Can 100 W Plexi Kit Be Tweaked to be "All Clean"?

[yZe]

I am looking for those deep Marshall cleans w/ no breakup at high volumes

Does the Bass Plexi or Superlead kit allow for more headroom ?

How can the amp kit be tweaked at the onset in order to allow for high headroom cleans at stage volumes?

[VelvetGeorge]

Sure, to a degree.

I would try Bass specs with 12AT7's in the V2 and V3 positions. V1 if you can find one that isn't noisy there.

Also look at PA specs which are 99% the same. Generally no cap on the mixer resistors.

You can also increase the negative feedback in the output section.


VG

[yZe]

thanks for the quick reply

How would "no cap on the mixer resistors" for a PA system translate into the amp build?

Where would there be no caps on the plexi circuit?

Does increasing the values on the grid & screen resistors help toward headroom?

Would that mod affect the tone adversely ?

[Mars Hall]

6550 output tubes will also improve headroom. IMO the EL34 output tubes do not lend themselves toward a "clean" tone.

[yZe]

What does the power transformer have to be rated at to hande 6550's w/o melting down ?

Also,, are there mods that have to be done to handle the 6550's?

[Mars Hall]

I'm not an expert on transformers. It should work fine. The only thing to change are bias circuit resistors to set the voltage range.

[Roe]

get a 69 superbass kit (or a 45/100), change the 220k bias resistors to 150ks or 100ks, skip the 500pf mixer bypass resistor, and install new genalex kt88s, a 12at7 in v3, a 5751 in v2 and v1 (or try a 12au7 in v1 like the tweed amps)

also, try a 27k nfb resistor connected to the 16 ohm output (jtm specs) instead of the standard 47k

[908ssp]

And don't turn your guitar volume up all the way.