6u11

[benoit]

A friend of mine has an old Stromberg Carlson Signet 22 that looks really cool. However I can't seem to find the 2nd stage/PI tube, a 6u11 anywhere. There's one site (world tube something) that seems to sell them but I can't find a lick of data on them except a site totally in german.

Does anyone know what the pinout is and what might be used as an equivalent?

[Firestorm]

Damn Compactrons! A tube with eleven elements has to be a triple-triode with an internal shield (3 trides, plus 1 heater, plus 1 shield equals 11). Radio Museum www.radiomuseum.org/tubes/tube_6u11.html says it's a close match for a 6C10.

[Phil_S]

Are you sure that tube number is right. Duncan's TDSL says it's a 4 pin triode with the cathode directly heated.

[benoit]

It's definitely at least a double triode, as its used for 2nd gain stage and PI. Its weird though because several sources say its a 6u11 but on the schematic I found it calls for a 6u8. Very confusing.

[benoit]

Schematic Here

This is the schematic that says it takes a 6u8, which AES sells for 6 bucks or something like that.

I'm going to recap and install a 3-connector power cable, as well as add quarter inch jacks for speaker and input. Depending on how Mike likes it we may turn it into something else. A couple people have reviewed the amp on harmony central and word is that it sounds similar to a Marshall 18watt but with a little more output and headroom.

[Firestorm]

Are you sure that tube number is right. Duncan's TDSL says it's a 4 pin triode with the cathode directly heated.

That's a Mazda tube -- different numbering system. Annoying, isn't it? No wonder the tube industry is dead!

[Firestorm]

It's definitely at least a double triode, as its used for 2nd gain stage and PI. Its weird though because several sources say its a 6u11 but on the schematic I found it calls for a 6u8. Very confusing.

Gibson and Ampeg changed circuits a dozen times before updating a model # or name. Swedes can be just as stubborn. Just check the layout -- if it's a triple-triode, two triodes will be wired as a Schmitt or a long-tailed pair -- you'll spot that -- and the other will be a preamp section. The 6u8 in the schematic will only have two sections -- maybe 6u11 is a later design from a split load inverter to a Schmitt.
It's got to be pretty clear from how it's wired.

[benoit]

It's definitely at least a double triode, as its used for 2nd gain stage and PI. Its weird though because several sources say its a 6u11 but on the schematic I found it calls for a 6u8. Very confusing.

Gibson and Ampeg changed circuits a dozen times before updating a model # or name. Swedes can be just as stubborn. Just check the layout -- if it's a triple-triode, two triodes will be wired as a Schmitt or a long-tailed pair -- you'll spot that -- and the other will be a preamp section. The 6u8 in the schematic will only have two sections -- maybe 6u11 is a later design from a split load inverter to a Schmitt.
It's got to be pretty clear from how it's wired.

You're right about that, certainly. Hopefully he'll get that thing to me soon so I can actually take a look. I have yet to see anything but pictures of other Signet 22s on the web.

[Firestorm]

Fender used a 6C10 in the "Super Champ" and some other amps from that era. The Super Champ used it in a splt load inverter, but I'm sure I've seen it used other ways.
Ampeg got on the Compactron boat before Fender did -- ANYBODY HAVE THOSE NASTY OLD 6BK11's YOU WANT TO GET RID OF? -- but they're all a PITA to deal with if you can't get a NOS tube.
If that 6U1 1is still good, you're fine! (but please tell us what resistors and caps were attached to where).
If it's shot, try the 6C10, or add 9-pin sockets and replace it with modern tubes (your friend will have to eventually).
My guess: treat the 6U11 as if it were 1 1/2 12AX7 -- three triodes of 100 mu each. Good luck!

[VacuumVoodoo]

6U8 = 7687 = ECF82 triode + pentode in one bottle. ECF82 are plentiful and cheap.

[Firestorm]

There's at least one guy on Harmony Central who thinks his Signet 22 has a Compactron with a pentode section (the 6u8 is assume). If that's true, what kind of phase inverter is that amp using? Probably the only thing to do is look at the beast and see how the tube is wired.

[benoit]

Oh boy.. new wrinkle. Mike just called and told me that it's not a signet 22, its a signet 70. Very strange.. Can't find reference of it online. All bets are off until I actually see this thing.