Guitar Gear Forum

Yeah, I managed to lurk around the thread a bit before the pics disappeared. I've been having trouble finding the definitive answer on the pilot light though. I replaced the original faulty one, Doug White was really helpful getting the replacement. But I was looking into replacing it with a more traditional socket and bulb. If I'm understanding correctly, it's a straight swap with some widening of the hole being necessary. Is this correct?

hi, been a long time since i've been on. getting back into modding my jca22 and jca50. i'm going to do the slo mod on the jca50 and i'm going to convert the jca22 lead channel to a rectifier red channel. i'll post under my jca2212c mod thread. any questions or suggestions welcome.

thread link:
viewtopic.php?f=53&t=15610

xmugmugmugx wrote:I figured I'd throw another question out there and see if anyone has an idea. My apologies if it's been answered already. So I'm looking at the JCA2112rc schematic and there are 2 extra tubes vs the JCA20H. Now I know that one of them is for the reverb. But V2 seems to also be going primarily to the reverb stage section as well. What I'm trying to sort out is the Marshall 2204 conversion, which I believe was originally done on a JCA20H. Does anyone have experience with the 2112rc and how to approach this mod?

I also just wanted to say that I'm already enjoying this thread and learning quite a bit. Thank you everyone.

It has two more tubes for reverb as the description online for the amp states. The first two tubes are all that matter. The signal path in the first two tubes is pretty much identical to a jcm800. Which makes for a very straight forward conversion.

Thanks Shep. That's what I figured. I really like the combo and wanted to make sure I didn't have to make any extra considerations when applying mods.

Good to have you back, Shep

xmugmugmugx wrote:Thanks Shep. That's what I figured. I really like the combo and wanted to make sure I didn't have to make any extra considerations when applying mods.

I just ordered a jca custom 5. If it's the same as the Pico valve or jca20h, I'm going to do the jcm800 mod as well.

shep wrote:I just ordered a jca custom 5. If it's the same as the Pico valve or jca20h, I'm going to do the jcm800 mod as well.

When I first got the combo, I was happy, but felt like something was missing. I started looking into the mods that were out there. When I learned how close the Jet City was to a JCM 800, I was ecstatic.

xmugmugmugx wrote:

shep wrote:I just ordered a jca custom 5. If it's the same as the Pico valve or jca20h, I'm going to do the jcm800 mod as well.

When I first got the combo, I was happy, but felt like something was missing. I started looking into the mods that were out there. When I learned how close the Jet City was to a JCM 800, I was ecstatic.

Yeah, I built a plexi se pcb amp with the jcm800 option a while back and it was awesome. I wanted another one. My options were to Build one for 200 bucks or buy the custom 5 for $140 and 10 bucks in parts. I'm choosing the latter. Besides, after building the jcm800 clone, I realized how awesome the jcm800 was for hard rock.

Hi guys!

I'm a fresh owner of a JCA50H and i was wondering:

1. if its possible to get delay pedal that would work in a FX LOOP of that amp?
2. and if that delay had built-in boost, would it get my amp a lil' bit louder? or just amplify the delays

I'm thinking about some kind of a quick jump to soloing mode, with delays and overall volume boost so my solo wouldn't hide under second guitarist's riffs.
I've tried Digitech Hardwire in the fx loop (listed as compatible with jca fx loop on that board) but it sucked the power from the distortion : (

There should be several delays on the list (page 1 of this thread) that can handle the line-level output in the 50's loop. Pretty sure my old TC Flashback worked well.

I've tried boosting the loop level on my 50 as you describe, using an MXR MicroAmp and MXR EQ10. The MicroAmp did a good job, but I had some distortion with the eq. I've also heard of guys using volume pedals in the loop to do things in reverse - set a minimum level for normal playing and then open it up for solo. The 50 should have plenty of volume available, so this may accommodate your needs.

Gotta jca custom 5. Anyone posted any info about these? Can't find a schematic or much info at all.

Cracked it open! Similar to the Pico valve. Mid/fat switch appears to switch cathode bypass caps for v1a and v1b. Have a choice between 4.7uf/nothing/.47uf.it's two 4.7uf and two .47uf caps for both cathodes. So many tinkering things I can do with this!!.

My first idea is to jcm800 this baby, then have resistors across the caps of these switch positions with 1uf caps instead of what it comes with to get a bit more gain and that slo sound. Thoughts?

update: made the schematic for the jca custom 5. gut shots

Would love to check one out. Got any clips?

Please do send gut shots - I'll post 'em up when things get sorted out with the photobucket debacle. I'll pm my email in a minute.

