Metropoulos Forum

Has anyone made a marshall preamp with a trainwreck type poweramp? Is that even possible? I think I am going to try and make one.

please do tell how it turns out. do you use wreck spec transformers by the way?

What type of Trainwreck? Express? Liverpool? Rocket?

The power amp of the express is what i would like to do. I am still in the research phase. I remember copying Mark A when he wrecked a plexi the other way around. But since a wreck power amp can feedback more easily, I thought why not try to put some marshall magic on the front end.

I would use wreck spec trannys

The Express feedback isn't just the power amp, its the amp as a whole.

What do you really want to achieve?

germino is doing something similar with his new 35w amps

Isnt the Wreck power amp basically a JMP Plexi? 180uf filtering vs 192uf. Same Longtail PI values.. Feedback 47k/8 ohm tap. Plate Voltages are 400ish.. same as a Plexi back in 68'.

Its 100k/8ohm tap and has 6.6k impedance instead of 3.5k, so it only kicks out about 35W. As a result the negative feedback is basically the same as Marshall's 100K/4Ohm on their 50W amps. Also a 1K resistor is used instead of a Choke. So the power amp works a bit different to a Marshall but very similar.

Awe yes you are correct! I had to go check my Express to make sure I didn't stick a 47k in there!

So basically its changing out Plexi transformers for a Express set.

It would probably sound good with no complaints but these mad scientist projects for me usually end up with me wanting the original tone. From the different variations of the 18 watts Ive done.

Sorry I made a mistake, I meant negative feedback, not impedance. The negative feedback is basically the same.

I know what you mean about wanting the original tone. I'm like that and I keep telling myself that the next one will be my own design.......then I think of another original tone that I want . You should experiment though and see what you get. Play with the preamp .

RockinRocket wrote:Isnt the Wreck power amp basically a JMP Plexi? 180uf filtering vs 192uf. Same Longtail PI values.. Feedback 47k/8 ohm tap. Plate Voltages are 400ish.. same as a Plexi back in 68'.

No, the its quite different. the PT is rated for 300mA, not 150ma like a plexi. There is a 1k shared screen resistor instead of the 110ohms choke and the OT has a 6k6 primary, not 3k5

I didn't know this thread had other replies! sorry about that...

After looking into the design some more, I decided to just make a complete Express amp. I already have the chassis, Pacific transformers, and several other components ready to go. I will keep you guys updated about the project as it progresses.

Awesome amp. Here's mine:







Took a good bit of effort to dial it in, but it's a fantastic amp.

what a beauty! I will try and get some work done on the chassis this weekend.

This is what I have so far. Drilled a hole in the front for the PPIMV.