It’s a great amp with wonderful tone and plenty of power. Always works and sounds great. Had the tubes replaced with American ones a few years ago which made it even better. Always loved the Fender “Bell Tone” and this one has never let me down. Previously had a Pre-CBS deluxe and a twin. I’ll put this up against both of those any day.

Installing a bias pot: use a 10k linear pot and mount it through the bottom of the chassis, below and toward the pilot-light side of the tremolo pots. Remove R59 and solder two lengths of wire to the PCB where the resistor was. Connect one of those wires to both the middle and one end tab of the pot. Then solder a resistor to the remaining tab and connect the other end of that resistor to the second wire. For values, start with a 10k resistor. What you’ve now done is replaced the fixed 18k bias set resistor with a 10k resistor in series with a 10k pot, giving you a range of roughly 10k–20k instead of a fixed 18k. Reassemble the amp and check your idle current — you’ll want to see about 30–40mA per tube. If you can’t get the idle current high enough (which often happens with NOS American tubes or Tesla 6L6GCs), replace the 10k resistor you added with a 5k. The 10k works fine for Svetlana tubes, while Philips 6L6WGBs may need the 5k, and the Tesla 6L6GCs definitely will. From my experience: Svetlanas have a nice midrange and are great all-around tubes. Philips tubes are clean and bold at low volume and break up beautifully — a solid blues option. Teslas remind me of 7581As — big, full, clean, and loud, with tons of headroom. They’re also extremely durable and can be pushed hard. My personal pick for this amp is the Svetlana, which I bias at 36mA per tube. With an adjustable bias, you’ve got real flexibility. A neat safety trick: carve the tip of a wooden skewer into a flat slot to use as a makeshift screwdriver when adjusting the pot — it eliminates the risk of electrocution. Please, folks, be careful!

How did you install the bias pot? Did you just replace R59 or 58, or did you add a pot and replace one of the resistors. I’ve been looking for some instruction to do that but haven’t found any.

I put in 2 Weber 10A125,s and NOS tubes. Put in a bias pot and now it,s a tone monster! Takes pedals well. Plenty loud enough, too.

I managed to find one of these new back in 1991 with the 2 X 10 Oxfords. Great little combo and very reliable. The only mod I made was to swap out the Oxfords for Jensens, made a huge difference in brighter tone. 35 watts may be an understatement in my opinion, this baby is Loud !