Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Cobbler on July 04, 2016, 10:52:50 am
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I recently completed building a Hoffman Princeton Reverb. I used the cabinet, chassis, and speaker from an 70's vintage Peavey Backstage 30, scaled the board down a little to make things fit and also had to scrunch the tube together a bit.
Everything works great, no hum or buzz. I've been playing through it for an hour or two every day for the last couple months and have used it with the church choir a couple of times.
Thought I would try a couple different speakers to see what the sound difference would be. My stock of 10" speakers consists of a Rola, a Jensen, and a Cleveland taken from old organs that I have dismantled. All of these speakers work fine in other amplifiers and all read the same as the Peavey speaker on the multimeter but all of them produce a very loud hum as soon as the tube come up to temp.
This makes no sense to me at all. Any ideas?
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Have you tried putting the original peavey speaker back in and the hum goes away? I just think it seems unlikely that 3 out of 4 speakers has a hum, and instead something changed when you started swapping speakers, independent of the speakers themselves. If the peavey is quiet again, I'm not sure, but it may be more that somehow in adjusting the speakers you've accidentally moved/changed a connection somewhere so its not as solid and prone to noise?
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Put the Peavey speaker in, works fine.
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Is the peavey speaker in the chassis vs the others outside of it in some slightly different arrangement? Sometimes a single coil pickup can cause noise depending on how close it is to the amp and transformers, the positioning of the speaker that's in the cabinet is done to be, I think, more optimal, whereas the speakers you're testing may be closer to the chassis in a different orientation, inducing some noise from the transformers etc?
Or are you literally swapping them into the same location in the chassis?
YOu could try at least moving the non peavey speakers into slightly different locations a bit more away from the chassis?
~Phil
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I had the same theory, and no, it does not matter if it is in the proper place in the cab or outside for a quick test.
This is not a single coil hum...this is a very loud "something seriously wrong" type of hum. :dontknow:
Maybe its the cab/chassis fighting to retain its Peavey heritage :laugh:
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Maybe your Peavey speaker has lost it's bass response and the other speakers are actually revealing a problem with the amp?