Dual-ganged pot value for PPIMV

[pjd3]

Hey there all,

Is it correct to make the dual pot value for a PPIMV the same as the power tube grid leak resistors? Without being 100% certain it appears that it would.

So, in a Marshall plexi the grid leak resistors for the power tubes always seem to be 220K but, in Sluckeys 6V6 plexi schematic the grid leak resistors are 100K ohms.

Just use a dual ganged 100K pot for the ppimv volume pot?

Thank you,
PJD3

[Colossal]

It depends on the amp and the tubes used, as well as your desired tonal goals and performance for the control. Although Fender routinely used 220k/220k grid leaks in virtually every 6V6 and 6L6 based fixed bias amp, if you look at and follow the 6V6 datasheet, the max grid leak value for fixed bias is 100k, not 220k. Mark Huss designed the original 6V6 Plexi and used 100k for the grid leaks. This amp had very high plate voltage with much lower screens and ran in fixed bias. I built one about 12 years ago and it was a smokin' amp.

[pjd3]

Thanks for responding Colossal,
The 6V6 plexi I'm in the process of building is Sluckeys 6V6 plexi which I believe is based upon Mark Huss's 6V6 plexi.
This amp does have 100K ohm grid leak resistors on the power tubes. I choose to build this in an attempt to have a more civil stage volume and still get a degree of crunch and grind in the tone. As of now, I'm not versed in what the tonal differences would be between having 100K vs 220K grid leak resistors but, if 6V6 are good with 100K grid leak resistors and it leads to a smokin" amp, then I'm totally game for it! Sounds like a good start. I guess I can assume that using a 100K ohm dual gange potentiometer for the PPIMV control is the thing to do?

Thanks man,
PJD3

[Colossal]

Yes, use a 100kA-dual gang. Get a good one with well matched sides. The amp will be plenty loud. I ran mine with a closed back 2x12 with Greenbacks and it was very chewy and wheezy and fat. I used a Vibroverb power transformer and a Marshall 20W output transformer wound to 7k6 on the primary. I would stick to 47uF - 5k/choke - 47uF - 22uF - 22uF in the power supply. To rebuild it today, I would likely go with a 32uF/32uF cap can or individual caps for the OT and screens. I tried going higher than 47uF on the mains and it was too fast and hard for my tastes.

Have fun with your build.

[pjd3]

I'll look for a very high quality and matched dual pot. Someone mentioned a Canadian company that made some unusually well made pots, costs a bit more but, thats fine and expected.

Sluckey told me to use just a good old Deluxe reverb type choke (mojotone 5H/160 ohms 75mA)
I already installed a Classic Tone PT 330-0-330 and made sure it handles all the heater currents so should be good to go there with good voltages, current and power handling. It also has F & T 32/32uF cap cans.

I'm going to try the OT that was in the Bogner Alchemist chassis (the one I'm re-using for this project). It was for 2 6L6's but I'm going to try either an 8 ohm speaker on the 4 ohm tap or, a 16 ohm speaker on the full 8 ohm tap to reflect a more appropriate impedance for the 6V6's. If for some reason something sounds off, I'll just spring for an OT with a 6k - 8k primary. Enough people have led me to believe it is worth a try!

Thanks so much Colossal, I'll be moving on with those steps. The board is all done and most of the sockets and pots are all wired up. A little ways to go till amp d-day.

Best,
Phil PJD3

[Colossal]

You're off to a good start. You'll be fine with that ClassicTone PT. FWIW, I used a 10H 280ohm Marshall choke in series with 5k 5W for the screens. Had some nice compression.

The Canadian company is PEC, Precision Electronics Corp and those are very good. Pricey, but worth it in my experience. They often measure very close to the stated value and with well matched sides.