Recent content by Joost Overmars

Appears to be in very good condition with still the original +5/-5 EQ knob which I’m missing. Have fun with your SB!

Yes you can but....since the current output tubes are non-original it’s very likely that the person who put them in has also changed the original bias circuit to match the Russian tubes. In that case the bias voltage will surely be wrong for the 6L6’s. I would stick to the Russian tubes till you...

Yes you should bias the new 6L6’s. If you don’t know how to do it yourselves, don’t. Lots of lethal voltages inside. What you CAN do is adjusting the output tubes matching pot on the backside for minimum hum.

No difference, just different ways of measuring power.

Interesting! The pentode part of the 6CX8 is used in the Super Twin Reverb as reverb tank driver and the tri-triode 6C10 is used as reverb recovery, distortion circuit and reverb/dry signal mixer. The Studio bass has reverb nor distortion channel..... very strange indeed. My best guess is that...

Are you sure you have a Studio Bass chassis in the combo? Because this is the tube diagram of a Super Twin! Please send a photo of the front panel.

Yes, sorry, you're right, 4 ohms is the spare lead.

When you have the head, look at wires that come out of the OT: on the primary side there are 5 wires that go to the output tubes. On the secondary side are 2 wires (older models) OR 3 wires (later models). At some point they started to use the same OT on the super twin and the studio bass. That...

Fender started to use them late ‘70’s when they started with the ultralineair power stages on the solid state rectifier diodes and than also on the preamp stages to prohibit HF oscillations. Fender 75, super twin (reverb) and studio bass have them as well as more later fender amps. They do...

Yes exactly! I left the snubber cap on the 2nd V1b stage in place.

Yes, I just changed the tonestack. I left the 750µF kathode bypass cap and removed the anode to ground snubber cap. I liked the change even with all 3 tone controls at 5. The 5 band active EQ works as usual.

Finished head & cab. Recap & retube. Power stage rebuilt with larger screen resistors, new grid stoppers & 1R bias kathode resistors, variable bias, first pre amp stage revoiced as silver face bassman (500pF treble cap, 100K slope resistor), snubber cap removed. Great, open sound now! Very loud...

In the middle of splitting the combo...

Thanks! The 7581A’s are pretty expensive here in the Netherlands. I’ll stick to the Tungsol 6L6, like them more than JJ’s.

I have both: a 1974 Bassman 10 and since this week a very worn 1978 SB (for a very small prize), that I’m reviving. The difference in output and tone is huge. The bassman 10 puts out no more than 40 watts because of the very small OT. The original 10” speakers are not very efficient. I...