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

[Tortuga]

Man - what can be better than a guy from Istanbul that combines Spock and Iommi



Yup - lots of info to digest, but the ref on the first page pretty much tells you where the important stuff is. Glad to have new blood, and new interest!

[Jay]

Hi guys! Greetings from Istanbul! I think i found a heaven here as a 40 years old Rock'n Roll and GASer pagan.

When i was looking for a good amp -and of course for a reasonable price, i bought a Jet City JCA50 from Thomann. I saw a couple of videos. Some much of them had influenc upon my decision. And later, a JC video brought me here. After a few messages under the "JCA50H with Mercury Magnetics PT and TungSol 6550s" video of Jay on YT, i registired. Especially for JC topics. I am glad to see this online lodge. 30 pages to read. Thanks to GRIMESPACE, GuitarBilly and Jay for this club, sharing and guiding.Now, so much pages to read and learn.

Live Long And Prosper!

_\\//

H

Good to see you made it over here, dude. Take it all in, it goes down smooth.

[Jay]

I'm a huge fan of the depth mod and slope resistor (mine switches between stock & modded values). The clean switch is ok - just don't expect the world. It gives you a decent clean, but it seriously drops the volume from the regular crunch output.

A bunch of guys have done the SLO mod. I don't think there's been anybody that's been unhappy with that one. Right now, I'm debating selling my JCA ( ) - my new Marshall DSL is that good - but if I keep it, I'll probably be doing the SLO mod to see if it's a keeper for the higher-gain, more modern tone.

I did the heater mod, pretty much the same as shown earlier in the thread. I don't feel like I got a massive reduction, but it's a little better. If I had it to do over, I'd probably skip it. midnightlaundry talked up changing the rectifier diodes, and I'd like to give that a shot some time. Also, I think the best thing to do would be converting the preamp heaters to DC, but that's a pretty extensive change (likely an upgraded PT) if you don't want to resort to a secondary thing to plug in (I sure don't).

If you haven't done so, definitely change out power tubes, P1, P2, and P5 (probably best to do P3 and P4, since its only $20 more), and set bias correctly.

Good luck!

What heater mod did you do? Also, to change the heaters to DC shouldn't be to hard, but I need to loo at one of the bigger amps again. My buddy is getting weird hums on his three JCA amps, so I'm sure I will be doing some kind of mod to quell the issue. lol

[Tortuga]

Cut traces at all 12ax7 tubes - then installed bell wire that had been twisted per the postings from Big John and midnightlaundry.

My understanding is that there's not enough power available from the PT to support running any kind of AC-DC converter. There was one person that put an adapter in that used a separate 120v plug, but that really doesn't interest me.

Definitely curious as to what you come up with, Jay. Great to see you're alive!



>>>edited for stupidity - it's not the power tube traces I cut, dammit! <<<

[Jay]

Cut traces at all 12ax7 tubes - then installed bell wire that had been twisted per the postings from Big John and midnightlaundry.

My understanding is that there's not enough power available from the PT to support running any kind of AC-DC converter. There was one person that put an adapter in that used a separate 120v plug, but that really doesn't interest me.

Definitely curious as to what you come up with, Jay. Great to see you're alive!



>>>edited for stupidity - it's not the power tube traces I cut, dammit! <<<

Haha. I'm still alive, just been very busy.

Two things aside from cutting traces: Remove the heater for the preamp section, then get a separate filament transformer and set up a DC regulator circuit for the preamp heaters. Or set up a DC regulator with the stock filament heater and take a higher voltage reference from the mains.

If you go about using a small filament transformer, you can just hook it up to the mains switch and mount it inside. Then, you can also get one with a heightened voltage to keep the vHk differential up to make the cathode followers happy.

