Annoying high frequency ringing from my 832 tube amp - diyAudio
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Old 22nd February 2009, 12:35 AM   #1
kuroguy is offline kuroguy  United States
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Default Annoying high frequency ringing from my 832 tube amp

My tube amp has developed an annoying high frequency ringing that is coming from the bell end on the left side of the Hammond power transformer. The link below is a photo of the amp and the power transformer is in the middle. If I touch the bell end very lightly the ringing stops. It is quite annoying and can be heard across the room. Has anybody experienced this and what would you suggest I do to stop it?Click the image to open in full size.
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Old 22nd February 2009, 12:58 AM   #2
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Default Re: Annoying high frequency ringing from my 832 tube amp

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Originally posted by kuroguy
My tube amp has developed an annoying high frequency ringing that is coming from the bell end on the left side of the Hammond power transformer. The link below is a photo of the amp and the power transformer is in the middle. If I touch the bell end very lightly the ringing stops. It is quite annoying and can be heard across the room. Has anybody experienced this and what would you suggest I do to stop it?Click the image to open in full size.

Screws are all tight?

BTW, that is BEAUTIFUL!!
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Old 22nd February 2009, 01:12 AM   #3
kuroguy is offline kuroguy  United States
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Checked earlier today and the screws are all tight, and thanks for the compliment. I really do love the sound of this amp (minus the new ringing). I'm thinking removing the bell end and adding some sort of damping material to the inside of the bell end. Any thoughts from anyone on what material or even doing that?
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Old 22nd February 2009, 08:50 PM   #4
kmaier is offline kmaier  United States
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Agreed.... very nice looking amp. When you say high-frequency ringing, any idea what frequency it is? Did it just start suddenly? Does it stop instantly when the power is turned off or die out as B+ drops?

Regards, KM
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Old 22nd February 2009, 10:48 PM   #5
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Noisy PT seem to be common with Hammond brand. I had that with mine (not as loud) and I solved it by using auto body repair kit. I happened to have some fiberglass resin and sheet leftover from other project so I used that on the inside surface of bell. I sanded it a bit so that it will cling onto metal surface and applied it with the sheet cut to size. The overall thickness is about 1/8" and it reduced the ringing to almost none. The PT still buzzes though. You can also use Bondo but make sure it's not too thick or the bell won't close.

The other option is to go with different brand as it is what I'm planning on doing. I don't think Hammond PTs are what they used to be anymore.
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Old 23rd February 2009, 12:01 AM   #6
kuroguy is offline kuroguy  United States
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I was thinking about mixing some 2 part epoxy and pouring a layer of about 3/32" thick on the inside of the offending bell end. My other option is to complain to Hammond about the ringing. I expected more from a $50 transformer. I guess I'll give Hammond an opportunity to make this right before resorting to the other option.
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Old 23rd February 2009, 01:53 AM   #7
kuroguy is offline kuroguy  United States
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Quote:
Originally posted by kmaier
Agreed.... very nice looking amp. When you say high-frequency ringing, any idea what frequency it is? Did it just start suddenly? Does it stop instantly when the power is turned off or die out as B+ drops?

Regards, KM

B+ is on a time delay and the ringing starts as soon as the B+ comes on. It stops as soon as the power is turned off. Definately coming from the power transformer and only the one side. Sounds like it is in the 10-12KC range.
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Old 23rd February 2009, 01:59 AM   #8
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Sounds like it is in the 10-12KC range.
Wonder if you could see anything on the b+ with a scope? Thats a very odd frequency.
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Old 23rd February 2009, 02:04 AM   #9
kuroguy is offline kuroguy  United States
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freq is just an estimate. I could be way off. I placed a piece of steel between the output transformer and the power transformer and the ringing didn't change. It only comes from one side and the amp is symmetrical, so I doubt it is picking up stray magnetic field from the output transformers.

I'll wait to see what Hammond says and then I think I'll try the epoxy on the inside of the bell end. Should be a real pain in the *** removing the transformer.
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Old 23rd February 2009, 08:27 AM   #10
kmaier is offline kmaier  United States
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Odd.... if it's induced from load, one would expect the ringing to be 60Hz or a harmonic thereof. Is the PT running hotter than before? Rectifiers and filter caps are okay? Be very interesting to see what you eventually find out.

Don't expect too much from Hammond... my brother had problems with extreme magnetic fields from 300 series PTs, only on one side... so bad that it would hold a screwdriver in place (buzzing of course) and disturbed the OPT from a good distance. Despite repeated emails to Hammond, they offered no advice, just typical marketing info saying everything is fine. He eventually swapped them out for Dynaclones, problems solved.

Regards, KM
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