Is anyone usig 807s?

[Helmholtz]

Some design considerations with 807's, based on datasheet limits:

It's a 25W PD tube with plate and screen voltage limits of 600V and 300V respectively.

Because of the low screen limit, the rel. high plate voltage limit cannot be utilized with class A, UL or triode operation.

For max. output power and a B+ of 600V rather cold biased class AB should be used.
The datasheet specifies an idle current of 18mA@600V for an output of 56W (wondering if the idle current is large enough to eliminate crossover distortion).
To maintain a B+ of 600V at full output, B+ at idle might have to be higher by 10% or more, exceeding the tube limit.

The OT needs to have a primary impedance of 10k.

For comparison, a pair of EL34s allows for around 100W output with a B+ of 800V and 25mA idle current.
I own an old Siemens amp that is built accordingly. Measures above 90W before clipping.

[Mick Bailey]

With my own experiments with the tubes I've found them to easily exceed the specs overall, but some examples will arc internally if the plate voltage is too high. Finding modern EL34s that will stand 800v is a challenge - I've had limited success with Shuguang and recent old stock (late 90s) Svetlanas in some amps that run a high-ish B+ (Traynor, Hiwatt), but mostly EL34s have a hard time at anything over 600v.

[Helmholtz]

With my own experiments with the tubes I've found them to easily exceed the specs overall, but some examples will arc internally if the plate voltage is too high. Finding modern EL34s that will stand 800v is a challenge - I've had limited success with Shuguang and recent old stock (late 90s) Svetlanas in some amps that run a high-ish B+ (Traynor, Hiwatt), but mostly EL34s have a hard time at anything over 600v.

While I don't have much experience with modern EL34s I think the main problem is not high B+ but high screen voltage.
When operating at 800V B+, screen voltage must not exceed 400V.
A "real" EL34 should stand a Va of 2kV at zero plate current.

[tedmich]

John Chambers has made several monster amps with these http://www.chambonino.com/construct/const17.html

heres a design using 20 of the big bottles, he has another with just 8 807s. He graduated to 813 for bigger power ; )

[Mick Bailey]

Monster? I'll say. That's some dedication.

The one thing about 807s is where else would you get a decent 'golden age' tube suitable for decent audio at such a low price?

[Gingertube]

The 807 Application Report.
https://www.tubezone.net/pdf/807stc.pdf

I had a recollection that Standal did an 807 Amp that was used by Chet Atkins but cant seem to find a schematic for it.

Have a box of 12 NIB Amperex 807 with ceramic bases (the high altitude use ones for B52 Bomber Servo Amps).

Cheers
Ian

[Mick Bailey]

I also have some Cossor ceramic base 807s- I wondered what they were used for.

[x-pro]

http://tubes.tw/shop/product_info.ph...5srci87h692fr3

[Mick Bailey]

Thanks for the link, and look at that price. I always though of these as cheap tube - I paid £0.50 or about $0.80 at the time about 15 years ago because nobody wanted them.

[tedmich]

Pete Millett also has a 807 design, not for guitar of course, but his site (pmillett.com) seems to have issues currently.

[tedmich]

this article has some good info too!

[Mick Bailey]

Nice reading. I'll print this out for an afternoon armchair read with a glass of Scotch. Much better than reading off a screen. One of the things I like about 807s is the steampunk look with their anode caps when they're on display.

[Chuck H]

Nice reading. I'll print this out for an afternoon armchair read with a glass of Scotch. Much better than reading off a screen. One of the things I like about 807s is the steampunk look with their anode caps when they're on display.

Well that kind the thing, isn't it? They deliver the goods AND the "look". It wouldn't matter if they didn't deliver the goods though. That's why it's an enduring tube.

[soundmasterg]

Not to aside the thread, but...

Looking into alternative power tubes has me thinking it might be fun to make a 50W Champ type amp with an 813 power tube

EDIT: You could probably drive it with a parallel 12au7 or, if necessary a 6v6. This would, of course, be strictly a "because I can" project. Way on the back burner but I look foreword to any commentary

My grandpa was a ham radio guy and he used 813's quite a lot. I inherited his stuff, which included some ham radio thing he was building that was supposed to use a pair of 813's with 2000V on the anodes! I seem to recall from reading somewhere that to run a couple 813's with 2000V anode volts for audio power you would need a 6L6 to drive it, but you could get 500W out of a pair. Sounds to me like it would make a good bass amp!

I've never had the time to do anything with these 813's I have but maybe once of these days. Of course at those voltages any chassis would need interlocks that would shut off the high B+ if opened and other safety considerations. Also I have no idea where to source an appropriate transformer pair, and 813's are HUGE too, so you would have to have a really big chassis and cabinet to house them.

Greg

[Pixel]

Fred Nachbaur's Dogzilla puts out over 200 watts through a six-pack of 807s.