Hello All,
For some reason the power transformer actually vibrates. There is a buzz like neon lamp radio interference in the sound. It's loud enough to be annoying at low volumes and in listening to classical music during quiet passages. How do I stop this buzz coming from the power transformer. Is it coming from the power transformer? I replaced all the paper and filter capacitors, I replaced the rectifier. The hum buck winding in the speaker transformer is good and connected correctly. If I try to add to either filter capacitor the buzz gets louder.
Is this a problem with the power transformer? How can I tell?

Thanks,

Dave

Dave,
Sometimes a couple of the laminations will get loose, and even under normal load will physically vibrate. Make sure all the mounting screws are tight and any case/cover is secure. Have you tested all the windings for DC resistance, shorts between windings and to case/laminations unpowered? Are all voltages correct? Is it overheating? Is there any indication of excess DC current on the load side?

marv

:Hello All,
: For some reason the power transformer actually vibrates. There is a buzz like neon lamp radio interference in the sound. It's loud enough to be annoying at low volumes and in listening to classical music during quiet passages. How do I stop this buzz coming from the power transformer. Is it coming from the power transformer? I replaced all the paper and filter capacitors, I replaced the rectifier. The hum buck winding in the speaker transformer is good and connected correctly. If I try to add to either filter capacitor the buzz gets louder.
: Is this a problem with the power transformer? How can I tell?
:
:Thanks,
:
:Dave

Marv,
The power supply voltages seem correct and the transformer doesn't get hot, as far as I can tell. I'll check it again. I haven't tried measuring the dc resistance of the transformer. This transformer doesn't have a cover. It just has laminations.

Thanks,

:Dave,
:Sometimes a couple of the laminations will get loose, and even under normal load will physically vibrate. Make sure all the mounting screws are tight and any case/cover is secure. Have you tested all the windings for DC resistance, shorts between windings and to case/laminations unpowered? Are all voltages correct? Is it overheating? Is there any indication of excess DC current on the load side?
:
:marv
:
::Hello All,
:: For some reason the power transformer actually vibrates. There is a buzz like neon lamp radio interference in the sound. It's loud enough to be annoying at low volumes and in listening to classical music during quiet passages. How do I stop this buzz coming from the power transformer. Is it coming from the power transformer? I replaced all the paper and filter capacitors, I replaced the rectifier. The hum buck winding in the speaker transformer is good and connected correctly. If I try to add to either filter capacitor the buzz gets louder.
:: Is this a problem with the power transformer? How can I tell?
::
::Thanks,
::
::Dave

Dave,
As I interpret your posts, the buzz in the audio (speaker) would indicate an electrical vs physical, although a physical vibration could be transferred electically to the audio system via microphonic
tube(s). I think more sophisticated troubleshooting is in order.

marv

:Marv,
: The power supply voltages seem correct and the transformer doesn't get hot, as far as I can tell. I'll check it again. I haven't tried measuring the dc resistance of the transformer. This transformer doesn't have a cover. It just has laminations.
:
:Thanks,
:
::Dave,
::Sometimes a couple of the laminations will get loose, and even under normal load will physically vibrate. Make sure all the mounting screws are tight and any case/cover is secure. Have you tested all the windings for DC resistance, shorts between windings and to case/laminations unpowered? Are all voltages correct? Is it overheating? Is there any indication of excess DC current on the load side?
::
::marv
::
:::Hello All,
::: For some reason the power transformer actually vibrates. There is a buzz like neon lamp radio interference in the sound. It's loud enough to be annoying at low volumes and in listening to classical music during quiet passages. How do I stop this buzz coming from the power transformer. Is it coming from the power transformer? I replaced all the paper and filter capacitors, I replaced the rectifier. The hum buck winding in the speaker transformer is good and connected correctly. If I try to add to either filter capacitor the buzz gets louder.
::: Is this a problem with the power transformer? How can I tell?
:::
:::Thanks,
:::
:::Dave

Marv,
I tried a new EL84 and the buzz doesn't go away. Also, this sound is very loud on the SW band. So loud that if it's receiving anything at all, it's masked by the hum (buzz), whatever it is.