IE: the tubes that are being used in a cathode follower position expose the cathodes to very high voltages. These amps run the CF at 200+ volts. The stock heater is at 6.3v. The vHk (V-voltage H-heater K-cathode) differential in a 12AX7 is typically 180 volts. if the cathode is at 200 and the heater is 6.3, then the difference is 193.7. Just a little higher than the 180 rating, but some of the Sovtek tubes do NOT fare well with these increased voltages. Sometimes you will get odd intermittent mechanical noises like pops, swirls and hissing. Long plate tubes are most prone to failure in these positions. JJs and Chinese tubes seem to be the most robust to me so far. If you raise the heaters up to say, 50v or so with a DC reference, some instances eliminates ANY trace of hum, hiss, or any other EMI, AND the tubes will tend to last longer.

[Tortuga]

Cut traces at all 12ax7 tubes - then installed bell wire that had been twisted per the postings from Big John and midnightlaundry.

My understanding is that there's not enough power available from the PT to support running any kind of AC-DC converter. There was one person that put an adapter in that used a separate 120v plug, but that really doesn't interest me.

Definitely curious as to what you come up with, Jay. Great to see you're alive!



>>>edited for stupidity - it's not the power tube traces I cut, dammit! <<<

Haha. I'm still alive, just been very busy.

Two things aside from cutting traces: Remove the heater for the preamp section, then get a separate filament transformer and set up a DC regulator circuit for the preamp heaters. Or set up a DC regulator with the stock filament heater and take a higher voltage reference from the mains.

If you go about using a small filament transformer, you can just hook it up to the mains switch and mount it inside. Then, you can also get one with a heightened voltage to keep the vHk differential up to make the cathode followers happy.

IE: the tubes that are being used in a cathode follower position expose the cathodes to very high voltages. These amps run the CF at 200+ volts. The stock heater is at 6.3v. The vHk (V-voltage H-heater K-cathode) differential in a 12AX7 is typically 180 volts. if the cathode is at 200 and the heater is 6.3, then the difference is 193.7. Just a little higher than the 180 rating, but some of the Sovtek tubes do NOT fare well with these increased voltages. Sometimes you will get odd intermittent mechanical noises like pops, swirls and hissing. Long plate tubes are most prone to failure in these positions. JJs and Chinese tubes seem to be the most robust to me so far. If you raise the heaters up to say, 50v or so with a DC reference, some instances eliminates ANY trace of hum, hiss, or any other EMI, AND the tubes will tend to last longer.

I like where you're going with that, and may be really interested in pursuing it. Are you up to diagramming it out & pointing me to some parts? The DC regulator is going to be a rectifier (diodes), and some caps, right? I'm going to be putting a parts order together in the next few weeks for my old Fender amp that I'm going to rebuild this summer - it'd be great to put these parts in with the order (along with what I need for the SLO mod).

Really good to hear from you, Jay. BTW, what's a fair $$$ amount for the tubes you sent me many moons ago? I want to get that taken care of Do you think any of those tubes might work out in my new DSL?

[Jay]

I can probably put together a good list for you. Most regulators would be an IC chip, some diodes, caps and a few resistors. Something small that would fit inside the chassis under the PT.

What kind of Fender is it? Was it the '66 Bassman?I just did a lot of work to my friend's 1972 Silverface Twin. Replaced the big filter caps, installed a new verb tank and rewired the speakers.

As far as the tubes, what did I send you? I can't remember,

[Tortuga]

Lets do this! DC heaters & SLO mod sound like a plan to me

Fender is '73 Pro Reverb. Probably looks nearly identical to what you just went through, just on a somewhat smaller scale - smaller OT, 2x6L6 (rated at 40 watts). Biggest difference is the tube rectifier. Mine is pretty much bone stock (including tubes), except for a volume pot that I had to replace and one of the (crap, anyway) Utah speakers that I tossed because the core was grinding. Original owner is a really good friend and gave it to me, because it's a bit rough. I'm pretty sure that volume pot was sheared off when it took a header with a guitar cable plugged in. Actually dented the chassis and damaged the front panel pretty good. I'm planning to replace pretty much all the electrolytics and some of the resistors as needed per the Fender amp book I'm reading. I'm pretty set on building it into a headshell (so it's not taking up so much room in my studio) with a replacement panel that Mojotone is going to make for me, and will be blackfacing (primary focus on bias & PI circuits) as well as doing a couple of mods.

Would love to see the work you did in the twin, if you got pics. How'd it turn out?

