GM70 an 813 strapped in SE-UL - circuits?

[otto88]

Does anyone have a tested circuit for a GM70 SE, or PSE; an 813 strapped in SE-UL?

My main speakers (Apogee hybrids) are only 84 dB, so 100 watts would be preferable. Though it might add too much to an already substantial project . .

I could go KT88 PP UL/ pentode mode, but would probably prefer SE.

How many watts would an 813 strapped in SE-UL produce?

Any suggestions on sources for OPTs and 240 volt power transformers?

Thanks

[Cobra2]

I have seen 45W in UL-SE mode. If you paralell 2 x 813, you shuld get close...

Arne K

[otto88]

Thanks Arne,

Parallel UL SE could be the way to go.

It doesn’t have to be an 813 -

I have read that eg of the 6V6, 6L6, 5881, EL34, 6CA7, KT66, etc clan, the KT88 is best for running in ultralinear mode.

How can the suitability of tubes for ultralinear be determined?

Thanks

[andyjevans]

I sympathise - I have Apogee Caliper Sigs.

First thing is, depends on room size. I drive my Apogees with a PPP 6S4 amp - can't be more than 10 watts. A SE300b wouldn't drive them at all. A PP KT88 amp drives them fine - all this in smallish rooms. So if your room is not too big, I'd say go with PP300b or PSE 300b.

I'm thinking 813 myself - I've bought a stock. Personally I build all DHT - not interested in the directly heated valves unless I have to use them for some reason. I prefer the sound of DHTs.

I'm thinking push pull 813 myself. I like SE but it's more important to me to be using DHTs. I don't want to go high voltage so I'm thinking 450v. But with 813 you can go higher.

Andy

[Bandersnatch]

hey-Hey!!!,
I have a similar valve to 813 running U-L at ~550V, the 4E27. Nearly pin-compatible with the 813, but at 5V instead of 10V on its cathode. I have special outputs made with multiple taps, and taken from the Peerless S-265-Q coil geometry.

I will swap to 813 as soon as my leisurely collection of a quad is complete. The filament supply is easily converted too... Bias will be similar. The U-L percentage is critical for the load matching; it changes the operating elvelope of the plate curves.
cheers,
Douglas

[Pyre]

Hello,

Have you checked out the GM70 group on Yahoo. Lots of tested schematics and advice.

http://groups.yahoo.com/group/GM70/

I am building a tubelab SE board driving a pair of GM70's right now but its in the build stage not the tested stage yet.

Shane

[otto88]

Andy

Apogee Caliper Sigs with 10 watts? Even in a modest room, that’s amazing!
Apogee guru Graz suggests that Apogees need plenty of watts to sing to their best . .


I have only Centaur Minors, and 50-150 watts is recommended. The room is 5.3 * 6.7 * 3.5 m (c 17’ * 21’ * 12’) so I think I need 50+.

Douglas

> The U-L percentage is critical for the load matching; it changes the operating envelope of the plate curves.

Maybe its best to get OPTs with taps at say 40%, 50% and 60%, to allow thane amp to be better optimised.

Shane

I’ve been to the GM70 Yahoo group a little, but hadn’t seen much there. I should go look more.

Has Tubelab said that his SE board could be used for GM70's?

What power and output iron will you use?? $?

Cheers

[otto88]

Shane

How did you determine the (initial) component values for the SE board with GM70's?

[Richard Ellis]

Hows' this...An 813 strapped in UL.
_________________________________________Rick..... ........

[Bandersnatch]

Originally posted by otto88


Douglas

> The U-L percentage is critical for the load matching; it changes the operating envelope of the plate curves.

Maybe its best to get OPTs with taps at say 40%, 50% and 60%, to allow thane amp to be better optimised.

hey-Hey!!!,
Go lower than 40% too; on this I must say, " you may be pleasantly suprised ".
cheers,
Douglas