Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: vampwizzard on November 04, 2020, 04:26:47 pm
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Starting to get a reputation as a person to bring amps to! SF Vibro Champ. Allegedly sat in a barn for several years.
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Young guitarist wants to gig it. Ill recap and cut out the death cap. 3 prong cord is otherwise wired correctly. Going with replacement cap can.. worth the price to keep it looking original. going with the 4x 20uf can in case he ever wants it modded/wired like the AB circuit. Ill be doing SF bypass caps.
Came with some cool tubes. 6V6 is probably bad. Fender labeled 12AX7s look ok though.
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that's definitely NOT from my barn, looks like fun
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My first time yanking out one of those big filter cap cans and that was a doozey. Worked out alright. Swapped out all the electrolytics, yokined the death cap, buttoned it up, found some fresh tubes, and turned it on. One second in I discovered the likely reason it went to the barn: the telltale sizzle and smell of a burning power transformer. Doubled checked all the incoming wiring and it was good. Checked the fuse value they had. 5A instead of 1 or 2A.
Grumble grumble.
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Well. Despite its wiring diagram, the hammond 290AX comes with the heater center tap and a vibro champ is wired serially with no center tap. Does it make that much a difference to wire it like the original without the center tap connected? Id rather not redo all that heater wire if I dont have to.
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Well. Despite its wiring diagram, the hammond 290AX comes with the heater center tap
You sure 'bout that?
Ahhhh...I see. Here's the new updated version:
https://www.hammfg.com/files/parts/pdf/290AX.pdf
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LOL yup its sitting up on the desk :laugh: :laugh:
Im probably just going to wire it up the way they made it at the factory and let the owner make the decision. Hes thinking about a speaker change.. thats when the noise will really become apparent. Ive got the extra filtering node available from the new cap as well so surely I can get it quiet.
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Im a newbie but I used the 290ax center taps on my AA1164 and I think it’s pretty darn quiet.
I don’t think you have to fully redo the heater wiring. It’s just removing the two 100ohms on the pilot light that create the artificial CT. At least that’s all I did. Champ circuit maybe different though.
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It’s different on the champ. No artificial center tap. One pin of the heaters is grounded as is one of the green line legs of the heater winding.
Wired it up like the original and while it’s a little hummy it’s not too bad really. Perfectly fine.
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Wired it up like the original and while it’s a little hummy it’s not too bad really. Perfectly fine.
It'll be mo betta if you take the time to rewire it. Should be able to measure the difference with ac voltmeter across the speaker.
Having said that, I left the filament wiring alone in my Harvard 5F10 when I replaced the PT. :wink:
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I rewired my Vibro Champ's heaters, the PT had been replaced with a PT that had a filament CT. The filament wiring was wired as original not using the CT. Some hum but not too bad, since the new PT had a filament CT, I figured use it and did, now quite as a dead man. :icon_biggrin: