Guitar Gear Forum

This thread is intended for photos, schematics, manuals, and other reference materials for the JCA50H only. Lots more info in the JCA Owner's Thread

Preamp section



Power section

Power





Output:




Choke:


Mounting:

Schematic corrections:

Pins 1 and 6 are missed numbered on the preamp schematic. reverse 1 and 6 for V1 V2 V3 and V4
Correction The schematic above is correct I have a copy with the same date drawn incorrectly from the thread on HCA forum.
Check R35 and R36. I have 220k for R35 and 470k for R36These values are correct from the factory-see post below
The 6.3 VAC secondary has a center tap not shown
There is no V6 V9 or pilot lamp connected to the 6.3 VAC secondary (older amps with the toggle switches do have a pilot lamp)
There is a 12 VAC secondary not shown on the PT. They just show the AC12v magically appearing
There is a connection shown as VCC in the relay circuit. It connects to the foot switch circuit shown in the lower right hand corner of the schemo. Maybe they intended to have a front panel switch and left it out in production?

Power supply voltages @120VAC input no tubes

OT center tap 508 VDC
Raw bias tap 63.7 VAC
Filament supply 6.73 VAC
12 volt tap 12.39 VAC
HV secondary 740 VAC

Very interesting - thanks for the input. I've actually seen at least one other schematic that was similar, but different enough from what I was actually seeing on my particular head, that I decided to stay with this one, which was closer. I do seem to recall some differences, regardless - when I get a chance, I'll break open my chassis and verify what I've witnessed, as well as what you've stated here.

This is good stuff!

as per Doug @JCA the R35\36 values posted above are correct from the factory. He describes it as a running change after launch.

What is the tube layout for the JCA50? I have the JCA5012C combo. Thanks.

frankencat wrote:What is the tube layout for the JCA50? I have the JCA5012C combo. Thanks.

V1 to V5 (small tubes) all in a row. V1 is nearest input jack. Power tubes are the big ones.

Hello,

do you know the maximum current capability of the 12V winding. Would like to add two additional relays (each draws ca. 12mA) and dwo diodes (each 10mA) which requires additional 45-50mA. Would it be possible with the standard PT in JCA50H?

I could have sworn I heard specs on that at some point, but damned if I can remember. I'd suggest emailing Doug @ JCA and see what he says. He's been entirely helpful in the past. Please post what you find, though

Hello,

first of all- Doug is one of the most supportive people I had a chance to talk to/mail with! Based on this I do wish everything best to JCA

And here are the details of the PT secondary for JCA50H:
6,3V - 5A (blue- blue)
11,5V- 0,8A (brn-brn)
350V- 0,25A (rd-blk)x2
58V- 0,2A (blk- wht)

Great! Glad it worked out, and thanks for contributing to the knowledge base!

Very interested to hear how your modding goes

My mods are "standard" (clean with C28 disconnected for clean, connected for crunch + SLO mod) but I wanted to have foot-switchable clean/crunch and LEDs for clen/crunch and cruch/OD as I already drilled front panel (at the moment I wired clean/crunch and "bright" on DPDT switches) so would like to populate those "holes". Will post a schematic on "moding" thread maybe with some pics