This is a 5 tube guitar amp, PP EL84s...

My Nephew commissioned this amp as a high gain to replace his Mesa Boogie, which
was far too noisy and big and expensive - he sold it for about $1800...
amazing... anyway... I later plan to make a stereo version with 6L6s for 100
watts total.

This amp plagued me with problems from the beginning.... at first all it did was
oscillate and make horrible noises!

And it had too much gain...

Problems included:

Bad volume pot. (wiper would lose contact)
Leaky coupling cap
poor quality shielded wire (salvage!)
2 - bad solder joints (oops! who did that?!)
broken cap lead (stop playing with the parts placement!)


I finally tracked down the last bad joint - was the resistor on one grid of an
EL84... looked soldered but was loose... my spudger would cause a raspy noise
(oh how we LOVE that noise!) no matter where I touched the amp... really
frustrating and time consuming.


First 2 stages are a 12AX7 common cathode for pure gain... they have a small
parallel cap/resistor for tone EQ. and feed a GAIN pot.

This then feeds the BASS/TREBLE/VOL module, a sort of Bauxendahl circuit...

Then another 12AX7 as a gain recovery from the tone circuit and a common plate
amp to drive an active midrange tone circuit... this drives another 12AX7 that
is both a diff/amp phase splitter and part of the active mid...

This drives the EL84s.... cathode biased.

The power supply is a doubler, with 140VAC in, and a few series resistors here
and there to create a little 'sag', always nice in guitar amps...

Pre amp voltage is about 175v while power is 265v. Total filter is 350µF in 3
sections, plus two 22µF as the doubler.


The amp is VERY quiet, using a floating star ground and star power scheme...
even at high gain there is very little hum... At normal gain settings the hum is
inaudible.

I hope to put some pics and MP3s up on his web site soon...


So remember - no matter how bad your project may be on the first day, there is
always hope that it will be the best amp you ever made!

Bob