Jca20 Jose Mod Difficult For Beginner?

[Mr.Farva]

Picked up a Jca20 from GC for $200 to try it out, and a 1960B for $238. I remember reading the the Jose/Browneye wasn't to hard to do? Are their any tutorials, schematics, parts list etc.?



http://mrfarva.imgur.com/all/" onclick="window.open(this.href);return false;

[mightymike]

Nice score.
Here's a schematic I found that shows what to change to make your amp Jose spec..I was just looking at this earlier today. It showed up in google images when I was searching for Jose High Gain Mod.. Lucky you
NOTE: V2 is mislabled as V1. V1 is on the left. Also, notice on the schematic the big brown dots highlighting changed values, and no label next to added values like the 100k and 470pf added to v1a plate in step 1 for example.

This isn't too difficult for a beginner imo. Just follow safety procedures, Uplug the amp, and drain your caps before working on it so you don't kill yourself. If you don't know how.. Just ask, or hire a pro.
$10 to $20 in parts, and 30 minutes to perform the changes.

Here's a quick parts list and instructions I made up to help.

Parts list:

3) 470pf
100k ( or 330k)**
.68uf
2) 68k
470k

Instructions:

Step1)
Add 100k in series with r28 220k and then put a 470pf across it ( or replace 220k r28 with 330k and put the 470pf across that instead)**

Step2)
Add .68uf across the 2.7k r25
(Wow it's not already there. It's like a 2204 with a 2.7k instead of a 10k interesting)

Step3)
Add 68k from v1 pin 2 to in between r53 and vr6*

Step4) Jump r32

Step5)Remove c23

Step6) Cut trace between r36 and c23

Step7) Add 470k from r36 to ground and add 470pf across it

Step 8 )add 470pf across r36

Step9)Replace r33 with 1m pot that used to be vr6

Step 10) Optional 33k r21 slope resister.

*vr6 used to be a 1m pot, now is a 68k. Vr6 is moved to replace r33.. Not moved from where it's mounted, just how it's connected to match the edited schematic.

Have fun

[mightymike]

After all that I found the source....
http://www.harmonycentral.com/t5/Amps/J ... p/28031120" onclick="window.open(this.href);return false;

[Mr.Farva]

Thank you! Still debating if I'm going to attempt this mod or just return the amp... Can I order the parts from valve storm, or just go to radio shack? I would also like to add a SAT switch. Assuming I'll have to pull the board out of the chassis? Also wondering how I drain the amp. A double ended alligator clip wire?

[mightymike]

Yes Valvestorm

I don't think you will have to take put the PCB... All the parts look accessable from your pic. Remember you're not actually moving the pot, just the trace

Yes a clip wire from v1a plate to ground. (That's wbere the 220k in step1 is) I like putting a nice power resister on the wire to eliminate popping. There's a thread here on draining caps if you do a search.

[Mr.Farva]

So I turned it on today and noticed a sound, sounded like I was wigging my guitar cable. Looked at the back and saw one of the power tubes glowing red. Only does it off standby. Swapped tubes and it does it in the same socket. Pulled the chassis checked all of the solder joints, none of them wiggled. Any ideas? Theirs no fuse on the back of the amp?

[bobtec]

[Lefty Lou]

This is a good thread for you:

http://forum.metroamp.com/viewtopic.php ... 6&start=15" onclick="window.open(this.href);return false;

AND

http://forum.metroamp.com/viewtopic.php?f=10&t=31746" onclick="window.open(this.href);return false;