2009 Blues Deluxe Uncontrolled Hum

[Daves in texas]

I have a 2009 Fender Blues Deluxe and it has a tremendous Hum issue. The second I turn the amp on with standby off there is a giant Hum! Can’t control it with Master or Channel volumes.
I have replaced all the Major Radial caps on the board. And the 4 Axial Power Caps as well. Also I have switched the tubes totally and using a full set of tested tubes. I’ve measured the major resistors they are ok as well. All the ribbons are good. Fuse and power good. I can’t get to the test points since I can’t get the power over 30 volts. The amp jacks are good and the speaker jack is correct and good. Tested the power tubes before this Hum stated they tested at 26 mili amps.
This is the same amp model with the cut C53 Trace to R52 which is a simple metal jumper.
Also I have put the amp back into its original condition by removing a jumper resistor on R9 and C36. Used jumper wire to reconnect C53 with R52 wire and then the 240r resistor as per the parts list. No good. No matter what I’ve tried is working. Still exactly on power up there’s that uncontrolled Hum. Any ideas I’d sure appreciate the help.

[Enzo]

I can’t get to the test points since I can’t get the power over 30 volts.

Whoa! What do you mean can't get over 30 volts? Are you trying to run this on a dialed down variac or something? Are you using a bub limiter that is glowing bright and 30v is what is left at the amp?

Voltage readings in the circuit are meaningless if the amp doesn't have 120v mains power - or 240 around the world. With standby off there is no B+ in the circuits, so hard to think right away how it makes noise in the speaker. And whatever the 30v limit means, WHY can you not get past it?

Now if standby is ON, then the B+ is live and then my first suspect is a shorted flyback diode on the power tube board. D4 or D5. And way less likely, but a short from primary to frame or primary to secondary on the output transformer.

Disconnect the brown and blue wires from the OT to the tube board, still hum? If not, check those diodes. If it still hums then also disconnect the red CT wire. if that stops the hum, we have transformer trouble.

[The Dude]

Also, check solder on the output tube sockets. It's a common problem in these amps- common enough that I just always/automatically resolder them when one of these comes into the shop.