JCA OWNERS!!! (RE)JOIN THE JET CITY LOUNGE!!!

[Hipster Salad]

Anybody know of any SLO style knobs? I've searched a few sites that carry collet style knobs but haven't searched them all, and have found some that are close, but not exact. I'd rather not pay $60 to get them from C3 Amps . . .

[bfgamps]

Righteous dude, right here!

Is that a JCA20 or 22 in your avatar? I dig the faceplates. Like a metalface Marshall. Sexy.

That amp is a 22H with a Jose type circuit on Channel 1 and a Aldrich type on Channel 2. A couple of great classic Marshall mods in one.

[Promit]

Hmm. Can someone hunt down a good knob on Mouser that is a pretty close match to the stock? I'm skimming through here but not really seeing anything. My depth knob is just a pot shaft right now.

Get the Dunlop style ones from here http://www.tubesandmore.com/products/P-K345 if you need one with a set screw to match. If you're using a pot that is a knurled shaft like the original ones PM your address and I'll send you some OEM ones...I have a few hundred laying around.

Brian

Awesome, thanks. I don't have a knurled shaft; it's an Alpha V38 pot with a smooth non-split shaft, so I guess I need the set screw version. Although idea of simply changing to chickenheads across the board is tempting too...

Also, on the subject of your amps -- how do you make the Marshall style faceplates? Is it something that's easy to do at home or does it require a bit more actual manufacturing?

[bfgamps]

I designed the faceplates and have them made for me. You can get the other style knobs from that same website.

Brian

[jhall]

I have a JCA 2112RC. Probably the stupidest $399.00 I ever spent on gear. Oh yeah add another
$80.00 or so bucks for JJs. I have NEVER liked or even been remotely happy with the sound of this amp.
It is VERY over compressed and muddies right up as the crunch level goes up. (I've heard some nice clips but I've not come CLOSE to any of those sounds)
I did the BitMo Gain and clean mods and was underwhelemed to say the least.

It's telling that when I was clearing out a bunch of amps on Craigslist that within 8 hours of posting I sold my Mustang-III, Blackstar HT-5h, Vox Valvetrinix 30 watt,
and a day later sold my Roland cube and the only amp that wasn't sold and only got an offer of an SD-1 in trade Is the Jet City.

[Promit]

LOL. DId the Jet City hurt your wittle feelings? I will grant you though, the resale sucks. Kind of a travesty that people prefer that Blackstar trash.

[jhall]

LOL. DId the Jet City hurt your wittle feelings? I will grant you though, the resale sucks. Kind of a travesty that people prefer that Blackstar trash.

Nah. I'm a big boy
Just not for me is all. Blackstars are not much to write home about either except
my HT-60 dual stage I bought new I actually made money on as I got it cheap new.
And when I unloaded it the buyer was very happy to have it and even e-mailed me about it months later.
I sold my HT-5h for $25.00 more than I paid for it. The only amps I ever made money off of.
But to me they weren't all that either.
The JCA proved useless to me. that's all. I'm just sharing my experience.
Again I'm not a rocket scientist when it comes to tweaking or imagination. I've seen many excellent youtube vids of JCA amps.

[Motocooney]

Lol. So this is where everyone went!

Apparently Harmony Central wasn't cool enough....

I love how you guys adopted the slope on a toggle and its now a voicing switch...awesome.

I tried a bunch of different values and finally just got rid of the switch. Left the 33k in there.

It just sounds best.

I think toggles are a good way to find out what you like the most. After that they just look cool cause they don't get switched any more.

Also, I agree with kasebrot on the r19/r46 150k/150k.
It just sounds best.

Sweet thread dudes!!!

[Jay]

Just got through an initial run with the MM PT in the JCA50H. I didn't get to play the amp in stock form since it had fried beforehand, but it sounds good. Harmonics are all over the place. I didn't get to play loud since my little ones are all sleeping, so I'll torture them tomorrow, maybe. I'll try and get a vid clip of some of my crappy playing. Just for kicks, I also slapped some TungSol 6550s in there for a few minutes. The difference from the JJ 6L6s is pretty drastic. Everything is just BIGGER sounding. It's so thick that you could probably taste the tones. Almost a little bit of a "fuzz" on the top end. I'm betting these amps will take to other tubes very well. KT88s should sound HUGE!

