That "FET Drag"

[nicosci]

Ok so the 2RJM has a dummy "FET load" drag resistor (220K) across the last PS Cap's + to Ground to simulate a FET load on the B+ on that V1 node. This is shown in Taylor's layout and as well as Ryan @ToneGeek and it certainly IMO has an impact of the amp's response in the preamp. I wanna change mine to match it.

1. So I am pretty much about to do the mods but I am here asking cause I'm OC and I always wanna be 100% sure before I do anything. Since the Ceriatone version has a "Precision" PS cap array (8x 47uF), I wanna ask if this mod can be done safely (Photo Below) as it would be if the cap array was like in the normal Wonderland config (4x20uF). ?

Like in pic;

tag q1.png

Will report back after mods. Thanks! Cheers!

[martin manning]

Yes, looks good. Take some before and after voltage readings on the supply nodes and on the preamp plate to see what you got.

[nicosci]

Yes, looks good. Take some before and after voltage readings on the supply nodes and on the preamp plate to see what you got.

omg thank you for replying!

Yes! I actually have a few things I wanna do to the Ceriatone including correcting the "higher" preamp voltages as compared to 2RJM. I will definitely measure all voltages as I can cause I am aware they'd all change as I plan to change the 1st dropping to 2k2. I will also reconfigure my v1 node to supply only v1.

Also worth noting my 6L6 supply is lower at 426-433v as opposed tp 445v, in contrast my preamp plates are higher than recommended as in TR. This is the reason Im re configuring that 1st dropping stage.

Anyway I attached an AN layout with my current voltages (Written larger beside AN voltages) :

Nick Cer Volts added ANW100w jan2017.png

Cheers!
Nick

[nicosci]

Also would a 2 watt CF resistor be adequate there?

I suppose yes but then I think about it and I'm not sure anymore lol/

[martin manning]

2W should be plenty, even for the worst case with no tubes installed. It will never see the full plate voltage, but if it did the power would only be V^2/R = 450^2/220k = 0.92W.

[nicosci]

2W should be plenty, even for the worst case with no tubes installed. It will never see the full plate voltage, but if it did the power would only be V^2/R = 450^2/220k = 0.92W.

What a relief. Thanks for the computation! Feels great that even in that situation it's well within half of it's rating.

I have these nice little 2 watt Taiwan CFs with thick leads and good size overall that I wanna use, cause my run off the mill 220k 3 watters look like they'd crap out first than anything

IMG_20220130_025749.jpg

[rccolgan]

This is cool! Looking forward to the results.

Fwiw I don't think I was ever able to get 445v on the plates without a super cold bias or different PT (Ceriatone 345-0-345). Any of the fender twin reverb 320-0-320 would get me in the same range you are measuring

[nicosci]

This is cool! Looking forward to the results.

Fwiw I don't think I was ever able to get 445v on the plates without a super cold bias or different PT (Ceriatone 345-0-345). Any of the fender twin reverb 320-0-320 would get me in the same range you are measuring

That's good to know Yea I actually thought maybe its better I leave it. Btw are the voltages consistent among the JMs you've poked around with so far?

[rccolgan]

This is cool! Looking forward to the results.

Fwiw I don't think I was ever able to get 445v on the plates without a super cold bias or different PT (Ceriatone 345-0-345). Any of the fender twin reverb 320-0-320 would get me in the same range you are measuring

That's good to know Yea I actually thought maybe its better I leave it. Btw are the voltages consistent among the JMs you've poked around with so far?

Yea this will be a Ceriatone to TR convert indeed thanks to you sir, imma just clear my bench and get to it hehe.

430v B+ (measured to ground reference) on the real JM Sig. I didn't measure the bias at the time to know how hot or cold it was running. Stock tubes and stock bias from Two-Rock.

[nicosci]

Thanks Ryan.

Ok so it's done.

Heres a photo of my new voltages.

IMG_20220201_021838.jpg

Figuring out how to best host the two clips of before and after. Anyway the change is significant. Its less Fender bright and more dark indeed. Also definitely you feel the drag on v1. Still need to play loud in daytime.

Cheers all!

[nicosci]

Take note I've only done the 220k, the wet dry mixer, and the 1st dropping stage. This is the effect on clip below.

Used a phone to record at 1 Master btw ..so can't really hear the rather ice picky nature of the before. Also since I moved the master and gain in between clips, I can't compare volumes based on the clip. I should play it more tomorrow.

[rccolgan]

Take note I've only done the 220k, the wet dry mixer, and the 1st dropping stage. This is the effect on clip below.

Used a phone to record at 1 Master btw ..so can't really hear the rather ice picky nature of the before. Also since I moved the master and gain in between clips, I can't compare volumes based on the clip. I should play it more tomorrow.

Great playing and great demo of the changes! That's a bigger of a change than I would have expected! You're right that the top end chime is less. I wonder if putting a 5751 tube in v1 without the 220k gives you a similar voltage drag

Do you prefer before or after the 220k change?

[nicosci]

Oh thanks Yea definitely a different amp altogether! Finally all those YT clips of the limited 25 make sense to me now. The Ceriatone wasn't like that. There's something you feel in the clean. I feel the Trad Clean has more of that thing. Re 5751, hmm interesting thought. Definitely I prefer the mods. Much similar to the sig. Actually I now hear what 100w does different, when I compared my clip side to side with your fairfield clip, actually that's why I did that similar riff you did at the end of gravity, to compare them!

Even the lows now are huge. Not sure how much of it was the mixer. It thumps now. I think my cheapo phone cant capture those frequencies. Oh and btw I took the voltages too frequently at every step along with the wall voltage. Now I see a direct correlation of high line voltage to a stiffer feel, and lower= sag!

Cheers! Thanks I couldn't have done this w/o you man.

[martin manning]

Definitely I prefer the mods....

Just to be clear, you prefer the amp with the FET simulator resistor and the lower V1 voltages?

[nicosci]

Definitely I prefer the mods....

Just to be clear, you prefer the amp with the FET simulator resistor and the lower V1 voltages?

Yes. It's like the amp is as it was originally conceived. Louder and dynamic as well