Merlin's Ultra High Gain preamp

[M Fowler]

I'm dragging ass today but did some more work this morning but got a long way to go before fire-up.

I took the lovely Mrs out for lunch and shopping, took a nap and now might get some more done.

Mark

[statorvane]

Looking good - real good. Also very nice chassis, where did you get it?

Is this from Merlin's Preamplifier design book;1st or 2nd printing?

[M Fowler]

From his book yes title, volume, page and figure indicated in previous post by Martin Manning.

This chassis I think is from Mojotone JTM45 with front and back plates.
I built two JTM45 heads and this was a left over which works perfect for the Fender PT, OT (4,8,16R) and choke I'm using
from hoard. (Super Reverb type transformers).

Mark

[RockinRocket]

Looking great Mark I've wanted to try one of Merlin's high gain designs and was just analyzing this circuit.
Let us know if the circuit is a worthy choice.

[Rockwell666]

I am very curious to how this circuit sounds as well. all plate driven. that noisegate looks like it is just clipping diodes to filter and saturate the signal...wonder how it sounds

[M Fowler]

I'm wiring on it today doing the filaments right now then the board/pot wiring.

Been taking care of my wife and sons battling heart issues and had to repair a Marshall JCM800 combo POS poor repairs/bad PCB tracings melted down power switch and PT.

Mark

[Matt J]

I'm wiring on it today doing the filaments right now then the board/pot wiring.

Been taking care of my wife and sons battling heart issues and had to repair a Marshall JCM800 combo POS poor repairs/bad PCB tracings melted down power switch and PT.

Mark

I hope your wife and son feel better soon Mark! That's always a rough thing to go through!

- Matt J.

[M Fowler]

Thanks they are getting better each day which is amazing.

[M Fowler]

Should be able finalize and fire this amp up today.

Gut shot Merlin's High Gain Preamp.jpg

[M Fowler]

Fired it up and too much gain V1 so lowered to 5751 tube.

Very high gain circuit. Sounds best with boost engaged.

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LLP

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[Matt J]

Looks awesome!!

Did you change anything in the power section from a stock JCM800?

- Matt J.

[M Fowler]

No just used a 50/50 can cap is only change. With 20uf on the board.

Used odd PT - Super Reverb type and 40w Hot Rod Deluxe OT

Fender 6L6 choke.

[RockinRocket]

Looks great and a lot of fun!
I think I might give it a try.

Did you by any chance consider Merlin's LTPI improvements?
Small couplers,
Larger cathode 1k and 22k tail.
100k grids?

He also wasn't to found of the blocking distortion of the global feedback circuit.

[dorrisant]

Looks nice!!

How high is the gain? Anything to compare it to?

[M Fowler]

The gain much more than a JCM800 and more like the Friedman BE without all the ERA switching.