I call it the Simplexi - 1 knob, 8W, all you need

Marshall Amp Discussion

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Badside
Posts: 90
Joined: Wed Mar 24, 2010 12:40 pm
Location: Montreal, Canada

I call it the Simplexi - 1 knob, 8W, all you need

Post by Badside »

This is a build I made with the uPCB from the Wattkins forums, but it's fairly simple:

First triode is similar to a JCM800: 2k7/0.68uF on the first stage, 10k on the second (both have 100k on the plates)
In between is a 500k volume knob, preceded by a 470k/470pF treble peaker (so very JCM800-esque) that can be bypassed by pulling on the volume knob (I call this the Fat switch).
2nd stage feeds a MOSFET cathode follower because it was supposed to get a tone stack, now instead it goes through a 220k resistor then into the PI input.
PI is typical Marshall deal, except Rk is 470ohms and tail is 10k.
There is no NFB.

Power amp is a pair of 6K6GTs, which are kind of like an 8W version of the 6V6 (but they came before and I think they might be true pentodes), in fixed bias.

Diode rectification but there is a 180 ohms sag resistor.

Power transformer is a Hammond 269GX and in the end about 275V makes it to the plates.
Output transformer is a Hammond 1750PA, a Marshall 18W repro OT.

So there you go. Just one knob, from clean to way too dirty. Pull on it for more meat on the bone at the cost of tightness.

At 8W it's way too loud to play in an appartment, but at least it gets the speaker moving and is a superb power point for recording on playing in a club with a drummer.

https://youtu.be/8dSB-_naRSg
Amplifiers built:
Marshall 2204 head with some mods
Low-power 2204 (cathode biased 6V6s)
Single-knob dual-6K6GT amps using a Wattkins uPCB
AC30 clone with Plexified preamp section
AX84 Firefly
10thTx
Posts: 1863
Joined: Sat Dec 30, 2006 1:13 am

Re: I call it the Simplexi - 1 knob, 8W, all you need

Post by 10thTx »

That is a VERY cool amp! I really liked the tone you're getting in the YouTube. Bravo!

Thanks for sharing your success! IF you have a schematic, I'd love to see one.

with respect, 10thtx
joeboo88
Posts: 400
Joined: Thu Mar 28, 2013 8:51 pm
Location: Way up North

Re: I call it the Simplexi - 1 knob, 8W, all you need

Post by joeboo88 »

yeah Badside, I didn't see this post, sorry I missed it when it was posted almost a month ago.
sounds great.
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