Hi all. Please bear with me, another humming radio question. I bought an old philips tube radio 22rb281. Really nice little model. But it has a low hum. Loud enough to be annoying. I have replaced all filtercaps, the rectifier, i’ve also replaced the coupling caps in the amplifier stage. I’ve had hum in some amplifiers before and mostly its been filament hum, which i can remedy one way or another. Now i know from experience that this kind of hum disappears as soon as i switch off the power supply while the music ebbs away. Now with this thing the hum doesn’t disappear but ebbs away when i shut off the power. I’ve never experienced that before. I measured the voltages and that all looks okay. Can this be a faulty tube? Anyone had this before?
Some high-impedance node is playing antenna there. Could be a break in either signal path or ground.
So this is always present, even in phono?
You will find ground where R20, R32 and a few other components meet near the filter cap - presumably a direct chassis connection. (If you don't have service docs yet, a web search turned them up.) There are a few more points like that, make sure they're all good.
Signal wise, you can try the following:
Grab a piece of wire and short R23 at B4 (find C53, which shares the same ground). Hum still there?
Yes: Repeat with R27. Hum still there? (If not, check B4 heater ground (pin 4 + 2), R26, C46. If yes, no clue.)
No: Look for bad components or joints among R16 - C37 - R32.
Tube sockets are good?
So this is always present, even in phono?
You will find ground where R20, R32 and a few other components meet near the filter cap - presumably a direct chassis connection. (If you don't have service docs yet, a web search turned them up.) There are a few more points like that, make sure they're all good.
Signal wise, you can try the following:
Grab a piece of wire and short R23 at B4 (find C53, which shares the same ground). Hum still there?
Yes: Repeat with R27. Hum still there? (If not, check B4 heater ground (pin 4 + 2), R26, C46. If yes, no clue.)
No: Look for bad components or joints among R16 - C37 - R32.
Tube sockets are good?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.