Keep in mind that I DID NOT make any changes to the power section of the amp. If you guys DO want to change PTs to accomodate these other tubes, it will be recommended to change the screen grids from 500ohms to 1k5-3k3 ohms, and possibly the control grids from 4k4 to 5k6. The screen grids are the most important, to keep the power tube screens from dissipating too much voltage and suffering premature failure.

Also, if you REALLY want to run EL34s, a connection for pin 1 will have to be made for the supressor grid at the tube sockets. IMO, you can get a little of that EL34 flavor with a set of KT77s, by JJ or Gold Lion. Both of those tubes are Tetrodes like the 6L6 and do not require the pin 1 connection. So, minimal modification to the power section will be required.

I'll post a write up soon, and then I'll be doing the SLO mod to this guy.

[Jay]

Started my write up on the PT install.

JCA 50H Mercury Magnetics PT install

I don't know which thread to put this in.

[Jay]

A few crappy clips with my Nikon camera, both of 6L6s and with 6550s. Left all the knobs where they were for all clips to get a raw comparison. Clips were done on the OD channel, gain at 5, TMB and presence at 5.....mids might be a little higher...6...maybe and volume at roughly 2~ish. Bias on the 6L6s is about 35mA, bias on the 6550s is about 45mA. Cab is a stock PV 5150 cab, guitar is a Les Paul Custom with Duncan Seth Lovers. Standard tuning. Nothing fancy.

NOTE: NO modifications was done to the Screen Grid resistors. In order to run tubes OTHER than 6L6s, some modifications must be done to the SGs in order to expect any kind of longevity of the power tubes. This is just for a raw comparison.

Test with JJ 6L6s:

[video]https://www.youtube.com/watch?v=pFbJ5fjSuCw[/video]

Test 1 with TungSol 6550s:

[video]https://www.youtube.com/watch?v=v26YYrvCybk[/video]

Test 2 with TungSol 6550s:

[video]https://www.youtube.com/watch?v=7JGzzHhksms[/video]

A dollar to whomever can name the Sabbath song that I was butchering.

[whitetrash529]

Just became a new JCA100H owner. Swapped the #1 with a Ruby and it cleaned up the fizz. But, so far I LOVE this amp. MY only concern is the clean channel has a fair amount of grit to it. Without having to read all 11 pages, any suggestions to make it purdy and sparkly? I am open to tube swapping but don't want to alter the crunch channel too terribly much. And, yes..I'm not the most knowledgable on this stuff

[Schweezly]

I also recently joined...picked up a 50H last week and just had a chance to put it through a full test yesterday at practice. A few thoughts:

-it seems to have more punch than my JVM. It also seems to have a little more low-mid presence and a brighter top end. Through my Orange 412, I had the treble at maybe 11am and the presence barely on. I loved the crunch at about 8 on the gain, and OD at about 2.5

-I'm torn between the 2 "channels". Speaking of which, I'm very confused by how they work. The "crunch" volume doesn't seem to do anything. It doesn't matter if I use the crunch or the overdrive gain...only the OD volume does anything. Is this an issue with the amp, or am I just lost? I also plugged in a generic channel switch and it didn't switch. Maybe I should read a manual

-I liked it overall, but it seemed like it might have been a little lost at times. I've got 2 gigs this weekend so I might run each amp at one and see what I think. I loved the punch and some of the dynamics, but I feel some things were lost in the middle.


My JVM is currently stuck in clean red mode, which is dark and not my favorite mode. That one of the reasons I grabbed this (I've got 6 gigs in July). We'll see if I end up sticking with both.

