Surging hum followed by crackle, then repeats - both channels

Hi All,

I'm new to the forum, and look forward to joining the community.

I'd like to ask the group's opinion on this situation with my late 50s/early 60s ST70. It makes a humming sound that surges and stops with a crackle/thump, then repeats over and over. (I recorded the sound, but since I'm a new user, I can't post a link to it here for 7 days.)

The caps are relatively recent - 10 years or so (they're not original).

The tubes don't have much listening time on them - less than 100 hours, I'd guess.

What kind of problem does this sound like to you? Thank you for your guidance!

Ron

You can find a good troubleshooting guide here:
https://dynacotubeaudio.forumotion.com/t274-quick-troubleshooting-guide-for-dynaco-tube-amps

Thanks, Dan - I'll get to work!

Looks like the 7199s are dead, the rectifier tube is iffy, and the quad cap is bad. Thanks for sending me in the right direction, Dan.

Question for you: what is the current thinking about the dependability of new quad caps? I'm wondering if I should try a new one or replace the can with a more modern module.

Again, thank you.