+275V reading

[atul.mehta6]

Hello,

My mainline was working well till today morning. Unfortunately the exhaust tip of one of the 6C45PI tubes broke. Fortunately I had a replacement tube around.. I re-did the measurements again after putting in the new tube. The voltages seem to be in spec except for the +275V reading and the IA on both boards. They both show ~262.8 VDC. Should I be worried? (My input line voltage is ~120V). While the diff is only < 5% if there is something I can do to get closer to spec... I would appreciate a few pointers...

Also I noticed that biasing for the new tube seems more difficult. The voltage will drop to 144V in less than 1/2 hour. I am assuming that this might be because the new tube might need to cook in for a little bit.. Any idea on how long that might possibly take..

Thanks in advance!

 

[Paul Joppa]

No worries; the 275v should be within 10% or so, but anything from 235 to 305 will work just fine - the shunt regulator isolates it from the actual audio circuit. (And the regulated 225v is further isolated from the 6C45P plate by the current-source plate load.)

The 145v at the plate can vary 5% or so with no real problem. It will drift a bit as the 2N2222A warms up even if the 6C45P is fully broken in.