[Tortuga]

A few crappy clips with my Nikon camera, both of 6L6s and with 6550s. Left all the knobs where they were for all clips to get a raw comparison. Clips were done on the OD channel, gain at 5, TMB and presence at 5.....mids might be a little higher...6...maybe and volume at roughly 2~ish. Bias on the 6L6s is about 35mA, bias on the 6550s is about 45mA. Cab is a stock PV 5150 cab, guitar is a Les Paul Custom with Duncan Seth Lovers. Standard tuning. Nothing fancy.

NOTE: NO modifications was done to the Screen Grid resistors. In order to run tubes OTHER than 6L6s, some modifications must be done to the SGs in order to expect any kind of longevity of the power tubes. This is just for a raw comparison.

Test with JJ 6L6s:

[video]https://www.youtube.com/watch?v=pFbJ5fjSuCw[/video]

Test 1 with TungSol 6550s:

[video]https://www.youtube.com/watch?v=v26YYrvCybk[/video]

Test 2 with TungSol 6550s:

[video]https://www.youtube.com/watch?v=7JGzzHhksms[/video]

A dollar to whomever can name the Sabbath song that I was butchering.

Jay - sorry I didn't get to this until now. Got busy with kids' scout camp, holiday, and studio building (yes, it's happening - 3 walls are up, and a new thread will be posted as soon as I can!)...

Just listened to a few seconds of you playing Into The Void on the last clip (don't want your dollar - just continue the stellar jca work!). Can't wait to listen to it on a proper speaker setup later today. Any chance that you will detail the needed mods for allowing different tubes to run reliably?

[Jay]

I also recently joined...picked up a 50H last week and just had a chance to put it through a full test yesterday at practice. A few thoughts:

-it seems to have more punch than my JVM. It also seems to have a little more low-mid presence and a brighter top end. Through my Orange 412, I had the treble at maybe 11am and the presence barely on. I loved the crunch at about 8 on the gain, and OD at about 2.5

-I'm torn between the 2 "channels". Speaking of which, I'm very confused by how they work. The "crunch" volume doesn't seem to do anything. It doesn't matter if I use the crunch or the overdrive gain...only the OD volume does anything. Is this an issue with the amp, or am I just lost? I also plugged in a generic channel switch and it didn't switch. Maybe I should read a manual

-I liked it overall, but it seemed like it might have been a little lost at times. I've got 2 gigs this weekend so I might run each amp at one and see what I think. I loved the punch and some of the dynamics, but I feel some things were lost in the middle.


My JVM is currently stuck in clean red mode, which is dark and not my favorite mode. That one of the reasons I grabbed this (I've got 6 gigs in July). We'll see if I end up sticking with both.

Well, to start things off, the two channels bleed into each other a bit, so you get a little crunch on the OD. And redorkulously enough, there is NO switch on the front panel as a hard bypass. So, unless you have the footswitch, you can't switch between Crunch and OD. I put up a little mod in the DIY section to install a toggle for the channels if you would like to have the ability to switch channels without the foot controller.

[mjtripper]

Hey and howdy. I recently purchased a used jca22h to tinker with and am on a few other boards but thought I would pop over here and check out some jet city specific action. I saw a number of threads but is there a jca22h specific mod thread?

[Jay]

Just became a new JCA100H owner. Swapped the #1 with a Ruby and it cleaned up the fizz. But, so far I LOVE this amp. MY only concern is the clean channel has a fair amount of grit to it. Without having to read all 11 pages, any suggestions to make it purdy and sparkly? I am open to tube swapping but don't want to alter the crunch channel too terribly much. And, yes..I'm not the most knowledgable on this stuff

I'll have to check pin configurations, but a JJ ECC832 or ECC823 in V1 might work to lower the gain a bit for the crunch channel if you don't want to swap resistors and caps.

[Jay]

Hey and howdy. I recently purchased a used jca22h to tinker with and am on a few other boards but thought I would pop over here and check out some jet city specific action. I saw a number of threads but is there a jca22h specific mod thread?

Same stuff applies to the Preamp of the 22H, 50H and 100H/HDM. The 22H just seems to have different callouts for the cap and resistor locations.

[Tortuga]

I also recently joined...picked up a 50H last week and just had a chance to put it through a full test yesterday at practice. A few thoughts:

-it seems to have more punch than my JVM. It also seems to have a little more low-mid presence and a brighter top end. Through my Orange 412, I had the treble at maybe 11am and the presence barely on. I loved the crunch at about 8 on the gain, and OD at about 2.5

-I'm torn between the 2 "channels". Speaking of which, I'm very confused by how they work. The "crunch" volume doesn't seem to do anything. It doesn't matter if I use the crunch or the overdrive gain...only the OD volume does anything. Is this an issue with the amp, or am I just lost? I also plugged in a generic channel switch and it didn't switch. Maybe I should read a manual

-I liked it overall, but it seemed like it might have been a little lost at times. I've got 2 gigs this weekend so I might run each amp at one and see what I think. I loved the punch and some of the dynamics, but I feel some things were lost in the middle.


My JVM is currently stuck in clean red mode, which is dark and not my favorite mode. That one of the reasons I grabbed this (I've got 6 gigs in July). We'll see if I end up sticking with both.

Well, to start things off, the two channels bleed into each other a bit, so you get a little crunch on the OD. And redorkulously enough, there is NO switch on the front panel as a hard bypass. So, unless you have the footswitch, you can't switch between Crunch and OD. I put up a little mod in the DIY section to install a toggle for the channels if you would like to have the ability to switch channels without the foot controller.

Couldn't he plug a known working cable into the footswitch jack and test changing channels from OD to crunch by shorting the tip to chassis ground (touch tip to metal nut on any jack)? Just a thought, although I do recommend installing a channel switch as discussed earlier in this thread, provided his amp is working correctly, as this test would bear out.

[Jay]

I also recently joined...picked up a 50H last week and just had a chance to put it through a full test yesterday at practice. A few thoughts:

-it seems to have more punch than my JVM. It also seems to have a little more low-mid presence and a brighter top end. Through my Orange 412, I had the treble at maybe 11am and the presence barely on. I loved the crunch at about 8 on the gain, and OD at about 2.5

-I'm torn between the 2 "channels". Speaking of which, I'm very confused by how they work. The "crunch" volume doesn't seem to do anything. It doesn't matter if I use the crunch or the overdrive gain...only the OD volume does anything. Is this an issue with the amp, or am I just lost? I also plugged in a generic channel switch and it didn't switch. Maybe I should read a manual

-I liked it overall, but it seemed like it might have been a little lost at times. I've got 2 gigs this weekend so I might run each amp at one and see what I think. I loved the punch and some of the dynamics, but I feel some things were lost in the middle.


My JVM is currently stuck in clean red mode, which is dark and not my favorite mode. That one of the reasons I grabbed this (I've got 6 gigs in July). We'll see if I end up sticking with both.

Well, to start things off, the two channels bleed into each other a bit, so you get a little crunch on the OD. And redorkulously enough, there is NO switch on the front panel as a hard bypass. So, unless you have the footswitch, you can't switch between Crunch and OD. I put up a little mod in the DIY section to install a toggle for the channels if you would like to have the ability to switch channels without the foot controller.

Couldn't he plug a known working cable into the footswitch jack and test changing channels from OD to crunch by shorting the tip to chassis ground (touch tip to metal nut on any jack)? Just a thought, although I do recommend installing a channel switch as discussed earlier in this thread, provided his amp is working correctly, as this test would bear out.

Yes! Yes he could. Good idea!

[Jay]

Oh, and to use other tubes besides 6L6s, the SG resistors would need to be bumped from 500R up to someting in between 1k5-3k3. 2k2 would be a happy medium. EL34s would require a bit more change to the tube socket. If you really want EL34s, just try KT77s.

[Schweezly]

I also recently joined...picked up a 50H last week and just had a chance to put it through a full test yesterday at practice. A few thoughts:

-it seems to have more punch than my JVM. It also seems to have a little more low-mid presence and a brighter top end. Through my Orange 412, I had the treble at maybe 11am and the presence barely on. I loved the crunch at about 8 on the gain, and OD at about 2.5

-I'm torn between the 2 "channels". Speaking of which, I'm very confused by how they work. The "crunch" volume doesn't seem to do anything. It doesn't matter if I use the crunch or the overdrive gain...only the OD volume does anything. Is this an issue with the amp, or am I just lost? I also plugged in a generic channel switch and it didn't switch. Maybe I should read a manual

-I liked it overall, but it seemed like it might have been a little lost at times. I've got 2 gigs this weekend so I might run each amp at one and see what I think. I loved the punch and some of the dynamics, but I feel some things were lost in the middle.


My JVM is currently stuck in clean red mode, which is dark and not my favorite mode. That one of the reasons I grabbed this (I've got 6 gigs in July). We'll see if I end up sticking with both.

Well, to start things off, the two channels bleed into each other a bit, so you get a little crunch on the OD. And redorkulously enough, there is NO switch on the front panel as a hard bypass. So, unless you have the footswitch, you can't switch between Crunch and OD. I put up a little mod in the DIY section to install a toggle for the channels if you would like to have the ability to switch channels without the foot controller.

Couldn't he plug a known working cable into the footswitch jack and test changing channels from OD to crunch by shorting the tip to chassis ground (touch tip to metal nut on any jack)? Just a thought, although I do recommend installing a channel switch as discussed earlier in this thread, provided his amp is working correctly, as this test would bear out.

Hmmm, I'd be interested in both the test and a switch. I'm more confused/concerned about why I can't find any use for the "crunch" volume. It doesn't matter which gain knob I use, only the OD volume controls volume (and I don't remember that being the case when I tested it)

I tested at gc on a Wednesday night, had to run and came back an bought it Friday. I was in a hurry and didn't test again, but I've got a few weeks if there turns out to be an issue

[mjtripper]

Hey and howdy. I recently purchased a used jca22h to tinker with and am on a few other boards but thought I would pop over here and check out some jet city specific action. I saw a number of threads but is there a jca22h specific mod thread?

Same stuff applies to the Preamp of the 22H, 50H and 100H/HDM. The 22H just seems to have different callouts for the cap and resistor locations.

True, just didn't want to clutter up the place. The 22 has the fx loop post master like the hot rod 25 has which is what drew me to that one over the others. It uses relays instead of ldrs though so makes moving those connections a little more time consuming. Here are some board shots I took before I started working on it. There is also an error in the schematic that is probably already posted in some thread but c30 and r54 are on the board and parts list but missing from the schematic. They are connected similar to c3 and r11 but feeding the fx loop instead. On the schematic the line coming from R33 to point A should instead go to the junction of C30 and R54 which aren't shown.

[mjtripper]

Here is an after / in progress shot. The normal channel is a clean channel now with no bleed from the overdrive channel. The bleed really isn't too bad stock until you start to want a clean channel and as you clean it up the bleed gets annoying, at least for me. The OD voicing changes are just to give it a little of a british flavor and to tighten the low end a little. Some changes are just to reduce noise. I swapped out some components just to a different brand but kept the value just because I had them. I bought this used and had to fix a trace as well as replace the foot switch jack so while I was in there anyway I removed it from the pcb in case it fails again and wired in a front panel normal/od switch.

R2 = 10k
Add 620pF between V1-7 and V1-8
C2 = 10nF
R6 = 100k-3w
Add 47K to ground between R5 and normal gain
R4 = 1.5k
Add 4.7uF as R4 bypass
C7 = 120pF
R10 = replace with 2 1M split with 1000pF to ground
Remove R20
R9 = 470k
C5 = 2.2nF
C6 = 620pF
C9 = 10nF
R18 = 470k
R16 = 15k
Add 270k in series/after C11
R26 = 39k
Add 10nF snubbers to D1-D4
Move relay connection from grid of 3rd od stage to 2nd od stage

[Jay]

Sweet, man! Looks good! Welcome aboard!