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Marshall jcm800 18W

Posted: Tue 12/23/25 2:34 pm
by MaxKov18
Maybe someone has a good circuit for a marshall jcm800 at 18W. I'm a newbie and I want to make this amplifier.

Re: Marshall jcm800 18W

Posted: Wed 12/24/25 10:31 am
by Crabman
You can buy this kit from Tube-Town:

TT-Kit JC18

Its a JCM-800 preamp with 18watt power section.

Re: Marshall jcm800 18W

Posted: Wed 12/24/25 12:15 pm
by MaxKov18
Thank you very much, I'm a beginner, but I've always dreamed of a Marschall jsm800 2204. However, I need to play at home, so I don't want to use a lot of power.
I saw that there is no fuse switch in this circuit. But I figured out whether it is possible to transmit with one cord to two connectors - switching the desired one using the fuse switch.

Re: Marshall jcm800 18W

Posted: Thu 12/25/25 12:53 am
by Crabman
I guess you could do that, but most folks wouldn't bother with the low sensitivity input since it cuts out the first gain stage. Its an attempt to get a cleaner sound but the 800 is all about pushing 3 gain stages into a cathode follower ...

Keep in mind an 18 watt amp is still very loud running at the sweet spot so you may need to attenuate it somehow for home use.

Re: Marshall jcm800 18W

Posted: Thu 12/25/25 5:33 am
by Bieworm
Maybe look into the JTM1? It’s a 1 watt amp with a 12AU7 PP output stage. It’s remarkably loud as well, but manageable

Re: Marshall jcm800 18W

Posted: Thu 12/25/25 8:14 am
by MaxKov18
thanks, but JTM1 won't work for me because I'm also going to drag an amplifier to the rehearsal base. Right now I'm playing with what's on the base. It's "Dumble OS #124 Clone". - great but not mine and not the overload I need.
I've always liked the sound of "Marschall -jcm800", so I want this sound for myself))
I know that there are "SC20H" and "2525H" - they have the ability to turn on 20 - 5 watts. For practicing at home, that's exactly what I need. But how to make it so that you can switch the strength?
Now, the scheme - "TT-Kit JC18" I like. So I'm collecting information - is it possible to:
- add to the scheme the ability to switch the power from 20-5 watts.
- how to make it so that it can switch through the foot switch to the "LOW" or "HIGH" cascades - I think this can be done with the "A/B box"

Re: Marshall jcm800 18W

Posted: Fri 12/26/25 10:06 am
by MaxKov18

Re: Marshall jcm800 18W

Posted: Sun 12/28/25 4:41 am
by Bieworm
Maybe look at similar online stuff about tis amp?

Re: Marshall jcm800 18W

Posted: Sun 12/28/25 11:58 pm
by Crabman
Not sure how they are going from 20 to 5 watts ... would need to see the schematic. The SC20H uses a pair of EL34s not EL84s like the 18 watt, so I'm guessing that Marshall use a combination of cathode bias and lower plate voltages in the power section to get down to 20 watts? The EL34s are probably operated in triode mode to get the lower power configuration ...