I've got a couple of Bogen Challenger CHB-100 amps, that I play guitar though.
The problem I'm having, is power supply noise (hum). I've recapped the PS with 4 new 100uf 450v caps and replaced the can with 2 individual 22uf 450v caps.
It hums without the tubes, so I'm satisfied that it's the PS making the noise.
I've read that the doubler can be noisy, so if I have to live with it, then so be it, but if anyone else has experience making one quiet, I would love to hear.
Thanks guys/gals.
The problem I'm having, is power supply noise (hum). I've recapped the PS with 4 new 100uf 450v caps and replaced the can with 2 individual 22uf 450v caps.
It hums without the tubes, so I'm satisfied that it's the PS making the noise.
I've read that the doubler can be noisy, so if I have to live with it, then so be it, but if anyone else has experience making one quiet, I would love to hear.
Thanks guys/gals.
Last edited:
Dotneck
Thanks! Now that you mention it, it seems like an obvious answer. wish I woulda thought of that..... [emoji848]
There are holes in the chassis, so I could buy a tag strip and tap off the resister for the bias supply with another diode, and elevate it about 30v pretty easily.
It'll take a few days to get a tag strip, but I will definitely report back when I get the changes made.
Thanks again!
Thanks! Now that you mention it, it seems like an obvious answer. wish I woulda thought of that..... [emoji848]
There are holes in the chassis, so I could buy a tag strip and tap off the resister for the bias supply with another diode, and elevate it about 30v pretty easily.
It'll take a few days to get a tag strip, but I will definitely report back when I get the changes made.
Thanks again!
It hums without the tubes? Doesn't sound like heater issues, and not really like B+ filtering.
Perhaps OT too close to PT. But these amps were not hummy when new.
Perhaps OT too close to PT. But these amps were not hummy when new.
That^^^
Hums without tubes? If the power transformer and output transformer are close and their laminations are not at right angles, they can couple fields and hum.
Also, some power transformers naturally "hum" mechanically, which is a vibration conducted into the chassis, so it resounds.
Hum is not generic, there are MANY causes of hum, and each has its own cure. Adding filter caps will do nothing to cure heater hum, and grounding the heaters will do nothing to reduce power supply ripple.
SO you need to find out WHERE the hum is coming from before you try to cure it.
Hums without tubes? If the power transformer and output transformer are close and their laminations are not at right angles, they can couple fields and hum.
Also, some power transformers naturally "hum" mechanically, which is a vibration conducted into the chassis, so it resounds.
Hum is not generic, there are MANY causes of hum, and each has its own cure. Adding filter caps will do nothing to cure heater hum, and grounding the heaters will do nothing to reduce power supply ripple.
SO you need to find out WHERE the hum is coming from before you try to cure it.
Sorry guys, I just realized my typo. It hums without preamp tubes. Without any tubes, it's silent. Sorry for the mistake.
I do appreciate your help!!!
I do appreciate your help!!!
Still not clear. Is V3 preamp or not? It's gonna hum bad with V3 removed.
WHY?? did you post a link to a file which is NOT the CHB scheme but directs us to some other site? That's sometimes a link to malware. (I did not follow this one.)
The CHB schem is readily available. Here's one.
Did you re-cap the bias supply? Have you converted to 1-Ohm cathode resistors and measured all four cathode currents?
WHY?? did you post a link to a file which is NOT the CHB scheme but directs us to some other site? That's sometimes a link to malware. (I did not follow this one.)
The CHB schem is readily available. Here's one.
Did you re-cap the bias supply? Have you converted to 1-Ohm cathode resistors and measured all four cathode currents?
Attachments
Sorry. I thought I chose the image off my phone. It must have been too large.
V1 6eu7 preamp (2 channels)
V2 12ax7 drives tone stack and recovery
V3 6c4 phase inverter
V4-V7 7868 output tubes (PPP)
I did recap the bias supply.
The hum is louder with the preamp tubes installed, so heater noise sounds reasonable.
As you can tell, I'm new to vacuum tubes.
I've been experimenting/learning for just over a year now, but I've learned a lot from this forum! I really appreciate the help.
