And now a voltage problem

[smithanh]

Checking voltage readings and got this:

Terminal.   Reading.  Printed
T1.               375.        350
T2.               140.        230
T14.             194.        230
T15.             375.        350
A2.               375.        340
C2.               375.        340
OA.              140.        230
OB.              194.        230

Everything else measured fine, and I'm not too concerned about T1, T15, A2, or C2  Since I just finished buliding the kit, and since I didn't see any sparks or smoke, I plugged it into my LaScalas and the sound is gorgeous, but the other bad voltage readings are like a mild toothache. Any suggestions?

[Paul Joppa]

The 375v instead of 350v indicates your power linevoltage is a bit higher than that at Bottlehead's lab. Actually, the design value is 360v. Not a problem as long as it's between 330v and 400v.

The 230v is at the plate of the driver; the design value is actually 200v (you can see this on the circuit diagram in the manual). It is more variable than the usual +/-15% due to the fixed bias of the driver. A lower voltage indicates a higher than average emission of the driver. It will drift up as the tubes age, but as long as it's less than 300v the tube is able to drive the 2A3 or 45. Your difference (140v and 194v) indicates some difference between the two triodes. In general I don't think this is important but you can experiment with matched-section premium tubes which should show more closely-matched voltages. As always, if you do experiment, please post your results!

[smithanh]

That's for the the reassurance. I've been listening for the past 4 hours and it sounds very good, getting better as it breaks in. Would it be worthwhile pulling the tubes and resetting them? I read on another post that might clean up some of the voltage differential. My bigger concern was that I might be causing some damage to components.

This was the first piece of any kind of electronics I've ever built and I want to complement and thank you for the attention to detail in the design and the instructions. I have no background in electronics (hell, I'm a political science professor!), but was able to put this together with a only few minor problems (all my fault for not reading the manual carefully and having no experience). And I especially appreciate that you follow posts from folks like me and respond to them so quickly. I look forward to listening to the Stereomour and am now angling to get a phono stage kit past my wife!

Thanks again,
Andy Smith

[smithanh]

Will send a picture of the finished project when I get to another computer ... no changes from the kit, but I'm rather proud of myself for putting it together without killing myself, and that my wife says she'll put up with the "ugly" (can you believe it?) LaScalas since they're paired with the Stereomour.