Looking for a LTP PI>pair of KT88 schem.

[fusionbear]

Hello again. I want to build another clean amp. This time I want to build a simple fender style tone stack into a LTP PI into a pair of KT88's

Any body have a power amp schematic they could share?

I'm thinking of using a M style power transformer with about +480 at the plates.

12AX7a>tonestack>12AX7b>12AT7 PI> 2- KT88's

I am assuming the 12AT7 will drive the KT88's better?

[soma_hero]

Sunn 200S. The only thing that matches your description is the 2xKT88 output.

Two triode stage, pentode stage driving triode concertina.

Great sound, and interesting design.

[Roe]

standard values work fine but decrease the 220k bias splitters to 150k or even a little lower.
If you want the 12at7 to really drive the kt88s try 47k plate resistors and a 270k cathode resistor ala BF fender. it will sound punchy but less compressed

[fusionbear]

Thanks guys!

I was aware of the Sunn, but didn't want to get that complex.

[soma_hero]

The Sunn only has 2 preamp tubes since it uses a single package triode/pentode. Pretty simple, but yes very different then usual.

[fusionbear]

The Sunn only has 2 preamp tubes since it uses a single package triode/pentode. Pretty simple, but yes very different then usual.

My Weber Sunn clone of the S100 is similar:

5751a>gain stage>5751b> Marshall type plate fed tonestack>EF86 Recovery and driver>12AU7 PI in Cathodyne config.> 2- KT88's

I like it a lot, but want to experiment with a Fender type tonestack

[Ian444]

What's the expected grid bias voltage for KT88's, is it much more than for EL34? If it isn't much more, than any LTP schem for 4 x EL34 should be close. Another scheme is the Marshall Major with a cathodyne feeding seperate drivers, that will have no trouble driving KT88.

[bb5000]

Running KT88's at 660-670 Vp, 40 mA cathode current with -70 VDC at the grid.