Classic Hifi Care

Ok to preface, lot going on in my life so maybe taking it a little too much to heart.

So, about 2-3 years ago my SHF 4 started to hum very loud, so I knew it was time to recap the amp (I picked it up 3 years before as someone's daily driver, with a VoM turntable switched in, an so just used it on occasion). I switched it out and thought I could re-cap when I could, which was around the start of this January! So, pulled the paper, and stuffed the electrolytics, got sidetracked for a couple of weeks and replaced the last 3 capacitors this afternoon, and cleaned up the tube sockets. Reinstalled the amp back in the cabinet, hooked everything back up and turned it on and got the hum, but even worse.
I felt like a total failure. I have been doing this for over 15 years, I go cap by cap and I am not sure where I could have slipped up.
Any ideas what might be the problem? I'm going to pull it and go back over my soldering, but could it possibly be something else? I would appreciate any thoughts.

Additional info: Hum is there no matter the volume, whether the tuner is connected, and no matter the selector position. Tuner produces signal thru hum, but is very distorted.

Thanks!

Inspect carefully for stray clippings from leads, solder blobs making contact. You said "stuffed electrolytics"--like refilled the can? Then check for adequate insulation. You said "pulled paper"-- replaced paper caps? Get out your schematic and make sure you attached to appropriate points at each end. Maybe do a tube check, in case one of them failed from handling?

Chris Campbell

It's good to see you on the forum! Sorry about life "getting in the way of progress". I know how that works, trust me.

My suggestion is to recheck the connections of the filter caps you replaced. It's really easy to get one installed incorrectly. Been there, done that, everybody has. If you determine that the caps are okay, start pulling tubes, start closest to the input and see if maybe you have a cathode to heater short in a tube. If you pull the tube and the hum changes or quits, sub that tube. IF it's in the power supply, the hum will stay there until you pull the last tube.

Could be a tube with heater-cathode short.

Conelrad

electra225 wrote: ↑Sun Feb 15, 2026 12:01 am It's good to see you on the forum! Sorry about life "getting in the way of progress". I know how that works, trust me.

My suggestion is to recheck the connections of the filter caps you replaced. It's really easy to get one installed incorrectly. Been there, done that, everybody has. If you determine that the caps are okay, start pulling tubes, start closest to the input and see if maybe you have a cathode to heater short in a tube. If you pull the tube and the hum changes or quits, sub that tube. IF it's in the power supply, the hum will stay there until you pull the last tube.

On another list, it was suggested to pull all tubes but the outputs and the rectifier, and if it still hums, it is most likely the electrolytics. I may follow it up with your suggestion just to further narrow it down. Thanks!

Pulling all the tubes but the rectifier and outputs won't cover all the bases. In this case, after you have replaced the filter caps, the hum should have been eliminated if the caps were the problem, if the caps are good, and if they are installed correctly. Since you still have the hum, seems like either that wasn't the problem, it wasn't the ENTIRE problem, or you have two problems causing the hum. Pulling the tubes, one at a time, will let you know if you have a cathode to heater short. Good luck.....