....and Now for Something Completely Different!

[10thTx]

Thanks so much for sharing the schematic and layout! It is appreciated.

Nice amp! Great tone and great playing.

With respect, 10thtx

[M Fowler]

David I enjoyed your playing the amp sounded great.

[David Root]

Here's the new revised farther-off-the-range schematic for a 2xKT88 SE UL. I have already bought the chassis and the iron, see pic.

Comments welcomed. I changed it to fixed bias so I could get away with a 200mA PT, and also to put a DC coupled CF like a Steel String Singer. There is a bit different HRM tonestack on the overdrive side. Thanx to JD0x0 for that!

I hope these TV tubes sound good. They are so much cheaper than 5879/12DW7.

Not yet shown is an active loop which I want to include. Anyone done one with a 5751, and if so how is it?

[TUBEDUDE]

It might need a more elegant relay circuit to minimize the pop when switching channels.

[David Root]

That had occurred to me, so I raised the question with Colossal (Dave Cohrs), who builds the relay boards and relay PS boards I use.

He suggested the attached, which I'll plug in to the schem if I can do it without making it illegible. Just imagine the two .02 caps are actually .2, as I had put .01 in the original schem by mistake instead of .1, which is what is needed for about a 100 Hz roll-off in the feedback.

[TUBEDUDE]

Let us know how that works out.

[David Root]

That has been superseded by this arrangement which keeps the DC off all the relay contacts. Note that the cap values are now correct for ~100Hz rolloff in the feedback. They were wrong by a decimal point slip!

I'm also going to add a 12AX7 or a 5751 in parallel in front of the 6U8 in order to be able to solidly overdrive the 6U8 pentode as the guitar pickups alone won't reliably do that. Well, humbuckers might but even that's not guaranteed.

[David Root]

Just wanted to show you the finished SE KT66 amp. (This is not the 2xKT88 SE circuit above, but the earlier one).

Nice lascivious lizard finish, no?

Headbox by Taylor Cox, Amplified Nation, faceplate/backplate by Joe Vallina, Amplates.com. '55, '56 RCA 5879, '70s Sylvania 12DW7, Shuguang KT66.

Changed the .05 uF screen bypass cap in the 5879 driver to .1 uF. That and using a Epi 335 with a 7.4K neck pickup I wound myself now gives lots o'bass!

[M Fowler]

Looks good and gig ready.

[gmgaudio23]

Hi.

I know it's an old post... But had anyone made this "upgraded" version of amp? It's a pity that such an interesting theme just stopped!

[John_P_WI]

Sadly, David is no longer with us.