I'll dig up the list of tubes as soon as I can. I'm leaving tonight for a week in DC (biz / fun trip).

[Jay]

SLO mod.....EPIC. So much more clarity. I think it will separate the JCA from the DSL some more.

Ill see if I can ind pics of the Twin. BIG fugger. All original glass too. So sweet.

Sounds like you got a handle on that Pro, mang!

[Tortuga]

I've learned a ton from talking to you, edge11,and a few others here, as well as the Fender amp book I bought, so I'm feeling comfortable with the project. That said, I reserve the right to reach out to you with questions

[Hipster Salad]

Alright guys, I got myself a GoPro last week. Since I had the day off work Friday, I decided to test it out a little. Trying to find time to do a more in depth demo, but here's a quick clip of the Earhart:

Trivia question: How many Jet City products do you spot?

[video]https://youtu.be/C2VnHcc_p0Q[/video]

[hackeiommi]

Alright guys, I got myself a GoPro last week. Since I had the day off work Friday, I decided to test it out a little. Trying to find time to do a more in depth demo, but here's a quick clip of the Earhart:

Trivia question: How many Jet City products do you spot?

[video]https://youtu.be/C2VnHcc_p0Q[/video]

Is this the price champion (2500 dollar) JC? I heard that Earhart amps are not producing anymore.

PS: I count nine JC products, can't see the speakers What do you think about Jettenuator?

[Hipster Salad]

Alright guys, I got myself a GoPro last week. Since I had the day off work Friday, I decided to test it out a little. Trying to find time to do a more in depth demo, but here's a quick clip of the Earhart:

Trivia question: How many Jet City products do you spot?

[video]https://youtu.be/C2VnHcc_p0Q[/video]

Is this the price champion (2500 dollar) JC? I heard that Earhart amps are not producing anymore.

PS: I count nine JC products, can't see the speakers What do you think about Jettenuator?

Correct on 9! Yes, that's the Earhart. Only 2 were built. My desert island amp for certain.

[hackeiommi]

Alright guys, I got myself a GoPro last week. Since I had the day off work Friday, I decided to test it out a little. Trying to find time to do a more in depth demo, but here's a quick clip of the Earhart:

Trivia question: How many Jet City products do you spot?

[video]https://youtu.be/C2VnHcc_p0Q[/video]

Is this the price champion (2500 dollar) JC? I heard that Earhart amps are not producing anymore.

PS: I count nine JC products, can't see the speakers What do you think about Jettenuator?

Correct on 9! Yes, that's the Earhart. Only 2 were built. My desert island amp for certain.

Only 2? And one of them is yours? Man, its awesome!! Waiting for new demos!

[hackeiommi]

Idk, shall i write here or start new thread. I am searching net since three days but couldn't find, see an answer. As a JCA user, i borrowed a Zoom 9150 Valve DSP rack processor to use in Fx Loop for effects. So far so good. But there is one thing concerns me. When i am playing, "Clip Level" light is always shining red and according to manual, it means "preamp is overloading by peak signal" But when i am playing, i can't hear any deterioration or corruption. What to do? Can i buy this unit or look for another one?

If inside the forum have an answer and i missed that, a link will be enough.

[hackeiommi]

Found a solution. I am turning input volume pot down till 9 o'clock. Red light is not shining anymore. After the years i forgot somethings about rack units

[BowerR64]

I got a used JCA50H from guitar center, the LED on the footswitch never has worked. I messed around it it the other day and thought i had it fixed.

It was reading 16v on one end of the resistor the other side nothing so i started playing around with resistors and found one that was about half the value of what is in there and it started working.

Then it went out again. Im wondering if maybe the little transformer is bad? What supplies voltage to the LED? the big transformers are for the power for the tubes right? and the little one in the front is for the electronics?

How do i check a transformer?

