5F2a-ish with Tremolo

I have a bunch of 7-pin triodes and pentodes. Time to do weird things to them.



I probably should stick a 2.2M resistor between the wiper and ground of the master volume pot to maintain a ground reference for the grid of the power tube in case of wiper failure. The alternative is to hook up lug 3 of the pot to the power tube, and the wiper to the coupling cap, but that would present a variable load to the pentode, which may not be a bad thing for what I'm trying to accomplish here.

I got the idea for the optocoupler from a thread from el34world (https://el34world.com/Forum/index.php?topic=24334.0) The tremolo tube will always be on, so there's a separate power node to isolate it from the rest of the circuit.

Chassis (10" x 6") drilled and painted.

 

Yep, just to mess around with the operating points of the tubes. Switch C attenuates lower frequencies when open to tighten up the tone on overdrive.

 

Now, ain't that the cutest little power supply you'd ever seen!

 

All done and wrapped up.



The optocoupler tremolo sounded great, but I had no depth adjustment. With the recommended 1M pot, I went from swampy to nothing within a tiny fraction of the turn of the pot. I tried a bunch of pots, down to 25K. With the 25K pot, I had about 1/3 of the turn available. However, because it's in parallel with the gain pot, there was basically no load on the triode, so the gain was down in the dumps. I didn't have another VT5C1 to swap in, so I converted to an output tube bias shifting tremolo, with an obligate cold bias. A 6V6 dissipates just a hair under 8W, and a 6JC5, just a bit over 10W.

My God! It's full of switches.



I did the set up with a 6ER5 and a 6AU6 tube.



The initial impression with the 6ER5 and the 6AU6 is that I can dial in a pretty good sounding amp, and I suspect I will be able to do so with the remaining tubes.

The 6H*5 triodes are pretty much the same. The 6ER5 and the 6ES5 are also pretty close. So it looks like I'll have three different triodes. With the 12 pentodes, there are 36 different combinations of triodes and pentodes. Given each triode have 3 different plate loads, and each pentode have 9 different combinations of screen and plate loads, there are 972 settings to try out. Adding in the triode switch on the pentode, there is a further 324 possibilities, so a grand total of 1296 combos. This is silly.

 

The 6BD6 tubes were leftovers from my Gibson GA-100 build. They were driver tubes for the 6L6's. They have a clean, compressed sound with a slight breakup with the gain turned up. Excellent choice for pedals, especially my home brewed big muff pi.

 

That's not a lineman's splice. I'm not that skilled. It's 24 ga copper wire wound on an appropriately sized mandrel serving as a coupler.