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Post subject: Vibrochamp Tremolo Driver
Posted: Sat Jan 07, 2012 4:34 pm
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Hey guys, I'm not trained in schematic reading. Could someone tell me which 12ax7 drives the tremolo on a silverface vibrochamp? I'm trying to do some tube taste-testing with the preamp signal tube and having trouble telling which is which.

Here is a link to the blackface schematic (which I think is the same or very similar to the silverface)

http://ampwares.com/schematics/champ_vibro_aa764.pdf


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Post subject: Re: Vibrochamp Tremolo Driver
Posted: Sat Jan 07, 2012 6:44 pm
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The second half of the 12AX7 connected to the Vibrato input (the half closest to the 5Y3GT rectifier). BTW... a good mica caps (I like Sprague 1KV rated type---the 0.02, 0.01, 0.01 mfd in a row), can make a difference, too. As much as the tube.


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Post subject: Re: Vibrochamp Tremolo Driver
Posted: Sun Jan 08, 2012 2:25 pm
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So to clarify (I'm a little dense), the tremolo driver is the 12ax7 on the left if you're looking at the back of the amp?


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Post subject: Re: Vibrochamp Tremolo Driver
Posted: Sun Jan 08, 2012 3:38 pm
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The tremolo uses the whole tube, not just half, and is the one closest to the output tube, second one from the right when looking at the back of the amp. The first tube on the right would be the preamp tube. :idea:

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Post subject: Re: Vibrochamp Tremolo Driver
Posted: Sun Jan 08, 2012 6:16 pm
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Go to the link you provided (or the one below is a little easier to see details). Scroll down to the layout section. The 0.02, 0.01, 0.01 mfd mica caps are off pin number 7, of V2 (12AX7). Also, I find changing the electrolytic bypass cap (off pin 3, of same tube)--- to a new Sprague 25mfd/50VDC can help a lot of the vibrato problems. I've tried the F&T 33mfd/160VDC cap as bypass off some of these tubes. They really make the vibrato deeper sounding. FWIW.

Make sure all the wires going to both the SPEED and INTENSITY pots are soldered well. And that the 100K-ohm off the SPEED pot is soldered to the back of the pot.

These circuits are pretty simple. A DVM to check continuity (esp to ground points) and voltages usually spots the culprit.

Good luck!

http://www.webphix.com/schematic%20heav ... _ab764.pdf

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