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Edge11

Jca20H Mod thread and owners club.

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The Jca 20h Owners Club and Mod Thread
Yes I do custom mods/parts lists/Mod other amps, pm me for more info/pricing.
The purpose of this thread is going to be for discussing Mods to the jet city 20H, or any other topic pertaining to the JCA model 20H.
The stock 20h
The stock 20h is a 2 el84, 3 12ax7 amp featuring a soldano slo Treble, Middle, Bass tone stack with a Presence control in the Power Amp. Two 8 ohm output taps and one 16 ohm output tap. Excellent price for an amp with no unneeded frills.
Sound Clips
Guitar World

A Real owner

Stock Schematic
YFMWC.jpg
High Voltage Warning
WARNING! - Please Read this Information Carefully:
The projects described in these pages utilize POTENTIALLY FATAL HIGH VOLTAGES. If you are in any way unfamiliar with high voltage circuits or are uncomfortable working around high voltages, PLEASE DO NOT RISK YOUR LIFE BY BUILDING THEM. Seek help from a competent technician before building any unfamiliar electronics circuit. While efforts are made to ensure accuracy of these circuits, no guarantee is provided, of any kind!
USE AT YOUR OWN RISK: THE WEBMASTER, PROJECT COORDINATOR, PROJECT CONTRIBUTORS AND WEB SPACE PROVIDER EXPRESSLY DISCLAIM ALL LIABILITY FOR INJURY OR PROPERTY DAMAGE RESULTING FROM THIS INFORMATION! ALL INFORMATION IS PROVIDED

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Other Mods
Dues'(or should I say vh4's now?) mods
Pending permission from duese i think that i can post his schematic in this thread, for now I'll post a link to his thread. His mod were the bassis for my mods (minus the "voicing switch", thats mine).His mods are
Choke,depth, Channel switch (with pot or switches to controll the gain), an effects loop(no he will not give away the schematic to it), a master for each channel, a "global master and various resistor and capacitor differences.
Here is the link to his topic with the schematic to his mods on page 3
http://acapella.harmony-central.com/...-for-299/page3
This is dues's schematic
attachment.php?attachmentid=312810&d=126
All credit for this goes to dues (VH4 here on the forum)
Here is a brief explanation and discussion of the depth pot.
http://acapella.harmony-central.com/...uctions-please
Sound Clips
Les Paul
http://www.youtube.com/watch?v=hchMfnL3BJo
Strat
http://www.youtube.com/watch?v=tdBn83FQYAE
Dave Friedman's mods
Dave friedman of Rack Systems Inc. is offering his "Brown eye" mod for the jca 20H. I seem to recall it costing about 300$ and an additional 50$ for a "saturation" switch (a Jose master volume).
Sound Clips

Depth Mod
This mod is depicted in dues' mod.
Quote Originally Posted by ledvedder View Post
I guess it doesn't matter where the wires go on the pot? VH4's instruction says to solder the 4n7 cap to the left and middle pins of the pot. You have the 4n7 cap to the left and right pins.
Works both ways
This is how I wire it
Resonance1.jpg
how duese wires it
Resonance2.JPG
an here's an extra little diagram to help those who are more visually inclined.
15xlikm.jpg
I have no clue who some people are removing the nfb wire from the pcb and making more trouble for themselves.

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I haven't done any mods myself to mine, but I just got mine back from Dave Friedman today with the brown eye mod and a saturation switch. It sounds killer. Depending on the difficulty, I am interested in possibly adding an FX loop to mine down the road, but I don't know how do-able that would be for a noob like myself

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Quote Originally Posted by spawnofthesith

View Post

I haven't done any mods myself to mine, but I just got mine back from Dave Friedman today with the brown eye mod and a saturation switch. It sounds killer. Depending on the difficulty, I am interested in possibly adding an FX loop to mine down the road, but I don't know how do-able that would be for a noob like myself

 

Thats a very asked for mod, All thought it doesnt appeal to me personaly, I am willing to investigate. With a schem and soldering iron (and some soldering know how) it should be very doable. Hey you dont mind if I put your friedman modded video on here as a sound clip right?

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Oh ya let the games begin. I originally got a JCA50H and it was a lemon and the guys at JCA were great and getting to taken care of. In the mean while I bought a JCA20H from Music123 new for $209.00 Killer. It gets here Tuesday the 6th. My tubes have already arrived.
2-JJEL84
2-JJ12ax7 standard
1-JJ12AX7 balanced
1-JJ12AT7 standard
1-JJ12AX7 HighGain
1-TungSol 12AX7
1-EH 12AX7

Going to mess with that for a minute and soon as I can find a Series Loop mod I am modd'ing

Thanks for starting the thread I hope that this takes off so an arm and a leg is not spent for mods and you can learn something. I love DIY. Amp to this point are really the only thing that I have yet to touch.....I can't wait..

