The Amp Garage

As for the chassis I decided to create a 3D drawing (Fusion 360) with all original dimensions from the K60 drawings (converted to mm) and to custom order a chassis. All holes and openings are defined as parameters, and can easily be adapted eg. for different trannies or different component diameters...

Funny, I also plan a Komet style amp (Concorde) and asked Heyboer for support. I didn’t get a reply either, for whatever reason, they don’t like to handle single customers (or they don’t need to…). Since Rosamp is based in the UK, I recommend to get in touch with Michael from Modulus Amplification. ...

I did some intensive research on the Concorde and found highly valuable information like the Asteroid schems and layout plus the adaptions required for the Concorde. However, I struggle in ordering the correct Heyboer tranny set with the 4,8k OT here in Europe. Mojotone (no customer orders at this t...

Hi Phil,
Did you manage to finish your project?
I’m asking because I would be highly interested in building this Lil Devil. I already built a Trainwreck Express clone, but this amp is just too loud for frequent playing…
Thanks,
Frank

Good question. FWIW I used only SBE6PS and 416P in my build.

Colossal, thanks for you time to have a close look at the photos. Good catch with the cathode lead to V1b p3, it is punctured indeed, I will replace it. I will check and re-do the anode connection on V1_pin 6. 10k input resistor: done. C2 is hidden from C3 (huge orange drop). I was told that micas m...

Any ideas at all where the bass heavy behavior of my amp could come from? The low end is booming and really annoying then something seems wrong. recheck the wiring of the tonestack I re-checked all pots and connections: Tone stack pot values: - Vol (1MA): Alpha A1M (measured value 1,03M) but now sh...

Excessive bass can itself be a symptom of oscillation, in rare instances. Do you have an oscilloscope? Use it to watch for oscillation. I have to say, I don't like those orange drop caps in there very much. I favor MKT1813 series Vishays. They're about as close as you can get to a modern Philips Mu...

then something seems wrong. recheck the wiring of the tonestack

Will do,thank. I'll keep you posted after the check.

yeah, tried this already Thanks eddiep1966 for the hint, though.

Any ideas at all where the bass heavy behavior of my amp could come from? The low end is booming and really annoying...

I already disconnected the NFB wire (R22/100k detached) as one of the first measures. Sound and playing feel changed, but squeal was still there.
Let me re-check...

in the meantime I went closer to the original circuit (C9 back to 0.1uF, took out the cut control) and tried out some measures: twisted the wires from the phase inverter to the el34 grids bigger grid resistors 39k at the power tube sockets grid resistors 68k at v2 and v3 (pins 2 and 7) adjusting the...

Roe wrote: ↑Wed Jun 18, 2025 7:29 pm try to twist the wires from the phase invert to the el34 grids. bigger grid resistors downstream also help with oscillation and blocking distortion. try 47k at the el34s and 68k at v2 and v3

Thanks, I'll try over the weekend and report back.

Tone stack wiring is very sensitive, so try moving leads around with a chopstick and looking for any that affect the tone of the squeal. Does the bright switch affect it? I agree on the heater elevation, none needed unless there is a cathode follower that runs Vh-k near spec limit. I tried as much ...

It's a sensitive design. Use high gain preamp tubes and turn it up and it's going to squeal at some point. Hand pick preamp tubes that balance the available gain. And don't expect that this amp can ever be dimed on all controls and remain stable. This is a high performance thoroughbred racehorse of...