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  • Thinking of buying one of these locally for $175, no cab though as all I've got is combos. Without searching through the previous 45 pages, could I get decent cleans out of this amp if I swapped in some 12AT7's? Looking for a versatile amp with about 15-20W so this seems like a nice option.

    In my opinion the preamp circuit needs addressed (modded) for decent cleans, if you use a Pod/ToneLab etc. it might work to do some tube swapping since most of your tone would come from the floor board. Most EL84 amps aren't known for decent cleans ... it's just way too easy to overdrive an EL84 ... the JCA20H doesn't have decent cleans or clean tone like a Blues Junior, AC-15, Marshall 18 watt etc ...

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    • Thinking of buying one of these locally for $175, no cab though as all I've got is combos. Without searching through the previous 45 pages, could I get decent cleans out of this amp if I swapped in some 12AT7's? Looking for a versatile amp with about 15-20W so this seems like a nice option.

      12at7s ussually dont sound good in MOST preamps. A 12au7 in v2 doesn't give you half bad control over the amount of gain you get with your volume knob.
      Jca 50h/ 100h/ 22h Mod thread and Owners Club
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      • Thanks for the tips, guys. I don't know if this is the amp for me, as I'm honestly not into lots of gain. I know that using a 12AT7 in my 5W combo has given it a good amount of headroom for what it is.
        Looking for anyone in the RI area to jam, practice, etc.
        Good business: colejustesen, theAntihero, dgo ratt, teletaylor, munizfire, stratedge09

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        • Edge11, any more info on the naked mod?

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          • If you wish to increase clean headroom in a tube amp by swapping tubes, you want to reduce the gain of the preamp tubes and increase the gain of the output tubes. The challenge is, you have to find a reputable tube dealer who's willing to test individual tubes, in order to know that what you're buying is going to get you what you want. Buying blindly won't tell you anything.

            Today's tubes are simply far too inconsistent to make any definitive statement on gain, either by brand name or part #. It's not at all uncommon, for instance, to find 12ax7s that test as low as a typical at7, or even lower, in an average 100 lot. So, how can one say that an at7 has lower gain than an ax7, if some of the ax7's in that given hundred lot will test as low, and some even lower than an at7? You can't. Unless you test each tube for gain and conductance, you simply do not know what you're removing or plugging in.

            12at7s and au7s have a different frequency response than ax7s, which is why they're not always seen as favorable swaps. That said, some people like what they hear from them, so there ya are. Tone is subjective, after all, so the only way to know for certain what works for YOU is to try some different things for yourself and judge based upon what you hear/feel. Assuming all tubes of a particular part # were the same value, a 5751 could be seen to have lower gain than a typical 12ax7, yet retains a very similar frequency response, so, assuming you can find reliable gain values for each given tube, the 5751 could generally be seen as a more suitable replacement for a 12ax7, if reduced gain but similar tone is the goal. All of that still relies upon gain testing, however, because without that, you have no clue what you're working with.

            This amp has a pretty large amount of front end gain, and, along with that, suffers from a grainy quality that comes from the stock output transformer. To my ears, it was that grainy quality that made it impossible to get good clean tones from the stock amp, and it also contributes to a pretty inarticulate, sloppy distorted tone as well. Even swapping V1 and V2 and dialing the gain control back won't get rid of all of the fizz in the stock amp, because some of it is that graininess that's coming from the OT. The stock OT simply does not allow the amp to become anywhere near what it's capable of.

            But, again, tone is subjective, and there are clearly many who like the stock amp the way it is. It all comes down to what YOU find inspiring. Others can merely offer their insights, based upon their own personal, subjective tastes in tone. Use those to build your own set of ideals for your own personal, subjective tastes. It's a journey, not a destination.

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            • Quote Originally Posted by Bigmark
              View Post

              Edge11, any more info on the naked mod?




              I haven't had time to research it more but I'm on break after tomorrow.

              We need to find buddah super drive schematics so we can get into friedman's head a little bit.
              Jca 50h/ 100h/ 22h Mod thread and Owners Club
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              • I just returned my JCA20H...VERY FIZZY and the mods are so sketchy on the forums I didn't want to risk it...besides..it started just fizzying out...Thank GOD I didnt' get convinced to spend ANOTHER 250.00 to get a mod that cost as much as the damn amp...besides...my B52 AT100 kicks its ass out and in the door...along with most any marshall out there...

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                • I just returned my JCA20H...VERY FIZZY and the mods are so sketchy on the forums I didn't want to risk it...



                  Good for you. Sounds like you made the right move for yourself.

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                  • Quote Originally Posted by armaddy63
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                    I just returned my JCA20H...VERY FIZZY and the mods are so sketchy on the forums I didn't want to risk it...besides..it started just fizzying out...Thank GOD I didnt' get convinced to spend ANOTHER 250.00 to get a mod that cost as much as the damn amp...besides...my B52 AT100 kicks its ass out and in the door...along with most any marshall out there...




                    Did you change the preamp tubes? And I'm glad you didn't pay 250 dollar for mods. If a tech is using my mods as a guide line he shouldn't charge much at all. So now the question is who wanted to charge you 250$? Sorry that it wasn't the amp for you.
                    Jca 50h/ 100h/ 22h Mod thread and Owners Club
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                    • I found the super drive schematic I'll post it up when I get out of bed tomorrow morning. There's 2/3 interesting things in there about the sd that aren't on the schematic but in the final build.
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                      • The budda schematic



                        So to answer your question big mark it is possible just pretty hard to do and not everything is in the schematic.

                        I'm planning on making the 100/50/22h mod thread soon I might be able to fit a 100 h into my budget in a couple of days.
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                        • Put a Sovteck 12axywa into V1...cleaned -up the crunch channel on my JCA 22 NICELY!
                          Originally Posted by chainsaw fats
                          Can I drink your piss?




                          Great people: d_dave_c, wbcsound.

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                          • Quote Originally Posted by 67mike
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                            Put a Sovteck 12axywa into V1...cleaned -up the crunch channel on my JCA 22 NICELY!




                            What else are you running in it man? and congrats on the buy!
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                            • Quote Originally Posted by Edge11
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                              What else are you running in it man? and congrats on the buy!




                              Thanks, everything else is stock...I bought an Electro Harmonix EL84, because I thought I had another at home....wrong.



                              I plan on putting EH el84s in it, and some jj or rubies in v2 and v5.
                              Originally Posted by chainsaw fats
                              Can I drink your piss?




                              Great people: d_dave_c, wbcsound.

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                              • Quote Originally Posted by 67mike
                                View Post

                                Thanks, everything else is stock...I bought an Electro Harmonix EL84, because I thought I had another at home....wrong.



                                I plan on putting EH el84s in it, and some jj or rubies in v2 and v5.




                                I'd get matched power tubes that way your bias on one tube won't potentially be so Mismatched with the other tube. And as for sovetek tubes in v1 I like going chinese on the next tube just because the sovetek is a really "polite" tube
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