Thanks,

Dave
:Dave,
:As I interpret your posts, the buzz in the audio (speaker) would indicate an electrical vs physical, although a physical vibration could be transferred electically to the audio system via microphonic
:tube(s). I think more sophisticated troubleshooting is in order.
:
:marv
:
::Marv,
:: The power supply voltages seem correct and the transformer doesn't get hot, as far as I can tell. I'll check it again. I haven't tried measuring the dc resistance of the transformer. This transformer doesn't have a cover. It just has laminations.
::
::Thanks,
::
:::Dave,
:::Sometimes a couple of the laminations will get loose, and even under normal load will physically vibrate. Make sure all the mounting screws are tight and any case/cover is secure. Have you tested all the windings for DC resistance, shorts between windings and to case/laminations unpowered? Are all voltages correct? Is it overheating? Is there any indication of excess DC current on the load side?
:::
:::marv
:::
::::Hello All,
:::: For some reason the power transformer actually vibrates. There is a buzz like neon lamp radio interference in the sound. It's loud enough to be annoying at low volumes and in listening to classical music during quiet passages. How do I stop this buzz coming from the power transformer. Is it coming from the power transformer? I replaced all the paper and filter capacitors, I replaced the rectifier. The hum buck winding in the speaker transformer is good and connected correctly. If I try to add to either filter capacitor the buzz gets louder.
:::: Is this a problem with the power transformer? How can I tell?
::::
::::Thanks,
::::
::::Dave

Is this a car radio or a house radio? If the buzz is in the audio and RF, then you need better filtering in the B supply, as well as in the vibrator section (buffer capacitor, resistors, etc.). If you are using a solid state 0Z4 in place of an original, you should bypass the diodes with .01 MFD 1000 volt capacitors (possibly less, though surges can get quite high in that circuit). I gutted my 0Z4 in my radio and fitted it with diodes. It does buzz a bit more. Bypassing with capacitors helps a lot. You can try larger or smaller values to see which ones work best.

Physical lamination vibration that cannot be cured by tightening the screws, can be cured by giving the transformer a few more layers of varnish. If you can, remove the transformer and dip it in good varnish (not old thick varnish...it must be nice and thin, though not too thin).

Speakers that are mounted too closely to transformers and motors will pick up hum from the devices, especially if the speakers are fitted with output transformers. Weller soldering irons induce a notable hum in speakers when held closely.

Other than that, if you are getting buzz through the RF, then you have other troubles, like Marv suggested. Your transformer could have an internal arc, or you could be picking up radio interference. Someone in my appartment building must have purchased wireless internet recently, because I am getting the most terrible hum in my radios on all local stations. However, the hum is just a 60 cycle hum, and doesn't seem to have any data noises to it. It could be from a fluorescent or a wall wart. I changed a flickering fluorescent in my stairwell (lazy land lady), but that didn't help. I even plugged my radio into a circuit that only has one outlet, and then removed all of the other fuses for my appartment. Still no help. It must be coming from another appartment. I have found that when the radio is unplugged, the noise tends to go away. I should listen on one of my Zenith portables to see if the noise can still be received, even when using batteries.

If you are having the same troubles, for one thing, if the radio stays on for any period of time once unplugged (remaining charge in electrolytics), unplug it and listen to see if the noise goes away (often cannot be done when electrodynamic speakers are used, since they instantly lose all of their magnetism, though sometimes a residual remains). If the noise does go away, build yourself a filter. Using two 100 mH chokes from Radio Shack works well. Use a .01 MFD capacitor either across the line side or the radio side, or both, depending on what works best. American Science and Surplus sells little line filters for $2 a piece. Peter seems to have luck with them, but I haven't had so much. It depends on the situation, I guess. If you want some, I can send you some.

Idealy your transformer should have an electrostatic shield. I've only come across a couple of radios with that feature, however. Hopefully your transformer isn't arcing internally. If you had a spair transformer at hand, you could temporarily operate the radio from it (doesn't have to have the same voltage as the original....can be a bit less, simply for listening purposes). Depending on the radio, you could also temporarily operate the radio directly from the AC line. You'd need a 6.3 volt source for the filaments, and a 5.0 volt source for the rectifier, if a 5.0 volt rectifier is used. Hum might be more, since you could only wire the rectifier for half-wave operation. Full power would, of course, not be achieved, but many radios would work alright from a 120 volt source.

