Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on November 02, 2019, 02:36:35 am
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I built a vibrochamp tremelo inside my stereo SE 6BM8 based guitar amp/reel to reel conversion. Basicially the whole left channel is a vibrochamp.
Playing with the tremelo more I notice that with the tremelo intensity maxed the left channel is quieter. This happens even when the vibrato is turned off via the footswitch.
With the tremelo turned off I can use it's intensity control to turn the amp up and down a fair bit.
Also with the tremelo intensity maxed I see 230v on the plates of the 6BM8 triode!!
Intensity down - 92v
Same thing with the cathode voltage
up - 3.3V down - 1.3
I'm not familiar with the vibro champ tremelo otherwise but this seems wrong to me
I'll post the schematic again and go over the tremelo circuit again
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I can use it's intensity control to turn the amp up and down a fair bit.
1st time I ran across that was a GA8 build I did and used a GA5T trem circuit injected like you're doing. the trem was weak, but the guitar guys liked the "extra" gain feature :icon_biggrin:
since you're altering the bias at the driver tube, I wrote it off as "normal" for that design
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I guess it could be inherrant in the design.
However I don't know if the 6BM8 triode likes to see those voltages.
I had one crack at the base the other day , an old mullard. i was recording with the amp alot the previous evening. Also that power tube gets quite hot and microphonic.
Can anyone suggest any tweaks to the vibrochamp tremelo circuit, or the 6BM8 triode circuit that could help alleviate this?
The tremelo also makes a loud pop when switching. I have checked twice(and more than twice) to make sure everything is wired properly.
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suggest any tweaks
looking n guessing, you might try a coupling cap between you "T's", that should stop the gain feature, but guessing a cap between 2 R's might effect the trem signal some/a lot :dontknow: