Guitar Gear Forum

Just try it out, what I've described. This is a matter of cross talking (hope this is the right word, I'm not a native speaker), which depends on the real location of the traces and wires in the amp, which you don't see in a schematic.

FWIW, käsebrot is correct about the bleed over (or whatever you want to call it) between the two channels on the 22.

i was checking the amp now. on the 50 there continuity through the relay at all times on the 50 for the clean channel. on the 22 that is not the cause. you guys might wanna recheck whatever it is you checked to come to your conclusion cause im
using a tester right now. and the crunch channel does not feed through to the overdrive channel. the relay is for sure wired different on the 22 than the 50 that is plain to see. and the crunch channel does not feed through the relay on the 22 while the overdrive channel is on.

i mean no offense but it for sure doesnt work like that on the 22. i even checked the traces for continuity. with amp off overdrive is on and crunch is off.
on the 50 when amp is off, overdrive is on, and crunch is on.

what is FWIW?

FWIW = For What It's Worth...

And I have nothing to go by other than my ears. One does indeed affect the other whether your meter reads that or not. It is easy to test. Anyone else with a 22 care to verify? I am heading out to the NAS Oceans Air Show so I can't record any clips but I can assure you that there is a bleeding over of some kind going on there.

oh cool im in the navy by the way.

i would check and listen but i cant at the moment. as my transformer is out on my 22

the only way it could be effecting it is the gain knob on the crunch allowing some signal to ground but from the schem, the way the gain pot is wired it doesnt apear to work that way.

käsebrot wrote:-The mods make the amp even better - but won't change the overall basic sound!

You sure bout that? 10 resistors and a few caps could make a completly different amp on paper. Wouldnt even need to cut any traces. Transformers are decent size. Caps could be upgraded. Brown eye mod (even though theres a lot involved) sounds nothing like a 20h. Im positive this amp has the (or one of the best) tweekers posabilitys in any amp.

My vintage tubes sound superb in my Ac15 and 18watt including the Holland rx4 el84s I just got. Im pretty sure the PI values dont really fit the el84s and need addressing. Mike seemed to just take the basic schematic and and throw el84s in there. I believe Mike called the Atomic 16 a "firebreather"

agreed, drainbamage.

Im getting some better tones out of it now.

I swapped in a 12ay7 in V1. Helped smooth out the gain and the amp is more articulite. I have to turn the gain up more to get the same level of gain however it is smoother sounding.

I swapped in JJ el84s. My multimeter is needing batteries.. so I stuck them in anyways. There are most definatly on the hot side. The plate didnt red plate but ill have to be carfull untill I get it biased. This helped with some of the fizz I was experincing.

I am running 60 ft of coily cables to the amp. This helps soften the top end a touch. Putting my blackstar Ht boost pedal in the front end allso colors the tone in a good way when off. This amp just loves this boost to be enngaged. Im a crunch guy and I still cant get good crunch out of it. Right now it can do some good gain tones though.

Im using a les paul double cut with treble P-90 through a sealed oversized 1x12 with a greenback. The jca20 also loves my rockcrusher . These are my amp settings-
Gain 6.5
Bass 1
Middle 6
Treble 5
Master all the way
Presence 0

i

Drainbamage:

Only changing the plate resistor on V1 to 100k, the cathode to 1,8k, swap out the 3rd bypass 1u doesn't make a whole other amp. Yes, I'm sure about that. You were not talking about "10 resistors". For sure, you can swap half the parts out and build a complete new amp. But I don't see the sense behind that, in this case, you could also buy a amp, which is more to your taste already in stock condition.

The JCAs are basically Soldano Hot Rod + amps, which are only hot rodded Marshalls. You can go back, if you want less gain and more bite, just compare the schematics of Soldano and Marshall, then you can figure it out. But then there are different voltages, different transformers...

My way is, to take these amps and improve the sound, make it better by doing as much changes as were necessary but also as few as possible. I have heard so many JCAs, which were modded and modded and finally sound like crap. My recommendation is to do a few changes where they make sense and for the rest just replace the stock caps and tubes with good ones. This helps a lot and the amp will sound really good!

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Shep - do you have pics of what you did? Curious to see the final layout and what you mean about removing heater wires from rest of secondaries.

Good to see the latest burst of activity!

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GRIMESPACE wrote:Good to see the latest burst of activity!

I read this entire thread! Ive been reading the HC one too but its so hard with all the pictures broken

Shep I cant listen as my computers sound driver is messed up but I really want to! What do you mean by elevating the heaters? The wires off the chassis? Im interested in how it sounds after but the heater wires on the pcb arnt twisted so im kinda on the fence in how much it helps. Then again Im not really up to date with Pcb construction.

Are the green boards better than the cream JCAs? Does the Green over the tracings have a possitive effect on unwanted noies ect?

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Oh I see what you did I missed those pictuers before I posted. That board had the heater wiring traced into the board right?

yes, you have to cut the traces around the sockets. on the underside of the board

Gotcha you cut the heater traces off and twisted some new wire in. Cool. I play with P-90s mostly now so its all ready kinda noisy so it might not be worth it for me. However I did see one guy clean up all the wires by shortinging them. Something to think about. Im all so trying to be unintrusive to the board.

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käsebrot wrote:Drainbamage:

Only changing the plate resistor on V1 to 100k, the cathode to 1,8k, swap out the 3rd bypass 1u doesn't make a whole other amp. Yes, I'm sure about that. You were not talking about "10 resistors". For sure, you can swap half the parts out and build a complete new amp. But I don't see the sense behind that, in this case, you could also buy a amp, which is more to your taste already in stock condition.

Well my original idea was 5 resistors or so and a cap. 10 resistors I could change the bias on all triodes and then some. The 5 was a starting point and I hope to do as little as possable. I have 3 other amps right now and this one was bought to tinker.

I play the treble p90 pup on my les paul double cutaway so id like to voice the amp around that. I like how well treble pups cuts through. It is a hair to bright so cliping the 3rd gain cap will acheive two things. Reduce the gain and thicking the tone. If its still too bright clip c23 bright cap or maybe try it up to a .0022 cap.

Two free mods im going to start with is clipping the 3rd gain stage cahode cap and move the negitive feef back to the 8 ohm tap.

C23 on 22H is one of the two PI coupling caps.

If you mean C23 on 100HDM, this makes pass treble over the 2,2M resistor in the crunch channel. The higher the value of the cap, the more gain you get. I like 270p better there. You could also lower the 2,2M to 1M and bypass it with 470p, then you get the configuration of the 22H.


And yes, uncovered traces produce less hum, that's why the 22H has no covered traces. So I was told by Jet City, they checked that out.

C23 on the 20h is a 470p bright boost cap (from the Diy schematic floating around)

I thought the old version JCAs had cream boards then switched to the green. Incorrect?