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Henrik Gustafsson
([email protected])
10/16/2001 9:51 PM
Tremolux tremolo in a Deluxe Reverb
I have built a 2x6v6 amp based on the Deluxe Reverb schematics (AB868) but I removed the
normal channel and replaced the tremolo oscilator and the intensity pot with just a 50k resistor.
This is a combo amp and I'm using a 10" alnico speaker. I'm very happy with the sound but
sometimes I would like to add some tremolo.
I have heard people describing the Tremolux as the best sounding tremolo. I guess everybody
knows, but the Tremolux (6G9-B) is creating the tremolo by playing around with the bias instead of
using a VCR in a voltage divider after the preamp.
My problem is that the Tremolux is using a A voltage of 365V compared to the well knowed high
410V in the Deluxe Reverb. How could I change the Tremolux oscilator to make it work on 410V?
Any other thoughts about using this design?
Thanks!
/Henrik
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Matthew Springer
([email protected])
10/17/2001 12:20 AM
bias mod trem thoughts (long)
The oscillator layout and topology should be the same. Most fender circuits use a phase shift
oscillator with a cathode follower to buffer the sine output. The tremelo local oscillator than either
feeds a optoisolator (bigger blackface amps) or is fed into the output stage directly as a common
mode voltage. You shouldn't need many or maybe even any changes to the stock BF or tweed
oscillator IF you have a preamp tube available for the trem circuit.
The name bias modulation is a little misleading as the bias still stays where you put it, what you're
really doing is mixing in a common mode AC sine wave voltage with the AC differential mode guitar
input signal and the DC bias voltage. Since a push-pull pair rejects common mode inputs, a "bias
modulation trem" really just saturates the tube gain in time with the isolator.
The REAL problem is that if the intensity pot ever fails (usually by the wiper lifting off the pot), you
loose the DC bias voltage and the output tubes go into runaway.
If you use a 500k resistor tied across the intensity pot from the bias feed side to the wiper, you'll
always have path for the bias voltage even if the pot wiper fails.
I absolutely love the "bias mod" sound and basically will always build with this instead of the
optoisolator type trem. OSunds WAY better than the blackface choppy trem.
-Matthew
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Mark Knapp
([email protected])
10/17/2001 11:08 PM
Re: Tremolux tremolo in a Deluxe Reverb
http://www.firebottle.com/fireforum/fireBB.cgi?forum=gadc&thread=145775
... 10/18/2001
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Page 2 of 2
Henrik, look at a 6G16 Vibroverb circuit:
http://www.fenderholic.com/schem/vibroverb_6g16_schem.gif
This is the immediate precursor to the BF amp, but notice the trem circuit. This is the place to start
when adding trem to your amp. I used this in my Bandmaster Reverb, though I ended up changing
the 470K coupling resistor to 180K to get enough trem. Now the thing thumps noticably with no
signal, though I haven't taken the time to work on that yet. I also haven't tried loading the signal
down to simulate the "roach" being there. I wonder if that makes the amp smoother?
Personally, I would like to try a three-tube Brown era tremelo. Maybe someday....
Mark Knapp
http://www.firebottle.com/fireforum/fireBB.cgi?forum=gadc&thread=145775
... 10/18/2001