18Watt.com

Hello folks, this is my first post here but what a great site!
I recently salvaged this old amp from the trash and was able to get it working properly, but I have no idea what this circuit is similar to! I've built a couple champ 5f1's but thats about it. Its obviosly been modified [a long time ago] as it was drilled for two more preamp tubes and one more pot. Theres also a section of the pcb that is no longer wired to anything. This appears to be some East German 70's 2xEl84 TMB amp [Tesla potentiometers,Bohm mains transformer], and sounds pretty decent! I had to replace all the electrolytics [and drill bigger holes for the two 50uf+50uf can caps. Put a new choke in, new EL84 sockets, Cliff jacks and new speaker jack and a few 3w resistors. I've never seen an amp use two 50uf + 50uf power caps and two cathode bias resistors in parallel, but again I'm only really familiar with tweed champs/princetons. I'd appreciate it if anybody has time to glance at the photos and give me your estimation of whats going on.

ok....I'll try again

Do you have more background about this amp? The high filtration value brings it more into plexi or even bass amp territory. It’s odd in a dual EL84 configuration. Doesn’t it sound a bit stiff like that?

Thanks for the reply!
It sounds pretty clean, maybe a bit stiff but I'm enjoying the clean tones. Not noisy and a good pedal-platform.All the eq knobs are very responsive and do what they should. Unfortunatley I know nothing about its origin and there are no markings anywhere to hint at who made it. It was left out by the trash with no cabinet, just the chassis.
I'm really happy its alive and that the transformers were all good.
I've never seen any of these capacitors before. The two big can caps were strange 50uf+50uf pink Tesla caps and they were pretty dead. I'm in the Czech Republic and it looks like an East German late 70's design. Vermona,Regent,Tesla etc?
Just wondering if the layout/circuit looks at all familiar to anyone here as it's a mystery to me. Its a cathode biased 2xEL84 amp....that's all I got!

Did some tidying up, [new tube sockets/heater wires and other things]. The amp sounds wonderfull but is definately designed for clean headroom, which is perfect for my use and the type of music I play. [R&B/Reggae/Rockabilly/blues]
I'd still like to know whats going on with some of the values/parts choices but heck 'if it ain't broke don't try to fix it!' I re-housed it in an old Randall RG30 cab I had in the closet, the Randall knobs kind of complete the look. And to enhance its stellar clean-tones I installed an old JBL D123.
This amp was never going to be a rocker, so I embraced it's clean-tone strength and it's a keeper!

[

We could discuss it further if you provide a schematic for the build. If you don't already have one, it shouldn't be too hard to draw one on a simple circuit like that.

I don't know why you have 50uF caps in there.

But, if it sounds good to you, enjoy it.

Thanks,
Josh

Any chance of uploading the images to somewhere other than Imagur?

One side effect of UK rules that require companies to carry out age verification if their platform could contain inappropriate content is that some companies chose to simply block the UK rather than add that verification!

[url][/url]

Iain T wrote: ↑

Sun 08/30/26 8:36 am

Any chance of uploading the images to somewhere other than Imagur?

One side effect of UK rules that require companies to carry out age verification if their platform could contain inappropriate content is that some companies chose to simply block the UK rather than add that verification!

Yeah sure, Thanks to JMP I figured out the attachment option..
I just realized, one of the 2 50uf+50uf can caps is being used over at the input jack side of the circuit, so basically used as the V1 cathode bypass cap! Its also filtering the plates of V2. STRANGE... but it works and this amp has very little hiss.
The first photo shows the pots and the paralell 390ohm cathode bias resistors [195ohm total]. I changed those to a 10w 180ohm since I had one, but 5w would have been fine.

If they're not too big, you can share the photos here with the attachments tab under the post box. There's no need for 3rd party image hosting.

JMPGuitars wrote: ↑

Sun 08/30/26 10:47 am

If they're not too big, you can share the photos here with the attachments tab under the post box. There's no need for 3rd party image hosting.

Thanks! I always seem to find the hard way first...
The green, un-used 2k2 resistor in this pic of the board seems to have gone to V2 cathode pin 8, but its now using a shared cathode resistor/cap to ground. I contemplated un-doing the shared connection and using the 2k2 resistor, but there is no capacitor tied to that one, just a 2k2 to ground? So I kept the shared cathode connection with its 2k2 resistor + 0.1uf cap to ground.
The amp is buttoned up now so I'm just looking forward to using this ''mystery''
2x EL84 amp live in the not to distant future. It seems to like green, mid-humped overdrive pedals, no luck with anything else with that JBL in there, but the clean tones are perfect.