So I've been pouring over schematics of the JCA20 and JCA2112 and noticed R14 & R15. Now I understand that these amps are similar to the JCM800, with some alterations. But what is the purpose of these resistors? The JCM800 doesnt have resistors following the tone stack.

jca22h/rectifier mod parts list (mouser bom):

273-680K-RC
71-CCF02-F-220K
594-2222-375-26222
594-2222-375-14102
75-561RU2JQA102EC200
594-S501K29X5FN63L6R

jca50h with slo mod.

sound clip

single track, double tracked, then with lead.

https://www.youtube.com/watch?v=5cokraa ... e=youtu.be

So I bought some tubes to try on my jca22h, but I'm having some trouble removing the front baffle to easily access the tubes and swap them. I already removed the back panel, but now I can't access the screws that are down on both sides. See images





I'm guessing I'll have to remove the chassis so I can easily unscrew the front baffle and them remount the chassis (I know I could do the swapping and testing with the chassis out but I'd feel safer that way).

Any insight? Also how easy it is to remove the shields on V1 and V2? They seem kinda stuck. Thanks, I'm a total noob.

I got impatient and went for it. I had to remove the chassis to get to those screws. I was a bit fearful with messing with the chassis since I've got no experience with electronics but I guess I was overthinking.

I had read multiple times how important it was to change tubes and how crappy the Chinese were, but man I wasn't expecting this kind of difference. For reference I put a Sovtek Lps in V5, JJ 12ax7 in V4 and V3 and went back and forth with a selected Tung Sol 12ax7 reissue and a selected JJ 12ax7 in V1 and V2. They were pretty different. The Tung Sol being more open and sharp and the JJ darker and beefier (as expected) and apparently nosier. I ended up with the JJ in V1 and the Tung Sol in V2, but I'll get back to it in a week or so.

Also this made me realize that I need to change that front panel for something better aesthetically and easier to remove.

putting the noisier tube in v1 will make it even more noisy because that is the most sensitive tube in the amp. whatever signals get introduced and amplified by this tube are re-amplified through the other tubes the most times within the amp.

not sure why you had to take the front baffle off. never had to do that to an amp to change the tubes. i just did it through the back.

shep wrote:putting the noisier tube in v1 will make it even more noisy because that is the most sensitive tube in the amp. whatever signals get introduced and amplified by this tube are re-amplified through the other tubes the most times within the amp.

I spent about 1 hour going back and forth with those two tubes in V1 and V2. Neither sounded bad, just very different. I eventually got tired and stuck with the JJ in V1 and Tung Sol in V2. In a way the JJ darker nature sounded like it complemented well the brightness of the amp, to my hears. The Tung Sol took the amp natural characteristics and just made it sound better, which I loved also. I said the JJ sounded a little bit noisier than the Tung Sol, but not a whole lot noisier. In fact the JJ itself is quieter than the stock tubes. Note that both got rid of fizzyness and harsh frequencies and added more body to the sound, it just sounds more organic. I'll stick to this configuration for a while, in a couple weeks I'll change it and see and suits me better.

shep wrote:not sure why you had to take the front baffle off. never had to do that to an amp to change the tubes. i just did it through the back.

have you ever changed tubes in the 22h? It's possible to do it without removing the front baffle, but it's a pain in the ass to do it from the rear. Especially if you'll spend a lot of time swapping in V1.

completed the rectifier mod on my jca22. sounds pretty sweet.

sound clip: https://youtu.be/EDXRtOOam_4

The Amp Factory had the vintage speaker for under $50, no tax, free shipping. I figured for that price, I might give it a go since I was looking at speakers from Eminence that are like this.

http://www.ampfactory.com/jv12-16-ohm/

As far as the bulb, any T3 1/4 inch will work. I got one from radioshack on clearance. I may ask for
a relplacement to ship with my speaker.

So I have read a lot of information about swapping values of the slope resistor to get a Marshall sound, but could you use the same logic to get an Orange sound? I know the basic structure of Orange amps would limit how effective this would be, because Orange tone stacks come off the plate. Just curious.

So I did the speaker swap today. This was
by far the easiest and most effective change to the amp. I am impressed with how much more the amp responds to pick attack and touch than before. In addition, the mids are much more present and the trebles are clearer. The vintage speaker seems to be a 55 watt version of the Eminence CV-75. The magnet is huge, at 56oz. This was the best money I have invested in the amp, and the speaker is not even broken in yet.

mbranford wrote:So I did the speaker swap today. This was
by far the easiest and most effective change to the amp. I am impressed with how much more the amp responds to pick attack and touch than before. In addition, the mids are much more present and the trebles are clearer. The vintage speaker seems to be a 55 watt version of the Eminence CV-75. The magnet is huge, at 56oz. This was the best money I have invested in the amp, and the speaker is not even broken in yet.

I've been rocking the Jet City Vintage speakers for a year now, and they are pure sleepers. I still can't believe how great they sound, regardless how cheap they are.