V1 6eu7 preamp (2 channels)
V2 12ax7 drives tone stack and recovery
V3 6c4 phase inverter
V4-V7 7868 output tubes (PPP)
I did recap the bias supply.
The hum is louder with the preamp tubes installed, so heater noise sounds reasonable.
As you can tell, I'm new to vacuum tubes.
I've been experimenting/learning for just over a year now, but I've learned a lot from this forum! I really appreciate the help.
Ok, I officially can't post a jpeg. I'll do some how to use a forum 101, and post a pick without falling on my face.....
Some days your the bat, some days your the ball!
Some days your the bat, some days your the ball!
Not sure what to think, The schematic in post 8 works on my pc, but not on my phone using tapatalk. (I used tapatalk to upload from my phone)
Guess I'll stick to using the pc to post pics.
Anyways...... now that I've trashed my own thread, I'll get back to finding the hum problem.
Guess I'll stick to using the pc to post pics.
Anyways...... now that I've trashed my own thread, I'll get back to finding the hum problem.
Try adjusting the balance control - no need for test equipment, just put ypur ear close to the speaker and adjust for minimum hum.
Cheers,
Ian
Cheers,
Ian
Hum louder with *which* preamp tubes installed? You may have one bad tube.
What do ALL the controls do to the hum? That may narrow-down to a specific area.
I don't see a balance control?
What do ALL the controls do to the hum? That may narrow-down to a specific area.
I don't see a balance control?
The hum is reasonable with just the power tubes. You have to be real close to the speaker to hear it.
When you install the 6c4 phase inverter in doubles in volume. The 12ax7 which feeds and recovers the tone stack doubles the intensity again, and the 6eu7 which is V1 brings in the normal high gain instrument amp noise that most non hi-fi amps seem to have. (Resistor noise?)
The bass and treble controls do nothing to the hum.
The volume controls all seem to control the hum. (V1 and V2 both are shielded tubes, and the amp will oscillate at certain volume levels without the shields in place, but the amp operates normally with them in place)
I've tried different tubes in all 3 preamp sockets. I only have 2 6eu7 tube and 2 6c4 tubes to play with, but I didn't figure the odds of all of them being bad was too high. I have 30 12ax7 tubes (salvaged an organ) so I've tried everything from Telefunken to Sylvania to Bogen, to RCA, to JJ, and it made no difference.
The hum balance pot is underneath. It's an all metal pot which the cathodes of the 7868s are tied to. Each pair of 7868 cathodes are tied together, and then ran to one side of the pot. The center/wiper is grounded to the chassis. I think it's value is 33ohms. Adjusting it per the owners manual (all volumes at 0) doesn't seem to make much difference.
I ordered some tag strips, and 1ohm resistors, so I can be ready to do individual output tube measurement, and dc heater elevation.
When you install the 6c4 phase inverter in doubles in volume. The 12ax7 which feeds and recovers the tone stack doubles the intensity again, and the 6eu7 which is V1 brings in the normal high gain instrument amp noise that most non hi-fi amps seem to have. (Resistor noise?)
The bass and treble controls do nothing to the hum.
The volume controls all seem to control the hum. (V1 and V2 both are shielded tubes, and the amp will oscillate at certain volume levels without the shields in place, but the amp operates normally with them in place)
I've tried different tubes in all 3 preamp sockets. I only have 2 6eu7 tube and 2 6c4 tubes to play with, but I didn't figure the odds of all of them being bad was too high. I have 30 12ax7 tubes (salvaged an organ) so I've tried everything from Telefunken to Sylvania to Bogen, to RCA, to JJ, and it made no difference.
The hum balance pot is underneath. It's an all metal pot which the cathodes of the 7868s are tied to. Each pair of 7868 cathodes are tied together, and then ran to one side of the pot. The center/wiper is grounded to the chassis. I think it's value is 33ohms. Adjusting it per the owners manual (all volumes at 0) doesn't seem to make much difference.
I ordered some tag strips, and 1ohm resistors, so I can be ready to do individual output tube measurement, and dc heater elevation.
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