Switching to KT88's from 6L6's..

[leadfootdriver]

Well, it didn't blow up, but I only played it for a little while.. I did max it out with the Rivera Rockcrusher Attenuator for a minute or so..
The Amp is a Jet City JCA 50 112 combo..Not sure on the specs for the IT or OT, but the OT is a good size.. I have a Hammond 1650KA OT for 50 watts Ultra Linear, and the Jet City is actually bigger..
I biased it up for 70 watts at 70% at like 54ma's.. Plate voltage came in at about 450V..
The Screen Resistors are the stock 470R's.. The Amp does have a 10H Choke..
My Fryette Amps run 1K5W's with their KT88's.
Should I put the 1K5W's in there??

I don't love the sound of this amp. It's super compressed and gainy but the KT88's filled in the sound along with running some lower gain tubes opens things up a bit..

[leadfootdriver]

I'm guessing that I'll fry my Heater taps.. I bet I'd be good if I could get a 100 watt PT..

[J M Fahey]

Not sure what´s the point of doing "power increasing" mods, to the point of endangering amp, and then running it into an attenuator.

[leadfootdriver]

I'm a guitar player.. Guitar players are tweakers..
Don't need anymore power.. This amp is a turd.. I don't mind modding it if I can learn something.

[glebert]

I don't think you learn much from randomly changing tubes, resistors, and transformers, especially if you end up just destroying stuff. I would say if you want to learn compare the schematic of an amp you like with the Jet City and see if you can make small changes that help.

[pdf64]

…
I biased it up for 70 watts at 70% at like 54ma's.. Plate voltage came in at about 450V
…

It’s scenarios like this that turn the guideline ‘set bias to idle the output valve anodes at 70% (or whatever)’ into a joke.
I suggest to draw up the loadlines and select an operating point that’s suitable for the amp and the output devices. Rather than just bunging them in and increasing the loading on a probably already overstressed PT.

I'm guessing that I'll fry my Heater taps...

Very possibly.

[leadfootdriver]

This forum is loads of fun today..

[pdf64]

Actually, the probable loadline looks ok.

So the concern is whether the PT can cope with the high loads on its heater and HT windings.

[The Dude]

This forum is loads of fun today..

Well, you've done a modification to the amp that likely nobody here would recommend. And then you say, "I'm guessing that I'll fry my Heater taps", so you already know it's a bad idea. I'm not sure what comments you expected. I'll add, IMO, there's little to be gained by changing from 6L6 to KT88, except for potential damage to the amp. You'd be better off doing small preamp mods to get what you're after, as has already been said.