Now that I have your attention. LOL I've been working on a Belmont 602B Freshman and it works great with the top off but when I put the top on (cabinet) it hums. Already tried goat shields but didn't ground them to the chassis. I know it is noise but having trouble correcting this problem. Anybody out there in radio land run into this problem? Thanks George T.

:Now that I have your attention. LOL I've been working on a Belmont 602B Freshman and it works great with the top off but when I put the top on (cabinet) it hums. Already tried goat shields but didn't ground them to the chassis. I know it is noise but having trouble correcting this problem. Anybody out there in radio land run into this problem? Thanks George T.

Try it with the tube shields grounded to chassis. Sometimes to leave the shield float like that may pick up hum. Also check if the cabinet is isolated from the chassis, and may even have a capacitor from chassis to cabinet.

::Now that I have your attention. LOL I've been working on a Belmont 602B Freshman and it works great with the top off but when I put the top on (cabinet) it hums. Already tried goat shields but didn't ground them to the chassis. I know it is noise but having trouble correcting this problem. Anybody out there in radio land run into this problem? Thanks George T.
:
: Try it with the tube shields grounded to chassis. Sometimes to leave the shield float like that may pick up hum. Also check if the cabinet is isolated from the chassis, and may even have a capacitor from chassis to cabinet.
:
: Well I have tried pretty much everything with no luck. I'm kind of wondering if the speaker cloth might be causing it. The speaker cloth has what looks to be metal thread woven into it (gold). I sure would hate to take it all off and still have the problem. With the chassis playing with out the cabinet on it, it sounds fine but as you lower the cabinet onto the radio the hum gets louder. Weird!!!! Any ideas would be really welcome at this point. When you turn up the volume it covers up the hum. Thanks again, George.

Hi George

Sometimes the hum is there even outside the cabinet but not noticed. Putting a speaker in the cabinet can improve low frequency response

Try increasing electrolytic filter capacity to see if there is improvment.

Norm

:::Now that I have your attention. LOL I've been working on a Belmont 602B Freshman and it works great with the top off but when I put the top on (cabinet) it hums. Already tried goat shields but didn't ground them to the chassis. I know it is noise but having trouble correcting this problem. Anybody out there in radio land run into this problem? Thanks George T.
::
:: Try it with the tube shields grounded to chassis. Sometimes to leave the shield float like that may pick up hum. Also check if the cabinet is isolated from the chassis, and may even have a capacitor from chassis to cabinet.
::
:: Well I have tried pretty much everything with no luck. I'm kind of wondering if the speaker cloth might be causing it. The speaker cloth has what looks to be metal thread woven into it (gold). I sure would hate to take it all off and still have the problem. With the chassis playing with out the cabinet on it, it sounds fine but as you lower the cabinet onto the radio the hum gets louder. Weird!!!! Any ideas would be really welcome at this point. When you turn up the volume it covers up the hum. Thanks again, George.

Thank you both, put in higher value Electrolytic Caps and it reduced the hum a lot. Still have it though but it isn't bad enough to worry about. I think when you put the case on it it amplifies the sound and brings out the hum more accoustics maybe. I believe there is a bad resistor that is changing value when it heats up. The volume changes from good volume to lower volume then it comes back up to normal after 5 or so minutes and plays fine after that. Already changed the tubes out and they didn't make a difference. Maybe after I get it to stablize I'll loose the hum all together. One can only hope. Thanks, George T

Out of curiosity what values did you change from and to? Thanks

Thank you both, put in higher value Electrolytic Caps and it reduced the hum a lot. Still have it though but it isn't bad enough to worry about. I think when you put the case on it it amplifies the sound and brings out the hum more accoustics maybe. I believe there is a bad resistor that is changing value when it heats up. The volume changes from good volume to lower volume then it comes back up to normal after 5 or so minutes and plays fine after that. Already changed the tubes out and they didn't make a difference. Maybe after I get it to stablize I'll loose the hum all together. One can only hope. Thanks, George T

Hi JF's, I have heard you can increase them up to 80% but have worked on radios that had them much higher. I just replaced 3 electrolytics in a radio and they had a 100uf in place of what should have been a 30uf. It worked fine with the 100uf and now with the 30uf. In the Freshman I raised the 20uf to a 33uf and the 5uf to a 10uf. It really helped a lot. Best 2 U