Posted by Torfinn (A) on August 15, 2004 at 13:22:51

I have just finished building the Joplin and I would first of all thank Brian for the the very impressive building manual.
Good work!

When I measures the voltages I get voltages thatis not exactly the same as the manual says:
B+ = 330V (manual says 290-320V)(no tubes installed)
With all tubes installed the values go down to about 300V.
Pin 1 and 6 ECC81(12AT7) = 59V (manual says 70V)(small tubes installed)
With all tubes installed the values go down to about 53V.
Pin 1 5687 = 220V (manual says 170V)(small tubes installed)
With all tubes installed the values go down to about 200V.
Do this measurments tell me that there is something wrong with the amp or should I adjust the values by changing some resistors?

Regarding the other adjustments it certainly looks like the amp are working fine and I get the hum down to 2mV which I guess are not too bad.

And the amp sounds great :-)
I do get noise when I use the internal volume control and guess that it has something to do with the grounding of the volume pot, but when I turn the volume all the way up and use an active preamp there is no noise.