T.

When wiring directly to the AC line, I say that you need external filament supply sources, because even if you disconnect the high voltage winding of your transformer, it may still arc inside, if it is arcing, or is otherwise causing trouble. You want the transformer to be completely off--no power going into it or out of it.

If the transformer is arcing inside, soaking it in varnish may cure the problem. Use thin varnish, and, for this purpose, allow the transformer to soak for a long time, so that all surfaces are penetrated. Then, of course, once you pull the transformer out, allow it to cure for at least 4 days. I'd say that it would be best to soak it for 24 hours at least. Make the varnish rather runny in this case.

T.

Thomas,
This is a house radio. I don't think that this is the problem anymore. Something has to be connected wrong. I hear only hum, and it gets progressively louder as it's tuned up in frequency on the SW band. Ihave moved on to another German set that has no sound on either AM band (BC or SW). Please see the other posting.
Whatever it is, it's inside the radio. No other radio I have here has these problems.

Thanks,

Dave
:Is this a car radio or a house radio? If the buzz is in the audio and RF, then you need better filtering in the B supply, as well as in the vibrator section (buffer capacitor, resistors, etc.). If you are using a solid state 0Z4 in place of an original, you should bypass the diodes with .01 MFD 1000 volt capacitors (possibly less, though surges can get quite high in that circuit). I gutted my 0Z4 in my radio and fitted it with diodes. It does buzz a bit more. Bypassing with capacitors helps a lot. You can try larger or smaller values to see which ones work best.
:
:Physical lamination vibration that cannot be cured by tightening the screws, can be cured by giving the transformer a few more layers of varnish. If you can, remove the transformer and dip it in good varnish (not old thick varnish...it must be nice and thin, though not too thin).
:
:Speakers that are mounted too closely to transformers and motors will pick up hum from the devices, especially if the speakers are fitted with output transformers. Weller soldering irons induce a notable hum in speakers when held closely.
:
:Other than that, if you are getting buzz through the RF, then you have other troubles, like Marv suggested. Your transformer could have an internal arc, or you could be picking up radio interference. Someone in my appartment building must have purchased wireless internet recently, because I am getting the most terrible hum in my radios on all local stations. However, the hum is just a 60 cycle hum, and doesn't seem to have any data noises to it. It could be from a fluorescent or a wall wart. I changed a flickering fluorescent in my stairwell (lazy land lady), but that didn't help. I even plugged my radio into a circuit that only has one outlet, and then removed all of the other fuses for my appartment. Still no help. It must be coming from another appartment. I have found that when the radio is unplugged, the noise tends to go away. I should listen on one of my Zenith portables to see if the noise can still be received, even when using batteries.
:
:If you are having the same troubles, for one thing, if the radio stays on for any period of time once unplugged (remaining charge in electrolytics), unplug it and listen to see if the noise goes away (often cannot be done when electrodynamic speakers are used, since they instantly lose all of their magnetism, though sometimes a residual remains). If the noise does go away, build yourself a filter. Using two 100 mH chokes from Radio Shack works well. Use a .01 MFD capacitor either across the line side or the radio side, or both, depending on what works best. American Science and Surplus sells little line filters for $2 a piece. Peter seems to have luck with them, but I haven't had so much. It depends on the situation, I guess. If you want some, I can send you some.
:
:Idealy your transformer should have an electrostatic shield. I've only come across a couple of radios with that feature, however. Hopefully your transformer isn't arcing internally. If you had a spair transformer at hand, you could temporarily operate the radio from it (doesn't have to have the same voltage as the original....can be a bit less, simply for listening purposes). Depending on the radio, you could also temporarily operate the radio directly from the AC line. You'd need a 6.3 volt source for the filaments, and a 5.0 volt source for the rectifier, if a 5.0 volt rectifier is used. Hum might be more, since you could only wire the rectifier for half-wave operation. Full power would, of course, not be achieved, but many radios would work alright from a 120 volt source.
:
:T.
:

Could be filtering troubles in the B current that goes to the RF section. Also, some radios respond differently than others to interference.

T.