Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mageerc on September 19, 2013, 08:01:25 am
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I have a Victoria 45410-T on the bench making a static type noise only in the Brite channel. This amp is based on the Fender Bassman 5F6A. The noise is not loud static, but rather it sounds muffled like it's in the distance. Here's what I have done so far:
Cleaned all the tube sockets
Cleaned and lubed all the pots
Burnished the shorting mechanisms on the input jacks
Substituted known good tubes, both power and preamps
Touched up all the solder joints in the Brite circuit
The noise still persists... Could this be a capacitor in that circuit trying to fail? There is a silver mica in that circuit and several orange drops...
Unfortunately my scope bit the dust last week, so I don't have that option to check with.
The Normal channel is fine and the noise is only in the Brite channel.
Any suggestions?
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I'd try changing the plate R's for the preamp an PI tubes next.
They can make noise after time. Sometimes even when new you can get a bad 1.
Brad :icon_biggrin:
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I don't know if the static is the reason the customer brought it in for or a problem you discovered after you got it on your bench testing it. If it's a problem you discovered after you got it, try plugging it into another wall outlet or a different guitar cord.
One time on a Silvertone 1482 I had a cathode resistor make noise like that and changing the cathode resistor corrected it but never had the cathode resistor do that on any other amp.
It sounds like a preamp tube to me, but you've already tried a different tube? Plate
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This was a phantom problem and the static sound was really odd like ocean waves off in the distance... not that loud but quite noticeable in a quiet room. It turns out the board was conductive made of the same fiber type board Fender used. The 68K grid resistors in the Brite channel were mounted on the on the board a scant 1/4" from the 100K plate load resistors for V1 and V2. I measured trace voltage in the space between. I moved the 68Ks to the input jacks like the Blackface amps were done and ran a new wire and the problem was gone!
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Wow! Your good. :icon_biggrin:
I would have chased my tail on that for a long time.
Marks amp are very good IMO. I know he went with the old black fiber board so it was just like an old Fender but I don't trust them.
How old is it?
Brad :icon_biggrin:
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It turns out it was a very early 45410 within the first year of manufacture. I called Mark after I figured it out and he told me I should have called earlier, that they had found that to be a problem a while back and had changed many things about the amp over the years to address these problems. We had a nice discussion and he was very helpful and informed.
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Yeah he's a nice guy, I have talked with him a few times.
Did he say what they did to the amps? You can move all the parts you want but if the board itself is the problem then you have to change the board.
It was a selling point to go with what Leo used.
Brad :icon_biggrin:
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As far as that particular problem, he said that they no longer mount the grid resistors on the board... he said they mount them on the input jacks like the Blackfaces. He mentioned that they spec some different components like Belton tube sockets instead of the black phonelic ones like were in this amp (I had to repair one of those sockets as a pin had gotten too hot and broke). He didn't mention that many other changes, but I didn't want to take up him time...
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Thanks was just wondering.
Brad :icon_biggrin:
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Yeah, wouldn't have guessed that either! One to mark down in the books for any fiber board encounters. Platefire