Stereomour in Burbank...Voltage Question

[ODYOFAEL]

I have just finished assembling my Stereomour. I have one question about the voltage reading. I took a picture of the sheet of paper so it would be clearer. I have attached pictures of the amp as well.
Regarding the low voltage reading...is this bad? Everything else is almost spot on. Also, I am driving a pair of Omega Super 3T speakers (94 db) and and is it normal that I am already at 3 o'clock volume position to reach normal listening level? My room is 10 x 12? Or is the low gain caused by the voltage I am getting at those terminals (2,14,OA and OB)? What could be the cause? Thanks in advance.

 

[Paul Birkeland]

Wow, this is actually a very interesting post.  If I had to make a guess about what's going on with your amp, I'd say that you have a 12AT7 that isn't quite a 12AT7.  With all other voltage spot on, the drop in voltage could equate to a tube with higher gain, and the volume control position is a possible indicator of this problem.

In terms of what this tube actually is, it's possible that it's a 12AX7 variant (7025 comes to mind).  More on relabeling can be found here:

http://www.vacuumtubesinc.com/VacuumTubesHallofShame.aspx

There isn't any harm to the amp to leave this tube in, but I'd e-mail Eileen about getting a replacement tube (queen ( at ) bottlehead (dot) com )

-PB

PS - your amp looks great, did you end up masking the plate chokes or painting the whole thing?

 

[ODYOFAEL]

Wow, this is actually a very interesting post.  If I had to make a guess about what's going on with your amp, I'd say that you have a 12AT7 that isn't quite a 12AT7.  With all other voltage spot on, the drop in voltage could equate to a tube with higher gain, and the volume control position is a possible indicator of this problem.

In terms of what this tube actually is, it's possible that it's a 12AX7 variant (7025 comes to mind).  More on relabeling can be found here:

http://www.vacuumtubesinc.com/VacuumTubesHallofShame.aspx

There isn't any harm to the amp to leave this tube in, but I'd e-mail Eileen about getting a replacement tube (queen ( at ) bottlehead (dot) com )

-PB

PS - your amp looks great, did you end up masking the plate chokes or painting the whole thing?

Thanks! Yes I did tape the OT. I was going to revove the cover but...=)  It turned out nice though.

Re: the voltage. I did re-check and they are almost spot on. Terminal 1,15,A2 and C2 getting around 380 though. Is that withing limits?

 

[Paul Joppa]

I suspect it's actually a 12AU7. Can you read the marking on the tube? 90-92v would be right on the nominal value for a 12AU7 at that operating point.

 

[Paul Birkeland]

It would be good to double check the Kreg voltages, just to be sure.

That tube sure doesn't look like a 12AU7.

 

[ODYOFAEL]

I swapped the unmarked tube (12AT7) that came with the kit with a 12AT7 Telefunken (also tried an RCA) and guess what, what used to be 92 volts went up to 230V. Sweet! Now at around 1 oclock volume, I am at my normal listening level. Thanks guys. I have called Bottlehead today and told them about it. The tube is on it's way.