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previous: Craig I've been trying the same type of e... -- 1/20/1998 5:24 PM

Re: Unused Triode as Gain Stage

1/22/1998 7:29 AM
Mike T	Re: Unused Triode as Gain Stage I used it last night at rehearsal, and it worked real well. The distortion is soft and smooth and it cleans up pretty nice. The volume is adequate for rehearsal. I have a gig tomorrow and I plan to use it in parallel with my Fender Pro Jr. The current configuration is: (2) NOS JAN nude bottom 6V6s (Phillips I think..I've been using these tubes in and out of different amps for awhile, so I think a new set would give me more headroom..the sockets will also accept EL34s and I tried a set of Sovtek EL34s in there, also tried 6L6STRs, 6L6WGBs and Sovtek 5881s, but liked the 6V6s for their soft breakup and adequate headroom), 12AX7 preamp and 12AX7 cathodyne PI, (6) 1N007s for rectifier, Hoffman PP 30 watt OT (with a 4 ohm tap), Celestion 35 watt 4 ohm 8" speaker (Weber VST has an 8" that I would like to try, but it wasn't available when I bought this one), 500 ohm rK. Around 410 plate volts drawing 31mA per tube. I tried 5751, 12AT7 and 12AU7 for preamp and driver, and I found the same effect could be achieved by backing off on the guitar volume, but with the 12AX, the additional drive is available. The circuitry is essentially a Princeton 6G2 with cathode bias, SS rectifier (so I only had to punch 1 hole in the chassis), and no vibrato. I may try the long tailed driver eventually, but for one thing it is very tight on the circuit board now. How did you get all the stuff for a Deluxe tone stack and long tailed driver on that little board? The PT is the original SF Champ and it still heats up, but not nearly as much as when I was using a 250 ohm rK. ButI have an AC fan I got from Mouser (its for mounting internally on a chassis, but I just put it on the bottom of the cabinet propped up to the right angle with a little block of wood) that keeps the PT and tubes as cool as if they were off. I have been toying with the thought of cutting the baffle and installing a 10" spkr, but I'm gonna leave it for now. It really has adequate volume for rehearsal and I'll find out how well it works on a gig tomorrow. I tried to install a varialbe negative feedback pot, but couldn't get it to work. There was an article in GP a few years ago and the guy called it the 'Soul Control'. I've put it in a few other amps with no problem, and it worked well and was very effective. I tried setting the -feedback up like on the schematic, off the 1500 ohm rK of the second gain stage which goes to ground and to a 47 (or 470, I can't remember now) ohm resister directly to the speaker jack. I put a 5k ohm pot in line there to no avail. I had a 1mf bypass cap there but removed it for this mod. Now, since I couldn't get the -feedback pot to work, I put in a .68 cap, which adds a good amout of gain to the circuit....maybe too much. That's pretty much it and for now I'm fairly content with the results.. Mike

1/22/1998 7:29 AM

Mike T

Re: Unused Triode as Gain Stage

I used it last night at rehearsal, and it worked real well. The distortion is soft and smooth and it cleans up pretty nice. The volume is adequate for rehearsal. I have a gig tomorrow and I plan to use it in parallel with my Fender Pro Jr. The current configuration is: (2) NOS JAN nude bottom 6V6s (Phillips I think..I've been using these tubes in and out of different amps for awhile, so I think a new set would give me more headroom..the sockets will also accept EL34s and I tried a set of Sovtek EL34s in there, also tried 6L6STRs, 6L6WGBs and Sovtek 5881s, but liked the 6V6s for their soft breakup and adequate headroom), 12AX7 preamp and 12AX7 cathodyne PI, (6) 1N007s for rectifier, Hoffman PP 30 watt OT (with a 4 ohm tap), Celestion 35 watt 4 ohm 8" speaker (Weber VST has an 8" that I would like to try, but it wasn't available when I bought this one), 500 ohm rK. Around 410 plate volts drawing 31mA per tube. I tried 5751, 12AT7 and 12AU7 for preamp and driver, and I found the same effect could be achieved by backing off on the guitar volume, but with the 12AX, the additional drive is available. The circuitry is essentially a Princeton 6G2 with cathode bias, SS rectifier (so I only had to punch 1 hole in the chassis), and no vibrato. I may try the long tailed driver eventually, but for one thing it is very tight on the circuit board now. How did you get all the stuff for a Deluxe tone stack and long tailed driver on that little board?

The PT is the original SF Champ and it still heats up, but not nearly as much as when I was using a 250 ohm rK. ButI have an AC fan I got from Mouser (its for mounting internally on a chassis, but I just put it on the bottom of the cabinet propped up to the right angle with a little block of wood) that keeps the PT and tubes as cool as if they were off.

I have been toying with the thought of cutting the baffle and installing a 10" spkr, but I'm gonna leave it for now. It really has adequate volume for rehearsal and I'll find out how well it works on a gig tomorrow.

I tried to install a varialbe negative feedback pot, but couldn't get it to work. There was an article in GP a few years ago and the guy called it the 'Soul Control'. I've put it in a few other amps with no problem, and it worked well and was very effective. I tried setting the -feedback up like on the schematic, off the 1500 ohm rK of the second gain stage which goes to ground and to a 47 (or 470, I can't remember now) ohm resister directly to the speaker jack. I put a 5k ohm pot in line there to no avail. I had a 1mf bypass cap there but removed it for this mod. Now, since I couldn't get the -feedback pot to work, I put in a .68 cap, which adds a good amout of gain to the circuit....maybe too much.

That's pretty much it and for now I'm fairly content with the results..

Mike