I've recently build a JCM800 6V6 (RobRob): https://www.tdpri.com/threads/jcm800-6v6-variant.1027817/ The amp is quite bright (at the lower volumes I tried). I've been analyzing the preamp signal: https://www.tdpri.com/threads/signal-tracing-through-a-jcm800-6v6.1040391/ In the last signal tracing thread one can see that I found two strange effect in my preamp (and I haven't found a reason why other jcm800's shouldn't have it). A) With the gain around 3 a 'sharp bends' occurred. It was found to be draining of the larger capacitors in the tone stack through the cathode resistor. The cathode follower was unable to sink the current. B) Once that problem was solved, it became clear that another strange signal showed up at high gain settings. It was found to be caused by the pre-warm-biased-stage treble bleeder. Some robrob tweaks will be reverted. The 330k in series with the gain pot will be replace with stock 470k as I don't need the gain. The 470pF treble bleed will be replaced with the 1000pF as this will actually let more mids through instead of shrill highs. This comparison will be with the stock jcm800 preamp as a starting point. My solution seems to be a win-win-win situation and shares quite a bit with the advice of @LetItGrowTone. 1) Remove the 470pF treble bleed 2) Lower the cathode follower cathode resistor to 47k (Merlin's favorite) 3) Increase the slope resistor of the tone stack to 56k 4) Lower the smaller tone stack capacitor to 250pF 1) will get rid of B), but quite a lot of highs will be lost. 2) and 3) will get rid of A) and will drop some bass/mid. 4) is to conform to the 56k standard TMB tone stack. The overall drop in preamp signal can be made up by a different MV setting. Here is the comparison in the time domain (stock: green, new: blue): MV 10%: MV 100% Capacitor draining A) is solved and so is B), although it was hidden by A). And in the frequency domain: Quite some highs are lost, but this is somewhat evened out by a bass/mid loss. Overall the amp will be less bright, but this is still adjustable by the tone stack pots. Of course, actually trying and listening will give the final verdict. I don't have a stock of resistors and capacitors, so this theoretical exercise is to find out which ones I absolutely need to order along a bunch of others to justify the shipping cost. Any comments?