JCA50H Documentation

[Tortuga]

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

[Tortuga]

Preamp section



Power section

[Tortuga]

Power





Output:




Choke:


Mounting:

[ironman28]

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

[Tortuga]

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!

[ironman28]

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

[frankencat]

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

[Tortuga]

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.

[autko]

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?

[Tortuga]

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

[autko]

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)

[Tortuga]

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

Very interested to hear how your modding goes

[autko]

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