[ironman28]

The LED on the foot switch is powered by the 12V relay winding on the power transformer.
If the foot switch is working and you can switch between crunch and overdrive the relay winding is probably fine.
It sounds like you have a bad LED. Keep the original resistor value and try a new LED and or a new resistor.
The "little transformer" is the screen supply choke not a transformer. All the power supply voltages, B+, filament and relays are supplied by the big power transformer

[dfine22]

Hello Newbie here. I just picked up a JCA 22 combo. I am hoping to mod the amp.I have been trolling this thread for a couple of days now and it is long not to mention a little ADD on my part. I need a little help and I am sure these mods have been covered numerous times. I am basically going to change the slope resistor (R26)with a DPDT switch with 33k and 47K values. Is R26 the correct resistor? I am also going to add a choke at R52. Is this correct? Also a depth mod which I am good with. Thanks in advanced for any help, David

On a side note, has anyone done or know of the Bitmo/Surfa mod which sells on ebay??

[Tortuga]

Hello Newbie here. I just picked up a JCA 22 combo. I am hoping to mod the amp.I have been trolling this thread for a couple of days now and it is long not to mention a little ADD on my part. I need a little help and I am sure these mods have been covered numerous times. I am basically going to change the slope resistor (R26)with a DPDT switch with 33k and 47K values. Is R26 the correct resistor? I am also going to add a choke at R52. Is this correct? Also a depth mod which I am good with. Thanks in advanced for any help, David

On a side note, has anyone done or know of the Bitmo/Surfa mod which sells on ebay??

Hiya & .

Can't verify the slope resistor number, but according to the schematic I have, it does appear to be R26 on the JCA 22. I advise you to look up the relevant postings on page 1 of this thread - there's links to the schematics as well as the slope resistor mod that CTN and I did on our 100H & 50H (respectively).

Not sure which resistor gets swapped for the choke, but there have been discussions in the JCA20 threads that Edge did, and I found a couple of articles through a quick google search. Here's one that seems to confirm your question (R52): http://toboy-diy.blogspot.com/2013/10/jet-city-jca22h-choke-mod.html.

We'd greatly appreciate any postings regarding the mods that you do, and what the outcome sounds like.

As to the Bitmo/Surfa mod, all I can say is that I heard about it a few years ago. Some people tried them out with mixed results. Not sure at all what they attempt to do, so can't say one way or another how well they work out. Sorry, but many of the mods I've referenced on the first page are definitely of good standing.

I wouldn't bother doing any of the mods until you've addressed the tubes and bias. That's always the place to start - many have been satisfied with the improvements from those changes, alone.

And, lastly, please make sure you heed the warnings about knowing what you're doing before you even think about opening up the chassis. I'm always happy to help, but I need to know your next of kin's not gonna be hunting me down for advising you to do something that can seriously kick your ass into the afterworld. I need to know you understand how to safely work on these amps (discharging filter caps, keeping fingers and conductive tools out of harms way, etc.).

[dfine22]

Thanks GRIMSPACE (Face painter Seinfeld, love it )

I have swapped out the Eminence for a Creamback as well as the tubes (i'll report back on my final decision re; the tubes). I will take heed regarding voltage discharge.

[Tortuga]

How do you like it with the creamback? I tried my JCA50H with my 4x12 greenback cab, and found it overly harsh / bright. My Marshall head is way better with that cab.

[Pwrmac7600]

New jet city owner here. Recently purchased a JCA 22H and had it shipped directly to BFG. Brian has it now performing his 20lb hammer mod, adding a Mercury Magnetics OT, and choke. And a slew of other mods. Can't wait to get it back!
It should be a tone monster!!!
Looking around trying to figure out how to wire in LEDs into it, as I am making my expanded metal baffle now and would like to light the whole thing up.
Will post photos as soon as I get the amp back from Brian in about two weeks.

[HavPT]

Hi guys I'm new here and found this thread today, I'm about to buy a JCA100HDM amp + JCA24s cabinet bundle. Can someone pls tell me if the digitech multifx RP1000 will work fine on 4 cable method, this is mostly to use the amp loop with some effects running on the amp fx loop. Has anyone tried this or know if it will gonna work?


Thanks

[Tortuga]

Hiya - not sure about that effects unit, although I did have luck with my POD HD500X in 4CM. Sorry not able to help more than that. Good luck!