replace both or all three sections. Use modern values which will be 33, 47 mf @ 160 volts.
:
:Norm
:
::Thank You for the reply Norm. It is a continuous loud AC hum or buzz that is not effected by volume control. Do I start with the biggest electrolytic's or the smallest?
::
:::Hi Mike
:::
::: Electrolytic filter caps are usually responsible for hum in radios. They dry out over time and lose capacity or become leaky.
:::
::: If it's a buzz or other noises quite often it's caused bt outside interference.
:::
:::Norm
:::
::::I have been a 2-way radio technician for 29 years. I have seen examples of old tube type radios doing nothing but buzz, but have not seen the common reason for this other than replace all of the caps. Is there a common cap that causes this? A sweet old lady ask me to fix it for her. All the tubes check good on my antique tube tester.
::::
:::
:::
::
::
:
:

Depending on the age of this radio, if it also has paper capacitors, these can (and often do) become leaky with age. Leakage on audio bypass caps can throw off bias in audio tubes, causing distortion and run-away current. Leaky tone capacitors (that bypass treble out of the audio) can consume excessive current, cause crackling if they are arcing, and even damage resistors and transformers if they short. In some radios there will be a tone capacitor from the 1st audio tube plate to B- that will look like a mica capacitor (rectangle encapsulated in bakelite), but this is usually actually paper inside. These often arc and cause crackling noises.

For good reliability and peace of mind for the sweet old lady, it's best to replace these capacitors. If the set uses ceramic disc capacitors, don't even bother replacing those. They almost never fail. For replacement capacitors you can use one of the metalized film types available from the major antique radio parts suppliers listed on this site. Also, if there is a capacitor across the line cord, and it's paper (not ceramic disc), replace this as well. When these arc over, they can go off like a 10-pack of firecrackers, and while the radio may work perfectly well forever more afterward, it may just give the sweet old lady a heart attack. (They typically do not short badly enough to cause a fire hazard, but merely blow to pieces until they are no longer part of the circuit.)

T.

Thank You T. and Norm, I received much more help and expertise than I expected, You guys rock!

:Depending on the age of this radio, if it also has paper capacitors, these can (and often do) become leaky with age. Leakage on audio bypass caps can throw off bias in audio tubes, causing distortion and run-away current. Leaky tone capacitors (that bypass treble out of the audio) can consume excessive current, cause crackling if they are arcing, and even damage resistors and transformers if they short. In some radios there will be a tone capacitor from the 1st audio tube plate to B- that will look like a mica capacitor (rectangle encapsulated in bakelite), but this is usually actually paper inside. These often arc and cause crackling noises.
:
:For good reliability and peace of mind for the sweet old lady, it's best to replace these capacitors. If the set uses ceramic disc capacitors, don't even bother replacing those. They almost never fail. For replacement capacitors you can use one of the metalized film types available from the major antique radio parts suppliers listed on this site. Also, if there is a capacitor across the line cord, and it's paper (not ceramic disc), replace this as well. When these arc over, they can go off like a 10-pack of firecrackers, and while the radio may work perfectly well forever more afterward, it may just give the sweet old lady a heart attack. (They typically do not short badly enough to cause a fire hazard, but merely blow to pieces until they are no longer part of the circuit.)
:
:T.
: