Ideas, Impressions, Schematic Suggestions for 807's

[zippy1540]

A friend of mine just ran into a bunch of 807's and wants me to build an amp for him. He has a bunch of 6sn7's also. Anyone have any suggestions for a push pull schematic i can build him? I'm thinking i'll need a 12x7 or 6sl7 and use the 6sn7 as the phase splitter. For anyone who has built an amp using 807's what operating points seem to work best? output impedance?
Just gathering ideas at this point, the power supply will probably be a tube rectified CLCRC setup but i'm not too worried about that.
Thanks,
Paul

[andrewbee]

Hi,

Look at 6l6 circuits, pretty much the same tube electrically.

For some reason I am attracted to this one http://lagarto-ex-infoseek.jp/shishido/ ... 6PPSHI.png

Andrew

[kheper]

A friend of mine just ran into a bunch of 807's and wants me to build an amp for him. He has a bunch of 6sn7's also. Anyone have any suggestions for a push pull schematic i can build him? I'm thinking i'll need a 12x7 or 6sl7 and use the 6sn7 as the phase splitter. For anyone who has built an amp using 807's what operating points seem to work best? output impedance?
Just gathering ideas at this point, the power supply will probably be a tube rectified CLCRC setup but i'm not too worried about that.
Thanks,
Paul

Old STC datasheet with a few amp schematics:
http://nekhbet.com/STC807.pdf

10K is the recommended primary output impedance. If you cannot find one, placing 8ohm speakers on the 4ohm tap of a 5K output transformer will achieve the same result.

You can run the 807 in UL mode (even though the screens have a max 300V rating) at 450V, as long as the max plate dissipation is NOT exceeded. (400V would be better.)



Older designs, such as below, ran in triode mode at 400V:

[Shannon Parks]

Easy Clementine build.

Shannon

[zippy1540]

My first thought was a clementine but my buddy is looking for rock concert chest thumping volume. He's got an impossibly large wall of speakers in a really small room. Klipsch corner horns, 2 sets of cornwalls, Klipsch mini corner horns, and a set of large speakerlabs. I brought over my clementine with el34's before i sold it and he liked it except for the lack of high volume. What about using the Eiclone schematic tailored to the 807's? I would work the power supply to match some good operating points for the 807's. possibly PPP. Any suggestions on the ideal operating point for the 807 in PP?

[kheper]

I would work the power supply to match some good operating points for the 807's. possibly PPP. Any suggestions on the ideal operating point for the 807 in PP?

For the plate voltage and the idle bias current - to maximize tube longevity:

400V * .0425A = 17W

Shannon's st-70 board will work well with 807s.

Pete Millet has a driverboard for PPP 807s. For outputs, he uses the Dynaco MKIII clones:

http://www.pmillett.com/807pp_amp.htm

[Shannon Parks]

Shannon's st-70 board will work well with 807s.

Yeah, doing an 807 ST-70 is easy. Actually, Thermion and I need to sweep his and verify the feedback tuning values.

Shannon

[zippy1540]

What about a cathode biased Eiclone setup? I like the idea of using all octal 6sl7/6sn7 front end. My buddy is really insistent on monoblocks and point to point wiring. This is in the early planning stages since he's gotta sell some of his picker hoard to fund this project. I''m a big fan of lots of planning prior to even ordering parts.
Thanks,
Paul

[kheper]

What about a cathode biased Eiclone setup?

The guy who rebuilt the RCA amp below maintains that the 807s ran hot with cathode biasing, so he went with fixed. However, the B+ was 680V!

http://www.montagar.com/~patj/mi12188a.htm

The 807s will work in the Eiclone, but you may need to tweak the feedback, bias, B+, etc.

[zippy1540]

I know points will have to be tweeked but i liked the eiclone topology. For those who have played with 807's what is your recommended operating points? Transformer impedance? I'm looking at going cathode biased possibly with a CCS.

[kheper]

I know points will have to be tweeked but i liked the eiclone topology. For those who have played with 807's what is your recommended operating points? Transformer impedance? I'm looking at going cathode biased possibly with a CCS.

See my above posts.

plate voltage = 400V
plate current (idle) = .0425A
plate dissipation = 17W
load impedance: 10Kohm

10K is the recommended primary output impedance. If you cannot find one, placing 8ohm speakers on the 4ohm tap of a 5K output transformer will achieve the same result.

[Gingertube]

That ACROSOUND scheamtic above should be good for 807 and 6SN7.
For 807 Application data see here:
http://www.retrovox.com.au/STC807.pdf
Caution 5.5 MByte, but everything you ever wanted to know about running 807s.

Many 807 tehse days go toward a Standell Guitar Amp Clone.

Cheers,
Ian

[Impmon]

A friend of mine just ran into a bunch of 807's and wants me to build an amp for him. He has a bunch of 6sn7's also. Anyone have any suggestions for a push pull schematic i can build him? I'm thinking i'll need a 12x7 or 6sl7 and use the 6sn7 as the phase splitter. For anyone who has built an amp using 807's what operating points seem to work best? output impedance?
Just gathering ideas at this point, the power supply will probably be a tube rectified CLCRC setup but i'm not too worried about that.
Thanks,
Paul

Lucky him. 807s can work great if you take the necessary precautions with the design. 807s like to make higher order harmonics, so some form of local NFB is a good idea. They also like to make snivets, so screen stoppers are mandatory. Once you have those problems taken care of, they perform with excellence.

Suggested schemo: Vixen (attached)

This design puts everything you mentioned to good use: 6SN7s, 6SL7s, and 807s. Also included: active screen regulation as having a stable, Lo-Z source for the screens improves linearity. This is a feature seldom seen with commercial designs, and very few professional designs. One exception was a theatre amp that used 807s as finals. The regulator can be hollow state, or solid state with high voltage MOSFETs.