Fuchs Blackjack 21 v1

[Gainzilla]

Hey all,

Picked up a Fuchs Blackjack 21 recently. Great sounding amp. They say it's supposed to be TW inspired, but it only has 2 preamp tubes as well as the pair of 6V6's. Not terribly loaded with Gain. That can only lead me to believe it's based on one of the "Blues" Rockett variations with a cathodyne PI and 6V6 instead of the EL84's as per usual.

I've reached out to Fuchs to see if they'd send a schematic. They don't feel like doing that, so I asked them to specify the general topology. Barring that, the PCB looks really simple. If anyone is interested, I'd probably be up for a go at posting pics and tracing out a Schematic. Who's up for it?

Bryce

[pompeiisneaks]

Andy Fuchs is a regular poster here, he may speak to it. If not, just the name makes me 'think' a blackfaced fender style amp. It might also be loosely based on the Dumble Overdrive Special that's a little less of the full functionality, or even just a lower output setup with dual 6v6's? The manual shows the control panel and it has a drive section which is more like the dumble method.

Not sure though. Posting pics of the guts would be a good start yes, several members know different topologies pretty well and may have a pretty good idea.

~Phil

[Gainzilla]

I received a polite request to not trace the board out publicly, so I'll honor that request.

That said, I did get a rough description from them. "basically two gain stages into a cathodyne with fixed bias. I believe one tube section was either paralleled or not used on the driver tube tube."

I'm not sure it can have an unused triode and still be a TW circuit with a Cathodyne PI. That would be true if it had a LTPI. Therefore, I believe it's something like the following:

A5H_BluesExpress.png

[rooster]

Looking at that schematic, ignoring the sonic circuit side of it, the power supply AC connection could actually electrocute you. You see this right? The AC hot wire (Black) should go through the fuse and then the switch and then connect to the primary, the return AC path (White) should be a solid connection to the tranny primary.

The circuit you present...imagine the fuse blows and the guitar player makes contact with a ground path? Zapp City. I hate to see things like this on this site.

[sluckey]

The circuit you present...imagine the fuse blows and the guitar player makes contact with a ground path? Zapp City. I hate to see things like this on this site.

NO WAY!

[romberg]

I'm not sure it can have an unused triode and still be a TW circuit with a Cathodyne PI. That would be true if it had a LTPI. Therefore, I believe it's something like the following:

That has 3 gain stages with pretty much no attenuation between stages ('cept for the tone stack). This is the same as an express. This is all the gain you need to overdrive the power tubes (which is what an express/liverpool does). Does your amp have the master volume shown in the schematic? If so, that is the problem with having little distortion.

An expres/liverpool preamp does not have much distortion on it's own. It is all about the power tubes. Which also means it is all about LOUD. I bet it can get pretty mean if you crank the master all the way up and set the volume around five or six.

Mike

P.S. If this is too much volume, there are other master volumes that work better here. I think a PPIVMV is much better than the pre PI master here.

[FUCHSAUDIO]

Looking at that schematic, ignoring the sonic circuit side of it, the power supply AC connection could actually electrocute you. You see this right? The AC hot wire (Black) should go through the fuse and then the switch and then connect to the primary, the return AC path (White) should be a solid connection to the tranny primary.

The circuit you present...imagine the fuse blows and the guitar player makes contact with a ground path? Zapp City. I hate to see things like this on this site.

If you are referring to the AC wiring in the Trainwreck schematic, that's the typical Fender (and thousands of others) AC wiring. Split the AC between fuse and switch and then to transformer.
It changed in later year, but in the 40's through 60's was very common.

[pdf64]

Looking at that schematic, ignoring the sonic circuit side of it, the power supply AC connection could actually electrocute you. You see this right? The AC hot wire (Black) should go through the fuse and then the switch and then connect to the primary, the return AC path (White) should be a solid connection to the tranny primary.

The circuit you present...imagine the fuse blows and the guitar player makes contact with a ground path? Zapp City. I hate to see things like this on this site.

Whilst not in any way defending fusing the neutral, as I see it, provided the user doesn’t simultaneously touch the transformer side of the fuse with one hand, earth or neutral with the other (which should be as unfeasible as touching live), the user should be ok.
Even if live shorts to the chassis, provided the chassis has a solid electrical connection back to planet earth and the breaker / fuse in the consumer unit is suitably sized, all should be well.
The hazard seems fire, rather than electrocution.

[Mark]

I received a polite request to not trace the board out publicly, so I'll honor that request.

That said, I did get a rough description from them. "basically two gain stages into a cathodyne with fixed bias. I believe one tube section was either paralleled or not used on the driver tube tube."

I'm not sure it can have an unused triode and still be a TW circuit with a Cathodyne PI. That would be true if it had a LTPI. Therefore, I believe it's something like the following:


A5H_BluesExpress.png

This was the work of the late Steve Ahola. He did a lot of good work with Trainwreck circuits and tried a lot of mods and transformer sets with these amps.

https://ampgarage.com/forum/viewtopic.php?t=31564