Q... With the tremolo off how much gain is generated by the mixer portion of the trem? I only need to drive a 6BQ5 and I was wondering if I would need a stage after the tremolo mixer as a driver or is there enough gain here to do the job? Also, does this trem sound better with the overdrive coming before or after? A... you need some gain after the driver IMHO. The mixer passes a pretty weak signal, a couple volts. You need maybe 10+ to relaly drive a pair of EL84's decently. As for OD, I'd go before the trem myself. There are oddball LFO components left in the output from the mixer (no, it doesn't cancel all that well, which is *why* it works. :-) I think they'd make a mess out of an OD pedal. Also, you should IMO consider a HPF setup pre-power amp.. I used a Vox-style 3 pole HPF to lose the LF partials. (don't want them in the output circuit).. or you could use a single op-amp.. whatever works! It's a neat circuit. My best advice is to build it (build the whole Concert 6G12-A right up to the phase inverter (just that one channel) and then play with it. There's a lot going on in that circuit. Get a resistor sub box, a couple cap sub boxes and just go nuts. It's neat stuff. Esp the Rk on the mixer. You can see how they dialed it all in. (eg I think it sounds the best just the way it is!) I was trying figure out a way to get fancy schmancy and have some high gain preamp cunch in this little amp. But I think I'm going to have to go "vintage style". There are only four spots for 12ax7s and two and a half of those are trem. (I already cut a hole for one and don't feel like doing another.) I'm going to use the stage on the other side of the trem's phase splitter for the driver stage. It's single single ended el84 so a single gain stage should work, no? I'm not sure what you are refering to regarding the Vox HPF. I've built a top boost ac30 clone and don't remember anything special. Are you talking about the tone stack setup? I was planning on a bax type tone stack just before the power tube, but now that I'm not going so high gain maybe a standard Vox or Fender type would do. BTW got any leads/recommendations for sub boxes? I seem to be progressing from the tweak/repair mode to designing and building stuff from scratch. I'm such an empiricist that I have try EVERYTHING. (Circuit modelling on a Mac SUCKS!) When I first started looking at this circuit I was wondering about the possibility of putting a pot betweem the 1 meg resistors that go to ground after the phase splitter. CT of the pot to ground. I was wondering if this would essentially shift the bias of the tremolo so that it would, at one extreme, modulate only highs and at the other extreme only bass. I think it was you who told me that it wouldn't be this simple. 10 meg pot! Sheesh. I'm gonna use a rotary switch and a 3 meg pot to do Range and Fine controls. Also, I've been using the Brown Super as my model, and I noticed some differences in component values between the amps that used this topology. Does one stand out as definitively better than any other? Looking at the schematic, the brown tremelo circuit uses 2 1/2 tubes, 1 1/2 for an oscillator with two (out of phase) outputs and 1 tube for a frequency divider mixer circuit. I was wondering if anyone has given any thought replacing the oscillator section of that circuit with a few op amps, but maintaining the tube signal path. As an aside, any thoughts as to why the mixer tube in that circuit is biased so cold? (4k7 bias resistor on a 12ax7 tube) Very astute observation! This bugged me as well.. I was trying to get more signal through the effect and bump up the S/N ration and this was an obvious place to go. Thing is, that mixer being biased into a non-linear range is the *key* to the effect. Put a R sub box in there and watch the magic fade away was you go back to 820-ohms. It's dramatic. I have thought about replacing the osc with something SS.. maybe even a function generator with various waveforms etc. Could be fun, just never got round to it. CTS can still make the 10M-RA pots if you could get enough interest in building them.. otherwise a rotary switch would work (maybe inconjunction with a regular 3.5M-RA pot?) I would leave the amp stock overall, just up the value of the neg feedback resistor (other end of the wire going to the + terminal of the main speaker jack) or just disconnect the wire altogether if the speaker/amp combination sounds good for you.