Amps

[Mark_McQ]

Should I be putting a cap in line if I wire a pot in series with the slope resistor?

[Edge11]

Originally Posted by Seattle Doug

Yep, pretty much. Joe has and uses a 20H all the time (you can see it in all kinds of photos of his live rig). His tech told me Joe was looking for a bit less gain and more 'vintage' feel, and a little darker. So that's what we did. Joe did NOT care about the depth switch nor the effects loop (doesn't use them), but those were features we thought would make the amp a little more different than 'just another 20H with a different voice'. So when we got the first production unit in, after we tested it we gave it to Joe, and he used it on a LOT of the new Aerosmith record. The stock 20H he has relegated to be specifically his talkbox amp, that's why you see a little 20 watter among all his more powerful amps in the rig.

DIY kit - dang... I need to get back on that...

True that.
Also a three channel all tube preamp would be sweet as well.

Originally Posted by Mark_McQ

Should I be putting a cap in line if I wire a pot in series with the slope resistor?

Wait what?
Cap in line with what?

[MR MARCUS]

Is there any way to add diode clipping to the existing gain knob?

[chimaira66]

Originally Posted by Edge11

I'm considering opening a seasonal mod shop to do mods during winter break. Who's interested?

I am for sure...

[chimaira66]

So let me get this straight, I simply get a 1 meg pot and the capacitor of that value, connect one side to resistor and one side to +speaker out off of the board? and drill a hole in the chassis for the pot and that's it? (for depth mod)

[Edge11]

Originally Posted by chimaira66

So let me get this straight, I simply get a 1 meg pot and the capacitor of that value, connect one side to resistor and one side to +speaker out off of the board? and drill a hole in the chassis for the pot and that's it? (for depth mod)

I have 2 more weeks of school left I'll send you a pm when my body is ready.
You literally just drill a hole cut the feedback wire in 2 and put the depth circuit in there.
http://home.comcast.net/~jbjdav26/Resonance2.JPG

[Mark_McQ]

Originally Posted by Edge11

Wait what?
Cap in line with what?

It's ok, had mistook something I read. All sorted now.

[IBDBB]

is there a list of mods in a simple list format as opposed to the schematics?

I have a hard time reading those things.

as in:

change R1 to 330k
change C4 to .022
remove c21

etc....

i'd love to try the vh4 mods.
I may have a chance to get one for 150 used.
i modded my v33h a year or so ago with dvnators mods and it sounds great and was very easy
thanks

[Edge11]

Originally Posted by IBDBB

is there a list of mods in a simple list format as opposed to the schematics?

I have a hard time reading those things.

as in:

change R1 to 330k
change C4 to .022
remove c21

etc....

i'd love to try the vh4 mods.
I may have a chance to get one for 150 used.
i modded my v33h a year or so ago with dvnators mods and it sounds great and was very easy
thanks

Yes read the first post on the first page

[IBDBB]

Originally Posted by Edge11

Yes read the first post on the first page

yes, thank you, don't know how i missed that... YOur mods are very easy to read and seem pretty easy.

Would you care to list out the dues/vh4 mods?

[Edge11]

Originally Posted by IBDBB

yes, thank you, don't know how i missed that... YOur mods are very easy to read and seem pretty easy.

Would you care to list out the dues/vh4 mods?

Then you would never be able to learn to read a schematic. It's easy, I believe in you.

[macheted01]

Hey All,
I've had my eye on one of these, since the day they came out. Currently, one of my band members is an amp and guitar tech and will be doing any work that I need done. The only other tube amp that I have owned was my Ampeg V2 and matching 4x12, which I recently sold. It was just too much and too big.
I am thinking I will just upgrade the tubes. Would also like to consider putting in an effects loop. After reading through this thread a bit, I was wondering what you guys decided that may have been the best choice to do so? I seen the Zero Loss FX Loop kit from Metroamp and one other choice on this thread, so far. I have not completely made it through the whole thread yet. As I said, I have a guy to do the work, I would just like to grab as much info ahead of time, as I can.
I know there is the JCA22H and also the JCA20HV that is out now, but at that price point, I would maybe consider a different amp all together. If I was gonna go that far, I was thinking, I might as well throw another $200.00 in and go for something like the Hughes & Kettner Tubemeister 18, unless I am missing something here.
I just like the price point that I can get into the JCA20H for and get the work done for free other than parts. He may even have a different approach other than what is listed, I dont know. Looking forward to hearing your thoughts.

[stilllifer]

Originally Posted by macheted01

Hey All,
I've had my eye on one of these, since the day they came out. Currently, one of my band members is an amp and guitar tech and will be doing any work that I need done. The only other tube amp that I have owned was my Ampeg V2 and matching 4x12, which I recently sold. It was just too much and too big.
I am thinking I will just upgrade the tubes. Would also like to consider putting in an effects loop. After reading through this thread a bit, I was wondering what you guys decided that may have been the best choice to do so? I seen the Zero Loss FX Loop kit from Metroamp and one other choice on this thread, so far. I have not completely made it through the whole thread yet. As I said, I have a guy to do the work, I would just like to grab as much info ahead of time, as I can.
I know there is the JCA22H and also the JCA20HV that is out now, but at that price point, I would maybe consider a different amp all together. If I was gonna go that far, I was thinking, I might as well throw another $200.00 in and go for something like the Hughes & Kettner Tubemeister 18, unless I am missing something here.
I just like the price point that I can get into the JCA20H for and get the work done for free other than parts. He may even have a different approach other than what is listed, I dont know. Looking forward to hearing your thoughts.

Hey. Well since this is a JCA20H Mod thread, we are possibly a tad biased!!! Regardless, I don't think you can go wrong with the JCA20H or 22H, especially since you can get the mods done for nothing - best price of all!!! The Tubemeister is pretty cool, especially with its' built in power soak and DI for recording but honestly, I found it was just OK, even cranked into a 4x12 - found it very loose sounding (could be stock tubes, no mods etc) but wasn't blown away. I think my JCA20H is way better, actually slays the H&K - much tighter sounding even before any mods done. You will def want to swap out the tubes IMO (some guys like the stock tubes, YMMV) but I hated them. I put in vintage Mullard EL-84's and various 12AX7's and 7025 and it is an amazing difference in tone. The mods on first couple of pages of this thread are great - the Super Sucker Punch and Depth mods I've done have made a world of difference. I now run this head with the preamp gain down just to breakup into my Carl Martin Plexitone pedal and I've got Marshall tones from JMP to full-out JCM800 into my 2x12. You won't regret it man!

Cheers! Geoff

[macheted01]

Thanks Geoff for the reassurance, because I just bought a JCA20H through ebay for $203.00 with shipping. No mods done, just re-tubed with JJ EL84 (2) power tubes and JJ 83S (3) preamp tubes. Cant wait to get it. When it gets here, I will decide where I need to go with. Pretty sure I will be looking to put in the FX Loop. For those here with experience with the Loop, i was wondering what the best approach was.
Currently using my backup amp to the Ampeg V2, which is a Crate Powerblock. Soon to be my backup to the JCA20H, if things work out as planned. I used to dump my effect chain straight in to the front of my V2, but really found it lacking for the obvious effects. With my Powerblock having an FX Loop, proves to be a big improvement. So, in any case, I am leaning towards getting the loop in first.

[Jead72]

YIKES! Not really a mod question but a cry for HELP! I have 2 jca20h's #1 I did the depth mod and added a choke to. #2 I just got and it seemed to be working fine (besides the intermittent blue power led). I did the depth mod for it using a 250k cts audio pot instead of a 500k. I started the amp up and the volume was maybe about 1/4 to 1/3 of what it should have been and then after a few minutes it kicked in to where it should be. It then, accompanied by a bit of static, went back to 1/4 or 1/3 volume. I could tell that the depth was working. I have known good tubes.

I'm at a loss as to what has happened. I went and undid the mod and had the same lack of output, re-soldered the mod back in and - same. I'm not afraid to troubleshoot the amp but I really have no idea where to begin with it. I fear I may have a sketchy OT. Can anyone lend their thoughts and experience?
Currently bummed out,
Jay

ps: the output is really broken up and staticy and seems to have something of an oscillation quality. Sounds like the gain is way up when it's not. Every once in a while the static disappears but no further change.......

[Edge11]

possible bad tubes, (recheck them if you can) bad solder joints, broken pots you name it. look for visual signs, then whip out the v meter. I'll post up a good debugging workflow when i get up in the afternoon.

[Jead72]

Issue solved. As it turns out there must have been a fair amount of solder on the 8 ohm output I soldered the NFB from the resonance pot to. All I did was reheat the tab and add the wire but a blob somehow managed to bridge the contacts below where I was working so it was really difficult to spot. An easy fix but really irritating to find. Now if I could only eliminate the hum on these amps I'd be happy. Why no DC filament??? I have a couple mini hum balance pots and it looks like if I stuck them in with r10 and r11 and got a ground somewhere, that might help. Not exactly sure on that but it seems a reasonable idea. Any thoughts on that or other ways to reduce the hum?

[macheted01]

Alright, I have my JCA20H and loving it. I might go for a little more clean headroom, but I still am more interested in the FX Loop. Have not heard back from anybody on it. Would like to know what the best approach for the loop was? Thanks.

[Jead72]

I built a couple enclosures for the kids.

[IMG]http://i250.photobucket.com/albums/gg270/Jead72/2013-01-19001.jpg[/IMG]

[IMG]http://i250.photobucket.com/albums/gg270/Jead72/2013-01-19002.jpg[/IMG]

[IMG]http://i250.photobucket.com/albums/gg270/Jead72/2013-01-19005.jpg[/IMG]

[Edge11]

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Jead72 wrote:

I built a couple enclosures for the kids.

[IMG]http://i250.photobucket.com/albums/gg270/Jead72/2013-01-19001.jpg[/IMG]

[IMG]http://i250.photobucket.com/albums/gg270/Jead72/2013-01-19002.jpg[/IMG]

[IMG]http://i250.photobucket.com/albums/gg270/Jead72/2013-01-19005.jpg[/IMG]

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can't see any of those, stupid forum update!

Plugged them in manually and they look great, very vintage!