Guitar Gear Forum

Can somebody please reference the picture below and tell me which tube is which? Specifically the preamp tubes. I've read that replacing PI with a 12AU7 makes a nice difference and I have one of those tubes but I have no idea which preamp tube is Pl.

I can't see the input jack, but I'm guessing it's the one on the right in that photo - V1 is usually the one closest to the input jack. (one closest to power tubes is likely the Phase Inverter, or V3)

One of the JCA experts or GAB amp builders/modders may be by shortly with a definitive answer, but in 95% of amps, V1 is the preamp tube closest to the input jack, and the PI the one closest to the power tubes, for reasons of simple topography. I would be shocked if the preamp tube right behind the two EL84 sockets was not the phase inverter.

I just Googled the circuit board layout and found photos that do indeed agree with what you guys are saying. V3 which is also PI is the one that's between the el38s. And the one right behind the input jack is V1. Thanks for the info, looking forward to switching some tubes out, powering it up and hearing what it sounds like.

Ta-dah! New grill and knobs, JJ EL84s and an EH 12AU7 in PI and I put blue LEDs in but the installation sucks so I have to redo it. I thought it sounded good before but the tube swap really brought it to life. Volume near max, gain about 3 and my Strat with Fat 50s is wondrous. I really heart this amp. I'm glad they're so cheap on GC used because I might get another one. Or two.

That isn't a crappy paint job on the grill, just oddball outside lighting.

So I am definitely looking to do/get some mods done to my amp or sell it. I know lots of guys offer a clean channel mod and this guy needs it desperately. Overall the amp sounds killer but no true clean tone is driving me nuts. Also, just watched this vid:

[video]https://www.youtube.com/watch?v=bQKbZCR_WqE[/video]

Here are the component changes. How hard do you think this would be (From YouTube comments):
"Here ya go bro... All of the components below will replace the stock resistors and caps. For example, R36 - 470k means that you will replace the stock resistor in that location “R36” with a 470k resistor"

Depth Mod - You’ll need a 500k potentiometer and a .0047u capacitor for this mod. You’ll cut the FB wire and place this in line.
Choke – R52 - Hammond 156M
C2 - .047uf
C5-.0022uf AKA 2200pf
C6-1n AKA 1000pf
C7-220pf
R1 - 47k
R5 - 470k
R9-500k
R10-700k
R18 - 220k
R24 - 33k
R26 - 33k - More Bite
R32 - 10k - Tighter Overall Tone
R36 - 470k

I'm pretty sure I made a bunch of those changes as well. I ended up reverting a lot of those changes back to factory. Some of them just didn't sound good at all. I was too lazy and didn't keep track of anything I did, for the most part. I do know the depth mod is a huge must. Bias that thing too. I also snipped one leg of C6 and put it on a switch I added to the front of the amp. There's also a mod where you jump a resistor with a small cap - to get rid of some of the sizzle on the OD channel. Fuck if I can remember what I was doing 15 minutes ago. I changed the slope resistor (r26) but have no clue to what. I do know I did some stuff with r5 and r9, trying different values, and ended up settling back to factory. Again, some of the changes should sound good in theory but don't translate well audibly. Dunno. Your mileage and all that jazz.

Hey folks had a chance to open up the volume today on my 50H. Here are a cpl clips, phone recording so...

https://youtu.be/bdeFSlM5GW0

https://youtu.be/YmUQvT80fdE

Heya, Jimmy - sounds pretty cool. Extra style points for rockin' the pointy headstock 80's carvin

If you use the [video] [/video] tags around the youtube link, it'll show better... here's the embedded ones for ya

[video]https://youtu.be/bdeFSlM5GW0[/video]

[video]https://youtu.be/YmUQvT80fdE[/video]

Here's my JCA50H and my Carvin DC135 (and my SG, which has since been traded for a Boogie Mark III)

Cool I'll use that next time. Yeah I'm an old 80s rocker so I love those old Carvins. Thanks !

Sweet DC135, man!

I finally got my blue LEDs sorted out. This little amp kicks ass.

Hello!

This is my first post here.

I recently bought myself a JCA22H. It doesn't cost much and seems to have quite a good reputation as a platform for modding so I thought I'll give it a try.

The first thing I will do is to convert the crunch channel to a 2204 according to the info from stump. I'll also add a switch to bypass the first tube which will be the same as the lo input on a 2204. The switch is wired as a true bypass switch in pedals.



EDIT: The slope resistor (R26) will, of course, be changed to 33k even if it's not shown in the schematic above.

My JCA 100h is on the fritz AGAIN! I took it to my amp tech about 9 months ago for the same intermittent volume cutting problem. Why is this happening? I'm playing at band volume and suddenly in the middle of a song I disappear, then come back. What's going on in my amp? Plus my my power light went off years ago, but that's not really a problem for me.

I'm thinking about ditching the JCA and saving up for a used soldano avenger to replace it. And while that's clearly the preferable answer I don't have any money and that purchase would be a year or more off, and that's if anything catastrophic didn't happen first. I'd really rather not have to deal with that and just have a working JCA 100h which I was just fine with.

JerEvil wrote:So I am definitely looking to do/get some mods done to my amp or sell it. I know lots of guys offer a clean channel mod and this guy needs it desperately. Overall the amp sounds killer but no true clean tone is driving me nuts. Also, just watched this vid:

[video]https://www.youtube.com/watch?v=bQKbZCR_WqE[/video]

Here are the component changes. How hard do you think this would be (From YouTube comments):
"Here ya go bro... All of the components below will replace the stock resistors and caps. For example, R36 - 470k means that you will replace the stock resistor in that location “R36” with a 470k resistor"

Depth Mod - You’ll need a 500k potentiometer and a .0047u capacitor for this mod. You’ll cut the FB wire and place this in line.
Choke – R52 - Hammond 156M
C2 - .047uf
C5-.0022uf AKA 2200pf
C6-1n AKA 1000pf
C7-220pf
R1 - 47k
R5 - 470k
R9-500k
R10-700k
R18 - 220k
R24 - 33k
R26 - 33k - More Bite
R32 - 10k - Tighter Overall Tone
R36 - 470k

Ok, so this clip sounds fucking angry and awesome. Soooo. I am going back in. I already made a list and checked it twice. Shopping for components is easy as there is an awesome supplier local. Will see if I can score a used Tech 21, maybe. Mine right now is just a little looser and flubbier...This should tighten it up for sure. If I can get closer to THAT tone tho...Sheeeeiiiit...

beje, someone with more knowledge than I will hopefully be along soon enough to help you out. Also, don't forget tubes and bias. And always be careful poking around in there. Make sure you know what you are doing before sticking your hands near deadly voltages. And welcome to the forum.

beje, someone with more knowledge than I will hopefully be along soon enough to help you out.

I'm ok, I just thought I would share what I'm about to do. The 2204 mod is old news of course but maybe the hi/lo switch could be useful for someone. One thing though, in a JCA22H the first gain stage is used in both channels so these mods will mess up the overdrive channel. I have other plans for that channel so it's not a concern for me. I'll report back when I'm done.

And welcome to the forum

Thanks Meelocheck.

Hey Guys

I just registered here ..Was browsing this thread and I see that some of you are really into those Jet city's . Here are a couple pics of one of the few I did mod recently ..Don't be scared ! I know there is almost nothing original left :-)
This one is the same exact circuit as the CAE 3+ SE preamp's Channels 2 and 3 . Using the same brands of components too . I also posted a pic of the headshell with the Copper shielded I added . I didn't see it mentionned here but it is very important for this particular amp for cutting some particular hum noises
FYI I'm the guys who mods those preamps to Suhr's specs for over a decade now in EU
Cheers

Bruno

Sorry bumping this post but where did you get that Custom 22 Schematic ? Something looks weird to me .001 coupling cap with the same cap to ground just behind after 3rd gain stage of OD channel ?

Thx

Bruno

capota wrote:I don't think that anyone has the Custom 22 Schematics ))

who can help me to tame down the gain on the Lead channel?? I've Already changed the R6 from 220k to 110k (switchable) and changed the Slope resister (R26) from 47K to 33k (Marshall feel, also switchable). I want to make it a bit more Marshall flavor.

Also cut the C6 but it made it too much of a dark amp. What value for the C6 (Bright cap) do you guys recommend??

Thank You!!!



Here it is after the mods

Seems to me I saw it posted somewhere in the 38 pages here, but, I'd like to know if there is a consolidation of all the mods for the JCA 20H or 50H? I've got a power amp constructed and considering this preamp as possibility.

Great job here,

silverfox.

Hi @Bruno, it was sent to my by the owner of Jet City (Doug White), because I was one of the first to buy this amp (bought on November 2015) and had a little problem with the connections, so, in order to fix it, I needed the schematic with values.

I Have both the Pre and Power schematic.

new guys!

silverfox - see page 1, 3rd post for my consolidated reference list. Most everything is linked there.

capota wrote:Hi @Bruno, it was sent to my by the owner of Jet City (Doug White), because I was one of the first to buy this amp (bought on November 2015) and had a little problem with the connections, so, in order to fix it, I needed the schematic with values.

I Have both the Pre and Power schematic.

Hello

ok though there could be a mistake printed there ..There is a big one on the JCA22H service manual where the power tubes and preamp tubes heaters supplies are inverted
When you have a chance can you check C11 and see if it really is a .001 ?

Thanks

Bruno

Hi Guys, WOW this thread is immortal !!

Been a few years since I've been here, did the SLO mod on my 100HDM using Jay's specs back then and have been mega happy since.

Everytime I start to think about getting a new amp, I crank her up and when I hear that huge roar, I realise there is no way I'm parting with that, even these days with all the Friedman frenzy.

One thing though I would love to get from the amp ( rather than a pedal ) is to get a nice early breakup in the crunch channel, like some Hendrix type sounds.

At the mo it sounds only ok, but the breakup sounds 'wrong' , difficult to describe, its more of a 'hard' edge to it. My cheap assed Joyo American Sound pedal actually does a better job at it, and cleans up to a better clean too, however that means more stomping when switching to OD, which is something I don't want. I just want guitar, lead and amp.

I've Tung Sols in V1-V4 and a JJ in V5, would putting something like a Mullard in V1 bring me closer to what I'm after ?



Murph

So here's a funny thing... Since getting the 1x12 w/K-100, the cleans are pretty great on the Custom 22 but the OD sounds are more "meh". Not a biggie as I want to use it as a pedal platform.