Thanks for all of your thoughts. The amp has replacement Tolex and speaker. I fabbed up a bracket and it would have worked fine, but somehow it looked less 'correct' than a proper fender-style pot. With a bias probe, I reckon I could do the bias adjustment without removing the chassis. Or at the very least, just take it out and flip it over. So I drilled the hole... Some pics below for interested folks: After all of your advice to keep the circuit stock, I went with F&T caps - the closest values were 10 and 22uF. Hopefully not too far out of spec. Cathode bypass filter caps replaced with Sprague Atom 25uF50V. I found another change to the circuit - the .0033uF cap in parallel to the plate resistor on ch1 has been removed. I don't have one to hand so I'll have to try it out to decide if I need to put it back in. Everything else is back to stock according to the schematic. I used carbon comp resistors throughout. They all measured within spec, but they might be a bit noisier than modern ones. Bias cap is replaced - Sprague Atom at 100uF100v. I've put a 15K resistor in series which gives the range 15 - 25K, but that may end up being too low. Bias pot installed. I wonder here the if resistor could be grounded to the back of the pot as in later circuits? Next job is biasing... Bias pot from the underside of the chassis. 3-prong power cord installed. I used Doug's instructions for that. Time to do the start-up routine, I made a lightbulb limiter for my 5F6A build according to RobRob's instructions. I'll go through the same process for this.