7 pin power tube

[lowell]

Working on a single ended amp that has 1 7-pin tube (about the size of an el84) which is transformer coupled. The PLATE is pin 7. I'm having a tough time figuring out what it is. Its not an EF86 EF98, or 6au6. The tube has no markings on it and I've looked very closely under good light.

Edit: The screen is 6 and plate is 7.
Also of note. The tone circuit is a cap and 20k POT between plate and screen. Very cool take on a tone control utilizing neg fb. Very weird that they chose to have 130vDC on that pot. I think I'll fix that and add another cap. This amp sounds INCREDIBLE. It's a Gregory Mark 6 and I couldnt find much if any info about it online.

[Enzo]

Hard to say, who made the amp? Any model name or number?

50C5? Is there a power transformer? Are the heaters wired in series or is there 6v parallel throughout? What is the rectifier tube? 35W4?

[lowell]

Sorry please see my edits. The heaters are in series. The rectifier is indeed a 35W4. First thing I did to it was install an iso PT

[lowell]

Yep a 50C5! Just like a Sears Intercom schem I found.

[drewl]

What did you use for an Iso PT?

I may have to install one in a B&H projector amp but I'm trying to convince the owner that it's not worth the trouble.

[lowell]

Triad 68x I believe...from Mouser.

Thanks Enzo

[drewl]

Cool thanks.

[lowell]

Back home now.

http://www.mouser.com/Search/m_Produ...L8G7F80A%3D%3D

[nosaj]

Back home now.

http://www.mouser.com/Search/m_Produ...L8G7F80A%3D%3D

How about a pic and the schematic you found?

Thanks,
nosaj

[lowell]

When I said "just like" I meant in regards to exact same tubes. The circuit is quite different.