Herbert Hum

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I've tried every possible combination of isolation tricks and my new(to me) Herbert continues to present considerably more 60Htz hum than any of my other amps. The output transformer mechanically produces quite a loud hum as well, but when I switch from standby mode even with nothing plugged in and the levels down, the same frequency hum appears at the speakers. Anyone else have a similar situation? Suggestions?
Thanks much,
David
 
Anything in the room running with a variable rheostat - Lights, lamps, fans?
 
Thanks, I have killed any outside source of noise. I do have a light dimmer that I have to turn off when I'm playing. I'll check upstairs to be certain, but I'm pretty sure it's all clear....
 
Have you tried adjusting the hum trimmer ?

My Herbo is a bit noisy with humming on Ch. 2+ only.
 
I was curious about that... Not sure about the procedure and risks. I guess I could note the current position and tweak it a bit to see what happens. Hopefully it isn't a 'tech only' thing. I adjusted the bias without a problem, I was just hoping to hear from someone who had touched the hum trim..
Thanks!
 
those hum trim pots really never need touching.

have you recently rebiased the amp? biasing one a little hot will cause it to pick up some cyclic hum.

are you using anything in the way of a power conditioner, sharing an outlet, a hum-free or anything to break the ground loop? good speaker cable?

usually the most over looked and simple of things are the culprit. reason i asked about the lights is i had my garage converted into my music room/studio/man-cave and doing that, i had adjustable track lighting installed in the ceiling. while looking the ultimate of cool and cozy, it is crap for amps unless the lights are all the way up!

recheck your bias too. once you get into the 80% territory, you will pick up some noise, especially on an amp that are as hi-fi as a diezel that have very little filtering to begin with.

steve
 
Thanks Steve!
I'll re-check my bias, I did set it just a touch hot(32mA via Amp-Head Dual Bias Tester).
You are correct, the hum balance trim did nothing for me. I did notice that I had to separate my Uberschall head from the Herbert by a couple inches and a metal shelf when the Bogner is on to keep the noise down. Next stop will be driving a real grounding stake into the soil outside because my house's electrical is old and iffy.
 

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Somebody is a little anxious! I really wish it was solved, but I fine tuned the bias and verified the AC grounding with a visual inspection and circuit check meter. All is good. None of my other 3 amps are having issues. The hum appears as soon as 'run' is switched on, all levels down, loop block patched. This was present prior to re-tubing(it's what motivated my full re-tube, as well as just having a fresh start for a used amp). Sounds like a trip to a tech for me. Thanks everyone for your help!
Cheers,
David
 
I adjust the hum trimmer after every retube. Not all tubes react the same to heater voltage. If you say the trim pot
had no effect, maybe it's blown. On a DMM it should read around 50 Ohm with the arrow at the center of the sweep.
Also, it may not be a bad idea to visually inspect the filter caps for leakage. They can easily induce hum in the manner
you are referring to. Also, try a few new preamp tubes if the caps appear to be in working order and the trimmer reads normally.
 
Sweet! Thanks! I'll take a look when I get home today. Any chance of pointing me to the filter caps(are they the big electrolytics along the back?)
Cheers,
David
 
What was causing the hum/ I have an amp that does that and I found it to be just layout. When I put my fingers in a certain area near the power tubes it goes down considerably. I added some copper tape securely in the area nad it helped tremendously.
 
"What was causing the hum?"
Still looking for the culprit....
Not sure who put the "solved" addendum on the title.
I'm pretty sure my amp is not typical, so I wouldn't look for a model wide issue.
Electronics age/fail sometimes or perhaps it is still just environmental. The hunt goes on.
 
Underground":1na84ews said:
"What was causing the hum?"
Still looking for the culprit....
Not sure who put the "solved" addendum on the title.
I'm pretty sure my amp is not typical, so I wouldn't look for a model wide issue.
Electronics age/fail sometimes or perhaps it is still just environmental. The hunt goes on.
Click to expand...
Turn it upside down. Carefully move your finger around inside the chassis. See if you can find an area(usually near the power tube wiring) and see if that has an affect. Try moving some wires around with a chopstick. I solved a hum issue I had that way, but that was while the amp's volumes were on. My amp had a more than normal buzz/hum that I found to be electromagnetic with no volume. Still came through the speakers like yours.
 
Underground":zaotckjf said:
"What was causing the hum?"
Still looking for the culprit....
Not sure who put the "solved" addendum on the title.
I'm pretty sure my amp is not typical, so I wouldn't look for a model wide issue.
Electronics age/fail sometimes or perhaps it is still just environmental. The hunt goes on.
Click to expand...


Somebody removed -solved- from the title of the thread.

First question: Are You playing on bed room level ?
 
I'm playing in my basement studio through an Alex attenuator(-6dB), master vol at 9:00. I've measured SPLs around 100dB. So, yes, it's not performance levels(I don't need ear protection) but it's pretty freakin' loud. What is odd is the noise floor is way up(compared to any of my other amps) even with all the volumes down.
Thanks for peeking in Peter! And Thanks for the capacitor(s) and screws! They made it intact this time. You are most generous.
Many thanks,
David
 
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