5f2a Hum in standby ( resolved )

[makingnoise88]

Hello Gents!

I just finished another 5f2A using the hoffman board but it was a scratch build.
I'm using a 3 position switch that Ive used in other builds for OFF, STANDBY, ON works great.
The problem is when I turn the amp on standby there is a hum coming through the speakers.
When I flip it on to play the amp is dead silent and sounds great. When I switch it back to stand by from play the HUM is WAY Louder but quiets down as the tubes drain.

All of my heater lines are twisted and in the back of the chassis, Ive chop sticked the amp, and I don't see anything out of place. So could you give me something else to try and look at?
Thanks for the help!

[sluckey]

I suspect the standby side of the switch is wired wrong. I suspect you have the OT red lead connected directly to the rectifier socket as shown in Hoffman's layout but you connected the stby switch in the line headed to the board. This leaves B+ connected to the OT all the time but when in stby mode the filter caps are disconnected. This will result in some pretty big hum.

If this is the case, move the OT red lead to the board so that the stby switch will also kill B+ to the OT.

[makingnoise88]

Stuckey, you were right as always! 
Gosh thank you so much!

[Crate50watt]

I posted a thread last night because I have excessive noise in an 18w tmb I just finished. I am now suspecting that  I may have the same problem with some serious hum. My ot primary is connected directly to my b+ filter cap. Should I move that to the board? To me, electrically at least, it would seem that it wouldn't make a difference? I didn't install a standby switch, and I think from now on I am going to put one in every amp...

[sluckey]

Since you have no standby switch you cannot have the same problem.