Marshall Pre / Trainwreck Power

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metalhead3ecr
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Marshall Pre / Trainwreck Power

Post by metalhead3ecr » Tue Jan 03, 2017 9:41 pm

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.

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Re: Marshall Pre / Trainwreck Power

Post by Roe » Wed Jan 04, 2017 7:35 am

please do tell how it turns out. do you use wreck spec transformers by the way?
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Re: Marshall Pre / Trainwreck Power

Post by d95err » Wed Jan 04, 2017 8:28 am

What type of Trainwreck? Express? Liverpool? Rocket?

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metalhead3ecr
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Re: Marshall Pre / Trainwreck Power

Post by metalhead3ecr » Wed Jan 04, 2017 8:33 am

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

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Re: Marshall Pre / Trainwreck Power

Post by Littlewyan » Sat Jan 21, 2017 2:50 pm

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

What do you really want to achieve?

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Re: Marshall Pre / Trainwreck Power

Post by Roe » Sat Jan 21, 2017 3:20 pm

germino is doing something similar with his new 35w amps
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Re: Marshall Pre / Trainwreck Power

Post by RockinRocket » Sun Jan 22, 2017 7:57 pm

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'. :D

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Re: Marshall Pre / Trainwreck Power

Post by Littlewyan » Mon Jan 23, 2017 1:39 am

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.
Last edited by Littlewyan on Mon Jan 23, 2017 6:36 pm, edited 1 time in total.

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Re: Marshall Pre / Trainwreck Power

Post by RockinRocket » Mon Jan 23, 2017 6:06 pm

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.

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Re: Marshall Pre / Trainwreck Power

Post by Littlewyan » Mon Jan 23, 2017 6:40 pm

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 :P. You should experiment though and see what you get. Play with the preamp :).

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Re: Marshall Pre / Trainwreck Power

Post by Roe » Tue Jan 24, 2017 4:13 am

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'. :D
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
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JTM45 RS OT JTM50 JMP50 1959/2203/34/39

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Re: Marshall Pre / Trainwreck Power

Post by metalhead3ecr » Wed Feb 08, 2017 1:47 pm

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. :thumbsup:

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Re: Marshall Pre / Trainwreck Power

Post by Winder » Wed Feb 15, 2017 8:38 pm

Awesome amp. Here's mine:

Image


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

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Re: Marshall Pre / Trainwreck Power

Post by metalhead3ecr » Thu Feb 16, 2017 9:35 pm

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

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Re: Marshall Pre / Trainwreck Power

Post by metalhead3ecr » Sun Feb 19, 2017 11:06 am

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

Image

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