Hello All,
I have an old Heathkit tube amp which is all original and was working OK. Couple of days ago I noticed some noise on left channel.
The noise is like a rumble. Like a thunder but very low. Left channel only. The volume control does NOT affect the noise. The noise pattern is like 5-10 sec of silence then 2-3 seconds noise.
I moved all tubes around (swapped left/right) - and it still comes from left channel.
The mono/stereo/reversedstereo/reversedmono does NOT affect the noise.
Do you think this is a transformer?
I have an old Heathkit tube amp which is all original and was working OK. Couple of days ago I noticed some noise on left channel.
The noise is like a rumble. Like a thunder but very low. Left channel only. The volume control does NOT affect the noise. The noise pattern is like 5-10 sec of silence then 2-3 seconds noise.
I moved all tubes around (swapped left/right) - and it still comes from left channel.
The mono/stereo/reversedstereo/reversedmono does NOT affect the noise.
Do you think this is a transformer?
Doubtful. Far more likely to be a coupling cap, a bypass cap, or a solder joint in the left power amp section.
Before pulling her apart, swap output tubes. If the rumble is still in the left channel, look for bad solder joints and/or recap. If it switches channels, new tubes.
Geek said:
I did that. It is still in the left channel.
p.s. I would be so happy if it was a tube ;-) Cheap and easy to replace.
Hi Zepplock,
The louder the noise is, the closer to the input of the amplifier stage is will generally be. Don't discount the old carbon composition resistors for making noise either.
There are two tests you can make here. The first is to measure the ends of each coupling cap. The side going to the grid of the next tube should measure 0 VDC, within mV. The other test is to measure the resistor values after the supplies are discharged. You may find some out of tolerance. Take the time to match the 47K phase splitter resistors. Replace the parts that are out of tolerance.
I'd be replacing the coupling capacitors anyway if I were you.
-Chris
The louder the noise is, the closer to the input of the amplifier stage is will generally be. Don't discount the old carbon composition resistors for making noise either.
There are two tests you can make here. The first is to measure the ends of each coupling cap. The side going to the grid of the next tube should measure 0 VDC, within mV. The other test is to measure the resistor values after the supplies are discharged. You may find some out of tolerance. Take the time to match the 47K phase splitter resistors. Replace the parts that are out of tolerance.
I'd be replacing the coupling capacitors anyway if I were you.
-Chris
I second that! I have seen resistors make a rumbling or frying sound. It can also be a tube socket, but those will usually behave for a few days after changing the tubes.
You say that the function switch does not affect the noise, so that puts the problem in the area of the 6AN8 or the 6BQ5's.
The coupling caps are C19 and C21 for A channel and C44 and C45 for B channel. If they have never been replaced I would change them. The health of your output tubes depends on them.
I have often been able to find intermittent resistors with "freeze spray", although the freeze spray is getting hard to find. When the amp is making the noise, CAREFULLY spray each resistor one at a time, and wait for a few seconds. Often the bad resistor will behave when it is thermally shocked.
List of suspects: R24, R25, R26, R28, R30. Also the same resistors in the other channel. It is not clear from the schematic which is the left channel.
What you are describing SURE sounds like a solder joint or resistor. It is behaving exactly like the old blinker relays for turn signals. Heat from current causes the joint to open... once it opens the current wanes... as does the heat... and the joint reconnects. It could even be a tube socket... likely that would have a more severe impact on sound though.
Anatech is dead on the money, recap that old dog regardless; if you wish to keep it. Failing caps can fry transformers, tubes, all sorts of things. If you are SERIOUS, we can make a list of the caps you should service.
Caps died in my Leslie amp/speaker not too long ago... I had it unplugged in about 1/2 a second.
2nd Edit: I can't type in lttle boxes!!!!!!!!!!!!😡
Anatech is dead on the money, recap that old dog regardless; if you wish to keep it. Failing caps can fry transformers, tubes, all sorts of things. If you are SERIOUS, we can make a list of the caps you should service.
Caps died in my Leslie amp/speaker not too long ago... I had it unplugged in about 1/2 a second.
2nd Edit: I can't type in lttle boxes!!!!!!!!!!!!😡
Hi poobah,
-Chris
I'm sure we can find you some bigger boxes to type in. We didn't think of wookies, sorry. Why would you want to type in a little box anyway??
-Chris
It seems that I can never see the missing words, words I type twice, spelling... until I post!
🙄 🙄 🙄 😡 😡 😡
🙄 🙄 🙄 😡 😡 😡
Hi poobah,
Me too!
But I have an excuse, what's yours? 😀
Cut 'n paste into your email client. Spellcheck.
You can tell when I don't do that, aside from my reply coming much faster!
Me too!
But I have an excuse, what's yours? 😀
Cut 'n paste into your email client. Spellcheck.
You can tell when I don't do that, aside from my reply coming much faster!
Ok. I get the point.
First I really like the sound of this amp.
So sweet sound for Beatles/Led Zeppelin music ;-)
I'll try to replace ALL components around 6BQ5/6AN8.
And then (later) probably renew the tubes too.
Do you have any suggestions on which components I should use? I'd prefer to buy all from single online vendor or a fellow DIY'er ;-)
First I really like the sound of this amp.
So sweet sound for Beatles/Led Zeppelin music ;-)
I'll try to replace ALL components around 6BQ5/6AN8.
And then (later) probably renew the tubes too.
Do you have any suggestions on which components I should use? I'd prefer to buy all from single online vendor or a fellow DIY'er ;-)
Can you post some pictures? One of the top, and one of the bottom.
You should replace all of the electrolytics... you dont HAVE to; but you should.
You may need to replace some resistors as well... you have to measure/test them. Or, you can choose to replace most of them "just on principle".
😉
You should replace all of the electrolytics... you dont HAVE to; but you should.
You may need to replace some resistors as well... you have to measure/test them. Or, you can choose to replace most of them "just on principle".
😉
Hi Zepplock,
I normally use metal oxide resistors, 1 W minimum. Look at the voltage ratings to see if you need to go up in wattage.
Any axial film type capacitor will be better than what is in there. You may find yourself using two vendors. Digikey has amazing shipping.
-Chris
I normally use metal oxide resistors, 1 W minimum. Look at the voltage ratings to see if you need to go up in wattage.
Any axial film type capacitor will be better than what is in there. You may find yourself using two vendors. Digikey has amazing shipping.
-Chris
Kool. I'm waiting for my new DMM delivered next week. I'll open the amp to take measurements and get a list of components to replace.
Thanks you guys.
Thanks you guys.
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