Did you post on the JCA FB page?

theDogger

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Quote Originally Posted by theDogger View Post
Oh ya let the games begin. I originally got a JCA50H and it was a lemon and the guys at JCA were great and getting to taken care of. In the mean while I bought a JCA20H from Music123 new for $209.00 Killer. It gets here Tuesday the 6th. My tubes have already arrived.
2-JJEL84
2-JJ12ax7 standard
1-JJ12AX7 balanced
1-JJ12AT7 standard
1-JJ12AX7 HighGain
1-TungSol 12AX7
1-EH 12AX7

Going to mess with that for a minute and soon as I can find a Series Loops mod I am modd'ing

Thanks for starting the thread I hope that this takes off so an arm and a leg is not spent for mods and you can learn something. I love DIY. Amp to this point are really the only thing that I have yet to touch.....I can't wait..

Did you post on the JCA FB page?

theDogger
I should post on their face book.
What im running in mine that I thought sounds best is a jj long plate in v1 a sovtek russian tube in v2 and the chinese sino in v3.
Edit:I just posted it on their facebook......only to realize that some one beat me to the punch.......

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Quote Originally Posted by jet city amps View Post
Good morning! I will try to check here occassionally and offer assistance when I can...
lol Hey Doug is it alright if I post the official schematic on this here?
Thanks for supporting man.

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OK guys considering making a section dedicated to cosmetic mods (baffles + other things that people have done, like leds).

Quote Originally Posted by Yarbicus View Post
So in! I want to know how different tubes affect the JCA20H.
I'll try to add a tubes tasting section if i can get more people to give some feed back on what tubes they have tried and where. Dogger give us a full report after you get yours.

Quote Originally Posted by jet city amps View Post
I prefer to give the schematic to customers who buy the amp. that seems fair to me, but, what did you have in mind?
Ok, Doug, I'll respect your decision and not post the schematic on here, all though I think it would be a resource to have in this thread. Can you fill me in on the baffles situation (what is offered)? Also need info on the "jet packs" if you guys are even considering doing those any more.

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Just got my JCA20H today and thought I'd post some pics...little worried about the amp as it looks as if MUSIC123 sent me a used amp by the looks of the box and old shipping label..

jcabox.jpg

jcatop.jpg

jcaback.jpg

jcaboard.jpg

jcaboard1.jpg

jcaboard2.jpg

jcaboard3.jpg

jcaboard4.jpg

jcaboard5.jpg

jcaboard6.jpg


theDogger

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Here are some pics of the tube replacement. I love Hi-Res pics. I think that is the best way for thread like this not the photo camera's..that you can't see anything....The stock tube were biased cold 16.6ma. I swapped them out with some JJ's from www.EuroTubes.com They are great! I got the following tubes and will try and do a run down as soon as I can figure out how to get a decent recording..
2-JJ-EL84
2-JJ-12AX7 Standard (V1 & V2)
1-JJ-12AX7 Balanced (V3)
1-JJ-12AX7 HighGain (V1)
1-JJ-12AT7 Low Gain (V2)
1-Tungsol 12AX7 Standard (V1 & V2)

I measured the Voltage at pin#7. It read 362. So I biased it @70%.
11.5/362*.70=.021875 so I set the bias @ 21ma

So I set it at 21ma. The JJ's quieted the noise a little, made it darker but in a good way. With the master set at 3 and the pre at 1 it was sounding like it wanted to break up so I swapped the V2 with the 12AT7 and tried it again and it was clean up to about 3 now before it sounded like it wanted to breakup.

So fo now I have settled for the all standard JJ until I get use to the amp and can mess w/it more.

jcajj2.jpg

jcajj.jpg

jcabias.jpg

jcabias3.jpg

theDogger

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Quote Originally Posted by theDogger View Post
Here are some pics of the tube replacement. I love Hi-Res pics. I think that is the best way for thread like this not the photo camera's..that you can't see anything....The stock tube were biased cold 16.6ma. I swapped them out with some JJ's from www.EuroTubes.com They are great! I got the following tubes and will try and do a run down as soon as I can figure out how to get a decent recording..
2-JJ-EL84
2-JJ-12AX7 Standard (V1 & V2)
1-JJ-12AX7 Balanced (V3)
1-JJ-12AX7 HighGain (V1)
1-JJ-12AT7 Low Gain (V2)
1-Tungsol 12AX7 Standard (V1 & V2)

I measured the Voltage at pin#7. It read 362. So I biased it @70%.
11.5/362*.70=.021875 so I set the bias @ 21ma

So I set it at 21ma. The JJ's quieted the noise a little, made it darker but in a good way. With the master set at 3 and the pre at 1 it was sounding like it wanted to break up so I swapped the V2 with the 12AT7 and tried it again and it was clean up to about 3 now before it sounded like it wanted to breakup.

So fo now I have settled for the all standard JJ until I get use to the amp and can mess w/it more.

jcajj2.jpg

jcajj.jpg

jcabias.jpg

jcabias3.jpg

theDogger
Can't wait to hear since we're using a similar tube compliment.

