Page 1 of 1
JCA22 ClassicTone Output Transformer and Mods
Posted: Fri Mar 11, 2016 5:16 pm
by TTBull
...
Re: JCA22 ClassicTone Output Transformer
Posted: Fri Mar 11, 2016 5:26 pm
by Tortuga
Hey - that's great info!
I'll add this to the references section on my JCA thread - make sure you check it out when you get a chance. See my signature for the link.
Re: JCA22 ClassicTone Output Transformer
Posted: Fri Mar 11, 2016 5:32 pm
by Tortuga
Done!
Re: JCA22 ClassicTone Output Transformer
Posted: Fri Mar 11, 2016 7:47 pm
by TTBull
...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Sat Mar 12, 2016 6:12 pm
by TTBull
...
Re: JCA22 ClassicTone Output Transformer
Posted: Sun Apr 03, 2016 5:22 pm
by Meelocheck
TTBull wrote:Here's another interesting Mod.
Im sure everyone has....at some time replaced R6 the Stock 220k Plate Resistor with a 100k Resistor.
Reason being the 100k resistor gives a very open sounding tone, which is a really good thing over all....however the bass frequencies sound terrible like this and tend to become flabby and hard to deal with over all....the amp looses its punch as well.
the above mod is quite simple....it basically places 2x 220k resistors in parallel with each other giving you a final plate resistance of 110k.
However the 2.2n capacitor in the circuit causes the bass frequencies to remain compressed as if the stock 220k resistor is still in place.
so the outcome is simple....it gives you the same open sounding tone as the 100k resistor does....but now the bass is tight sounding being its still compressed....holds together even better, and allows the amp to remain punchy...gives better control over the bass and depth pots as well. any type of palm muting is much easier to do as well.
i highly recommend this mod...works for the jca20/22/50/100.....or ANY tube amp that has a very...open flabby sounding bass.
make sure the 2.2n capacitor is rated at atleast 400v
Thanks for this. Will def look into giving it a go. I've done the Depth mod and messed around with a few different resistor values here and there. I put c6 on a switch as well. I can't recall what I left the plate resistor at...The problem I am having is exactly as you described though so hopefully this will help deflub the bottom end a bit.
After digging around it looks like I have a 4.7nf 500v cap on hand, no 2.2nf...Is that an acceptable substitution for 2.2nf and what would the difference be?
Again, thanks.
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Mon Apr 04, 2016 3:34 am
by TTBull
...
Re: JCA22 ClassicTone Output Transformer
Posted: Mon Apr 04, 2016 4:57 pm
by TTBull
...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Tue Apr 05, 2016 4:59 am
by Zozobra
6K6 primary? I'd have thought for EL84s at @340VDC 8K would have been more suitable?
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Tue Apr 05, 2016 6:06 am
by TTBull
...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Tue Apr 05, 2016 6:34 am
by Zozobra
I would have though that the load line would be pretty abusive at 6k6 and the EL84s are already stretched over the limiting values at 340VDC!
If it works it works I suppose but I guess it would chew up tubes pretty quickly. I never understood why they didn't use 6V6s in this amp...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Tue Apr 05, 2016 6:50 am
by TTBull
...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Sat Apr 09, 2016 10:57 am
by Meelocheck
I couldn't totally remember what I did and undid the last time I had this sucker opened up...Now that I opened it up again I see I left R26 at 220k. I added another to make it 110k. I then did that compression mod on R6 using the 4.7nF cap I had and a 220k resistor. I dunno what it did exactly, but it opened the amp up a ton. Last time I changed R6 back to 220k from 100k as it lost a little bit of bite - less harmonics, not so edgy. This way, with the cap in the circuit it makes a huge difference. The switch I added for C6 definitely became more usable as the audible difference between on and off is much greater. Totally digging this...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Mon Apr 11, 2016 9:55 pm
by TTBull
...
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Mon Apr 11, 2016 11:28 pm
by Tortuga
That's pretty cool - does it work in the preamp or power section? More effective than a pedal noise gate?
Re: JCA22 ClassicTone Output Transformer and Mods
Posted: Tue Apr 12, 2016 12:02 am
by TTBull
...