Is anyone usig 807s?

[Mick Bailey]

I've built a few hi-fi amps with 807s and they work really well for a clean amp with plenty of headroom. Is anyone using them in guitar amps? The only real downside I've found when using them is the screen voltage limit.

[Helmholtz]

What is your reason the prefer 807s over 6L6GCs?

I have a quad of QE 06/50s but haven't decided yet what do to.

Where do yo find insulated anode caps?

[Mick Bailey]

The 807 will withstand much higher plate voltage, which is good if you have a mains transformer with a secondary voltage that's much too high for a 6L6GC. The 807 is rated for 600v but I've found the Osram ones run up to 1kv so long as the current is limited .Ceramic anode caps came from Bel Tubes.

I quite like the look of them for hi-fi - here's a build I did for a customer, though running at a sensible voltage.

[Chuck H]

That's real pretty. But I only see one transformer.?.

I also like the way the anode caps and Coke bottle tubes look. It leans really retro. Like you need one of those huge blade switches with a wooden handle that makes a SHUCLUNK! sound when you toss it. Arching a little with blue sparks as it nears the on position. Muwahahahaha!!!

[Mick Bailey]

Thanks. The output transformers and choke are on the inside to reduce coupling, plus they would have needed covers and by the time I'd struggled to form the 1.8mm stainless chassis I'd had enough with the metalwork. A guitar amp with 4x807s in a row that you could see would look really interesting and unusual.

The 807 used to be really cheap. I have a stash of NOS ex-WW2 stock that cost £0.50 (probably 70 cents at the time) each about 15 years ago. Maybe the military set a tight spec as the matching between different examples is very close - much tighter than other tubes I've encountered. Another plus is they're far more rugged than a 6L6GC - the internal supports and construction is more rigid. They also exhibit little or no microphonics. Given that they were a transmitting tube extensively used by the military they probably had to deal with more shock/vibration in portable or mobile equipment.

[Chuck H]

They're still a lot cheaper than the common big bottle tubes. I guess my only major reservation using them for guitar amps would be the anode cap design. Fine for a personal build done by someone that knows the dangers but I would never hand an amp over to a "guitar player" where high voltage could be accessed from outside the chassis. The screen voltage limitation is a minor issue for the most part. Though it does need an extra circuit consideration. Another more minor consideration for me would be whether or not I could always get them. Once you've troubled to use the right sockets and anode caps and designed the power supply for the right screen considerations it would be a real let down and some work to retrofit for a modern tube type. I also noticed in the data sheets that example circuit RA varies widely with voltage compared to tubes I'm more familiar with. I'm not technical enough to know why or what it might mean for a guitar amp design.

[Helmholtz]

Thanks. The output transformers and choke are on the inside to reduce coupling,
.

Is your stainless chassis ferromagnetic, i.e. does a magnet attach?
Common stainless steel types often are non-magnetic, so don't shield against magnetic fields.

[Mick Bailey]

That one is magnetic. I don't know the grade - it was an unmarked sheet I had in stock for a good number of years and was a real challenge to bend and I should have annealed it along the bend lines first. My DIY folding machine will bend just over 90 degrees in 2mm aluminium, but this sprang right back to around 60 degrees.

[Leo_Gnardo]

For what it's worth, around 15 years ago I worked on a little boo-teeky combo amp that used a pair of 807's in the output. As-is the little thing put out a pretty good holler in terms of volume & penetration but was by no means anywhere near the 100 watt monster its owner thought it should be. Somehow in the sales blarney, the tale of some enterprising ham radio speed demons was related: in a radio transmitter they submerged a pair of 807's in a pot of transformer oil and could measure 100 watts, so there's the source of antsy owner wondering "where's the BEEF?" Well, given the puny power supply that was adequate for a small amp sporting a pair of 6V6's, the best it could do was maybe 9 watts of honest clean power just prior to clipping. Once the truth was known owner settled down to enjoy his expensive prize, plus probable near infinite lifetime of his super tough output tubes performing in a low demand circuit where they could laze along for many a decade. In terms of tone, for all that I heard nothing special to attract me to build guitar amps with 807's.

[Chuck H]

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

[Mick Bailey]

The high outputs associated with the 807 in transmitting use lead some builders to think they can get the same figures in audio applications. They're often configured as an HF oscillator in Class C for transmitting, with an optimised tuned load at a fixed frequency.

I've considered the 813 a few times, but never found them at a price where I could happily put them back in the drawer if I didn't like the results.

[Leo_Gnardo]

it might be fun to make a 50W Champ type amp with an 813 power tube. 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

Had a crustomer maybe 15 years back ask what about building a consummate combo amp with a mighty 300B to drive the output. I guided him away from the "because I can" frame of mind back to relative sanity. I should get psychologist pay. I think since then he's stuck to his trusty Vibrolux Reverb, good lad!

[Chuck H]

Had a crustomer maybe 15 years back ask what about building a consummate combo amp with a mighty 300B to drive the output. I guided him away from the "because I can" frame of mind back to relative sanity. I should get psychologist pay. I think since then he's stuck to his trusty Vibrolux Reverb, good lad!

Ok... But that's your advice to a musician/crustomer. Best he just sticks to the most useful gear and makes music. But we're all nerds here. A 50W Champ doesn't mean the same thing thing in both worlds

No guitar player untrained in electronics would ever be left alone with it. Not with 1kV on an anode cap outside the chassis. I might as well just shoot the guy myself.

[Mick Bailey]

With an exposed anode cap you have to use a monitoring circuit to immediately disconnect the HT if the cap comes off, or a crowbar circuit that shorts the HT and blows the fuse. With 1Kv that becomes more problematic and my high-voltage 1kV+ hi-fi amp had to have a cover over the caps which rather spoiled the look.

[Chuck H]

I would never have an uninsulated anode cap for sure. But since it's pretty common for guitarists to mess with the tubes in their amps I can just imagine someone ham handedly pawing at the cap and perhaps lifting it just enough to expose some of the anode connection while the cap is still in contact with it. Fingers curled under the cap and potentially making contact. Or even poking a finger into the cap once it's removed. But I've never seen the physical arrangement for myself so I don't really know if any of that is possible. I only know that most guitar players only become cautious when a chassis is opened up but seem to feel free to mess with the tubes.

One could probably arrange something custom so that the caps were mounted on a hard conduit that disconnects from a HV plug in the chassis simultaneous with the anode cap. But this is all just speculation now. Back to the 807's...

Looking at your build and the specs of the 807's has me considering them for a hi fi build I've been planning. Market prices seem to be about $25-$35 USD per tube NOS. And looking around I see that Sino (the old Shuguang people) made a modern equivalent though I don't know if they still do. It was somewhat more expensive but not so much as EL34's or 6L6/5881 types. Making it an attractive option for a guitar amp build. Who wouldn't want good tubes for less money. Especially with the recent price increases.