12dw7/ecc832

[lowell]

Hey all,
I've got a concertina splitter here and when I put the 12dw7/ecc832 (JJ brand) in there my 330vdc supply drops to 100vdc on the plate. When I swap in a JJ 12ax7 the plate voltage rises a huge amount, up to 240vdc. Is this the nature of this tube type? I've tried 2 different brand new JJ ecc832 tubes with same result. Doesn't make sense to me why this is this way.

[defaced]

I'm not sure, but I would guess current draw. A DW7 is half AX7 and half an AU7. That AU7 can pull 5 to 10ma in a typical circuit as compared tot he 1ma of the AX7. Run 5 to 10ma through a B+ dropping resistor and the voltage will drop considerably compared to the same dropping resistor and a AX7. Take some voltage readings across to the plate and B+ dropping resistors to see if this holds water.

[lowell]

Mike,
You think the 12au7 half of the tubes affects the plate of the 12ax7 half? Pin1 is the plate of the 12ax7 and that's the side that is dropping all that voltage. Pin6 is actually much higher and seems to not drop nearly as much.

[Wakculloch]

Are you sure you aint got an ECC823?

[lowell]

yes! I checked that after I found out they made those.

[defaced]

Hmm, they should be completely independent, so it doesn't sound like current draw is the issue.

I have read recently that JJ's quality has been suffering. It may be possible you have bad DW7s. What does the DW7 do in a known good circuit like a simple gain stage?

[lowell]

well when I throw an ecc83 in there all seems fine. I don't have anymore new dw7 to sub... maybe will order more and send these back..?

[Enzo]

How about throw a 12AU7 in the socket and see if that side works the same. For this test, it doesn;t matter how the other side performs, does it? That would verify that a 12AU7 type triode will perform this way or not, and that ought to tell you if this behavior is your 12DW7 defective or if they all would work this way.

[lowell]

Well I looked on JJ's datasheet and in fact I've been wrong all along. The Ecc832 tube is a 12au7 THEN 12ax7. Pins 1,2,3 are 12au7, Pin 6,7,8 are the 12ax7. Duh, must've looked at another datasheet for a 12dw7 when should've looked at JJ's Ecc832 datasheet. Don't want to change my circuit so I'm gonna order some Ecc823 tubes.