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Quote Originally Posted by theDogger View Post

I measured the Voltage at pin#7. It read 362. So I biased it @70%.
11.5/362*.70=.021875 so I set the bias @ 21ma
I have the same tube replacement from eurotubes, but I am ordering my bias probe today so I haven't biased it yet. It just took me a couple weeks before I felt comfortable biasing my own amp. The way you figured out the bias, and the way I did are a little different. I use 12 watts dissipation, instead of 11.5. So... my amp is running at 360 plate voltage. I would do 12/360=.033 *.7= .023 milliamps. I double checked this with the weber bias calculator on their website and the numbers come out right. The link for the weber bias calculator is:

http://www.webervst.com/tubes1/calcbias.htm

I'm not trying to tell you you're wrong, it's just a sincere question and pursuit of tone.

I will post some pics... but there is a pretty big mar on one of the big traces on the pcb. I don't think it is changing the sound of the amp.... it just doesn't look as pretty inside. I'm hoping I can get a second opinion.

Even without the bias, the amp sounds way better with the JJ's. The gain is much more defined, and the amp is overall a lot more clear and punchy. I imagine that my power tubes are only running about 50% as well... and I am excited to hear what they sound like at 70%

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i too am using JJs.

im using high gain 12ax7s, and balanced HG JJ in the PI slot, and 2 early breakup JJ el84s.

very happy with the change in tone, clean and dirty.

i wonder how much adding reverb would cost... smile.gif

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Quote Originally Posted by guitarmadman85 View Post
I have the same tube replacement from eurotubes, but I am ordering my bias probe today so I haven't biased it yet. It just took me a couple weeks before I felt comfortable biasing my own amp. The way you figured out the bias, and the way I did are a little different. I use 12 watts dissipation, instead of 11.5. So... my amp is running at 360 plate voltage. I would do 12/360=.033 *.7= .023 milliamps. I double checked this with the weber bias calculator on their website and the numbers come out right. The link for the weber bias calculator is:

http://www.webervst.com/tubes1/calcbias.htm

I'm not trying to tell you you're wrong, it's just a sincere question and pursuit of tone.

I will post some pics... but there is a pretty big mar on one of the big traces on the pcb. I don't think it is changing the sound of the amp.... it just doesn't look as pretty inside. I'm hoping I can get a second opinion.

Even without the bias, the amp sounds way better with the JJ's. The gain is much more defined, and the amp is overall a lot more clear and punchy. I imagine that my power tubes are only running about 50% as well... and I am excited to hear what they sound like at 70%
That is not a huge issue. You can use 11.5 or 12 watts. the difference between 21ma and 23ma is not a big deal. If it was 16ma and 23ma then there would be a difference. A lot of guy think that 70% is too high and that 60-65% should be used.

I just ordered the BitMo Surfa mod.........

FYI - I am returning my amp to MUSIC123 for a replacement. They sent me a used amp that had an issue with the blue Power Light. Why do I say it is a used amp? Because there is a shipping label under my UPS label for a different party in Indiana. So I paid for a new JCA20H and got a returned open box with a power light issue...Called MUSIC123 an they have issue an RMA.
This is the 2nd time that it has happened to me...the other time to was from SamAsh with a Bugera 6262.

Really kinda pisses you off!

theDogger

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I just ordered a few JJ's myself. 2 - EL84's, 1 - ECC803s (hi-gain), 1 - ECC83s (Hi-gain) and then I orderd a balanced Sovtek LPS and a Electro-Harmonix 12ax7EH. But, I can't play with them until I get home from a business trip on Friday cry.gif

I'm still probably going to try some regular gain JJ ecc83s too, depends on what I think of the hi-gainers. I had heard that regular JJ ECC83s' are a lower gain tube, which is why I went with the hi-gain version.

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Quote Originally Posted by theDogger View Post
That is not a huge issue. You can use 11.5 or 12 watts. the difference between 21ma and 23ma is not a big deal. If it was 16ma and 23ma then there would be a difference. A lot of guy think that 70% is too high and that 60-65% should be used.

I just ordered the BitMo Surfa mod.........

FYI - I am returning my amp to MUSIC123. They sent me a used amp that had an issue with the blue Power Light. Why do I say it is a used amp? Because there is a shipping label under my UPS label for a different party in Indiana. So I paid for a new JCA20H and got a returned open box with a power light issue...Called MUSIC123 an they have issue an RMA.
This is the 2nd time that it has happened to me...the other time to was from SamAsh.

Really kinda pisses you off!

theDogger
Forget Music123, Musicians Friend, etc.... Sweetwater is the only place that I will spend my money for new gear these days. Those other dealers hire monkeys for employees (no offense to anyone on here that works at either icon_lol.gif)

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Quote Originally Posted by Kidbs

View Post

Forget Music123, Musicians Friend, etc.... Sweetwater is the only place that I will spend my money for new gear these days. Those other dealers hire monkeys for employees (no offense to anyone on here that works at either icon_lol.gif)

 

I used to work for them. You are correct.

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Quote Originally Posted by theDogger

View Post

That is not a huge issue. You can use 11.5 or 12 watts. the difference between 21ma and 23ma is not a big deal. If it was 16ma and 23ma then there would be a difference. A lot of guy think that 70% is too high and that 60-65% should be used.

 

Cool. I just wanted to make sure I wasn't doing my calculations wrong. I would be interested to hear your opinion on how much the bias helped the amp. I understand that they are biased a little cold from the factory.

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