Fender Ultralinear - KT66, 77 or KT88?

[Shawnobi]

Considering a tube change on my 70w Ultralinear Pro Reverb.

I've heard talk of replacing the 6L6's with KT66's, 77's or even KT88's. Can anyone shed any light on this, esp with the KT88's? Is it actually 'plug & play'? Suggestion is that the huge UL transformer is man enough for it.

[potatofarmer]

I had a similar thought not too long ago; lot of good responses from people smarter than me here: http://music-electronics-forum.com/t35295/

What's your motivation for wanting to do so?

[Shawnobi]

What's your motivation for wanting to do so?

Mindless tweaking

[Leo_Gnardo]

I had a similar thought not too long ago; lot of good responses from people smarter than me here: http://music-electronics-forum.com/t35295/

What's your motivation for wanting to do so?

KT-88's? So you can sound like a Sunn?

I have used KT88 in Marshalls & Ampeg SVT, no ultralinear OT's, but they work well and sound terrific. Nice change from the usual EL34 or 6550.

Might have to try 88's for a lark next time a UL Twin comes thru the shop.

I've tried KT77 in guitar amps. Only one brand of amp accepted them well: Burman, a rare UK made amp designed with 77's. In other amps they were just fine up to the clipping point, then clipped in a non-musical way, ugly distortion.

[potatofarmer]

Mindless tweaking

Unfortunately it requires some mindful tweaking. You'll likely need an additional filament transformer as any of the tubes you mentioned will draw more heater current than the 6L6GC. You'll probably have to double your speaker load per tap, and the power output will stay the same. You'll probably also need to modify your bias supply.

Can it be done? Sure. Is it plug-n-play? No.

[potatofarmer]

KT-88's? So you can sound like a Sunn?

I have used KT88 in Marshalls & Ampeg SVT, no ultralinear OT's, but they work well and sound terrific. Nice change from the usual EL34 or 6550.

Might have to try 88's for a lark next time a UL Twin comes thru the shop.

I've tried KT77 in guitar amps. Only one brand of amp accepted them well: Burman, a rare UK made amp designed with 77's. In other amps they were just fine up to the clipping point, then clipped in a non-musical way, ugly distortion.

I still haven't gotten around to trying it, to be honest. I don't have a ton of money available for project work, and when the chance comes up that I've got $50 to spend on parts, replacing tubes that are already working fine is pretty low on that list. I guess I should've updated that thread - I realized after I measured the screen dissipation that my calculations were independent of the screen stopper, so the rule of "ultralinear doesn't need screen stoppers to be safe" seems to hold even for these odd Fenders. Still good to have stoppers, of course, and with the 2k/5W I'm not worried any more about the 6L6GC taking those conditions. Plus, I mean, if these things ate tubes like popcorn, I'm sure someone would've noticed at some point in the past 30 years.

I still want to try it someday, so if your lark ever happens, let me know.

[Shawnobi]

KT-88's? So you can sound like a Sunn?

I have used KT88 in Marshalls & Ampeg SVT, no ultralinear OT's, but they work well and sound terrific. Nice change from the usual EL34 or 6550.

Might have to try 88's for a lark next time a UL Twin comes thru the shop.

I've tried KT77 in guitar amps. Only one brand of amp accepted them well: Burman, a rare UK made amp designed with 77's. In other amps they were just fine up to the clipping point, then clipped in a non-musical way, ugly distortion.

Friend of mine has some Burman gear. Very nice indeed.