Watkins Dominator Mk 3

[CJ]

EL84 driven by a 12AX7a inverter and a 12AX7a preamp

preamp features a Fender/Marshall type tone stack,

this thing rocks, i ripped out the AC 15 trem channel and tried it out, plays clean with the chime until half way up the volume pot , then it turns into a monster with sweet crunchy overdrive,

i kept the ef86 which has it's place especially with low volume work.

both channels feed the inverter just like the vox and this circuit.

so kind of an AC 10 with tone controls, do give it a try.

 

[CJ]

watch this old man tear the house down>

 

[CJ]

other WEM schemos>
http://wem-owners.com/schematics/dominators/
lots more real estate, simple amps seem to sound the best,

this was also an Elpico for a few days so we have some clean up to do, like ripping out two tube sockets,

 

[CJ]

added vox tone network to both channels

amp does not break up so soon now

might put an assign sw for each, so les paul or strat, dial it in,

 

[CJ]

amp sounds great but when pushed hard sounds like a cheese grater,

found this Paul Ruby mod with zeners on the grids of the el84's to ease the cross over distortion,

what this does is make the bottom of the wave form match the top half by simulating grid blocking with the zener diodes, so it is like both top and bottom getting grid blocked instead of just the top, so is not volume limiting but wave matching, which reduces speaker spike problems, i think,

wiring it up right now...

https://www.18watt.com/storage/18-watter_buzz_info_311.pdf

 

[CJ]

scope shots of one side of phase inverter output after coupling cap but before grid stopper resistor,

so we put in dual networks, and the amp sounds better when cranked,

 

[CJ]

i used a slightly different network than the Paul Ruby mod,
a 12 volt zener and 1n4001 were used with a series resistor instead of mixing and matching series string zeners,

i put the amp on the scope and watched the results as different resistors were tried, the lesser resistors cutting out more of the crossover distortion, using the max resistance needed to do the job as to not cut power or mess up the tone,

interesting to note that power actually goes up with the mod as duty cycle is improved,

the 1n4001 keeps the positive half of the wave from shorting thru the zener to ground,

the resistor keeps the zener from getting hot from too much current during clamping,

 

[Gus]

CJ you posts reminded me of the blue guitar web site
IIRC I think there was a diode limiting circuit shown there may years ago for Marshall 18 watt circuit

https://blueguitar.net/schems.htmhttps://blueguitar.net/

 

[fazer]

I got to try this. I have an amp with EL84s. I was thinking Trainwreck concord but this could be cool no matter which way I go. Also want to try the ef86. Thanks CJ