Modded Tremolux

[johnnyreece]

Ah but your single triode Jet trem might’ve been the best answer.

Maybe. But the Tremolux paraphase inverter might not get along with the J12 trem. I don't know. Looks like the trem would also couple through that 6800Ω to the lower PI grid. I have no idea what might happen with that. Could be a new discovery. Could also be a heartbreaker!

Yeah, I think I'm smacking enough changes on the poor Tremolux that maybe I'll try this particular idea another day. I really do appreciate the discussion, though!

[johnnyreece]

So, I've played around with the tremolo section to try to get more range. I wish I could find an oscillator calculator or formula that *doesn't* require all three resistors and capacitors to be the same value so that I could experiment with this...Anyhow, does this seem like it might work? Might be another "slap it together and see how it sounds" type-thing.
Any input is appreciated!

Tremle Dee Tremolo Mod.jpg

[johnnyreece]

So, I had a little time this weekend and found some errors on my schematic and layout. Got those sorted out, and these are my "As-intended-to-be-built" schematic and layout. Feel free to share any thoughts you have on why it might or might not work, or if you think something could be better!

[LOUDthud]

A word of warning on this amp. With that switch changing the bias on the output stage, B+ is going to be moving around. Because of the way that the Tremolo "Depth" control is tied into the Phase Inverter, if B+ is too high, no signal will get through the Phase Inverter to the Power Tubes. Solution, lower that tail resistor in the Phase inverter.

[johnnyreece]

Thanks for the heads-up! Do you think something like 4k7 would be better?

[Colossal]

What is your goal for the bias switch?

[johnnyreece]

Just being able to switch between hot, mild, and cold bias. Still deciding what values. May go with 2x500 and a 1k. That would give me 250, 333, or 500. Just something to play with. It would also give options if using different output tubes (thinking about maybe using 6K6 at times, or if I beef up transformers, 6L6). I wouldn't be switching on the fly, or anything like that.

[LOUDthud]

Thanks for the heads-up! Do you think something like 4k7 would be better?

You are going to have to experiment to get it working with all combinations of output bias. A higher resistance Depth control might be needed. The Depth control pulls the cathodes positive and that starts to bias the PI colder reducing the gain. This is a unique circuit among Fender amps.

[johnnyreece]

So, I discovered a couple things. One, I had my layout backwards (d'oh!). Got that mostly updated and will repost. There were a couple minor changes made, but I think overall, the design is about the same. I finally got off my butt and figured out how to program my CNC to drill my turret board, so that's cool. I plan to eventually type up a tutorial (because I had a lot of trial and error to get it figured out). I went from DIYLC (for design) to Inkscape (to convert to gcode) to Candle (to send to the CNC). All free software. None of it was particularly hard to do, but getting the sequence right took some doing for my thick skull. I think it turned out okay, though.

[johnnyreece]

I know it's been a long time since I've posted on this, and there's not much to update, but here goes: My original PT turned out to be toast after preliminary testing. So, I bought a new one with multiple secondary taps from Weber (it was cheap!). With that in mind, I'm incorporating a high/low B+ standby switch. Unfortunately, the PT was not a stand-up type, but had wires coming out of each endbell, and they didn't' make a conversion kit for those, so I made my own feet and drilled the endbells. Looks okay in my book. I've also got the board made up. I've been working on my CNC software, and I think I'm ready to experiment with faceplates soon. The plan is to paint the back of a piece of plexi gold, carve the graphics, then fill with black; kinda like a Marshall. Oh, and most importantly (hah), I decided on a name: Tremolead.

One thing I've been wondering about...with the addition of this PT, I'll be able to use higher power tubes, including EL34, KT66, etc. I'm wondering if I should maybe add screen resistors? If so, is there a good compromise value I should use? I truly appreciate any input!

[Stevem]

Swapping around to different b+ voltages calls for more then just adding screen resistors which should be done anyway.
You need.
A higher wattage rating Ot.

You need switchable cathode resistors.

The use of a EL34 requires pin 1 to be tied to pin 8, and many times since pin 1 is not used in a 6v6 or 6L6 type tube that pin is used as a 1 pin terminal strip/ tie point.

[johnnyreece]

Thanks for chiming in. I'm using a JTM45 OT, so I'm covered there. I'm also using switchable cathode resistors (set up to change between 250, 333, and 500). I'll also make sure to tie 1 & 8 together if I end up going this route. The question still stands about the screen resistors, though. I'm thinking a minimum 1k? I don't really use EL34 much (and really never in Fender-type designs), so I'm hoping to get some input from those of you with more experience on the Brit side of things.

[johnnyreece]

I've got a schematic draft drawn up (please note, it's only had a cursory review - will check later for accuracy). I'd appreciate if anyone wanted to put a pair of eyes on it. The schematic doesn't make note of the voltages, but the PT has dual secondaries (330-0-330 and 360-0-360). As of now, the schematic doesn't include screen resistors, but that will quite possibly change at some point. Anyhow, thanks everyone who's still following along with this! I've got the board assembled, and am hoping to get moving a little faster soon, but my wife is opening a candy store, so that's taking a lot of my *fart around with electronics* time.