1974 Model T with no sound

[2000s a space odyssey]

Ok here is the run down.  Saturday night at the gig doing a sound check everything worked fine.  Switched the amp onto standby.  Showtime 30 minutes later and the amp won't produce a signal out to the speakers.  Went through all possible eliminations and it's the amplifier. The tubes look ok and you can hear the amp hum when you switch it off of standby.  Touching the guitar cable tip but no sound.  This is a second generation Model T with the mid select switch.  Its a silver logo and knobs though.  All original tubes and capacitors.  Help me trouble shoot this and or recommend me a tech.  I live in southcentral Pennsylvania.

[loudthud]

Set the amp up in a quiet room. Connect a speaker and turn the amp on and let it warm up. Turn the Master Volume to zero. Turn the Standby on. Listen closely to the noise from the speaker. Rotate the Presence control form zero to ten. Any change in the sound from the speaker? There should be more hiss as you turn up the Presence.

Turn up the Master Volume and set the channel Volumes to zero. Do the Treble Mid and Bass controls change the hiss and/or hum? Now turn up the channel Volumes. Do they change the hiss and/or hum?

[Isaac]

IIRC, my 2G T did a similar thing a while back. Cycling the standby switch usually got it back. Sometimes a full shutdown was required. It doesn't do it anymore.