High B+ at 117 line voltage, Bad rectifier?

I have a ST70 with the VTA driver board (3 ea. 12AU7's). Getting bad distortion at moderate listening levels. Checked the B+ at the board and it's 425V even at 117V line voltage using a variac.

At the rectifier (JJ GZ34S) I get 389 VAC. At the 40uf lug its 479. After the choke its 476. The choke checks out at 61.6 ohms. Book says 62. But why only 3V voltage drop? KT77 tubes are biased at 45ma as measured across 10 ohm resistors, so 45mv. B+ to the board is 425. If I lower the line voltage to obtain 385 to the board then I'm at around 102 V. IT sounds better until the volume is up then distortion again. I suspect its from low filament voltage due to low line voltage.

Could it be a defective rectifier tube? I only have the one. I guess I may need to buy another to compare.

-Mark

45ma through a 10 Ohm resistor would give 450mv, not 45mv. Was that just a typo?

If you really have only 45mv the tubes are barely on, which would definitely cause distortion. Would also explain the high B+ and why only 3v is dropped across the 62 Ohm choke (48ma total current).

If that is the case all you need to do is turn up the bias on all 4 power tubes to 45ma (450mv) to fix it.

LOL, I can’t read my own meter. I read .40 v in the installation instructions and my brain said 40 mv, not 400. Sorry for wasting you’re time and mine.
I can’t follow simple instructions.

No prob. Glad to help. Made the exact same mistake myself once.