Sencore MU-150 GM Pot - Page 1
Forum section: electronics / testgear

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: November 30, 2022, 12:18:44 am
content: Can anyone help me understand why the GM pot R20 which is a wirewound go open?]I can show a photo of the break if necessary.The break is in the 50K not the 5K section.Ganged together and not a standard of mfg. it's unobtanium.I can get separate wirewound pots but not ganged.So the main question being, in the circuit provided in jpg or pdf (page 13) what is the reason for a wirewound pot?I don't see any current or voltage issuesI await your feedback to help me understand as to why a 2W pot is used.https://bama.edebris.com/download/sencore/mu150/MU150%20Service%20Manual.pdfedited for all the placed in my text. This happens every time I post.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 30, 2022, 01:56:56 am
content: maybe an mechanical stresscan you show a picture of the pot ??Unless the circuit as high voltage passing thru it, a carbon based potentiometer woud fry ??In the past i did make some fit of dual gang pots, IE: same series body, and switch one of them to fit the needs in audio stuffexample: with some pliers / cutters slowly unbend the case pins, remove one stage and switch it for another value but having the same body ??the second image are 2watts dual gang potentiometers, the same trick could be usedEDIT: oh i remembered, in the past some of theses pots since they where wirewounded had a "somekind of a notch feeling" when you passed on the wirewound, does your's do thatLike a variac transformer, you sense the wirewound as you turn ??

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: November 30, 2022, 02:09:08 am
content: It's late.I did say (I think) that that's how I knew there was damage and I would take a photo, and your photos can't be bought.Yes I do know how to cobble together pots.Tomorrow there will be a photo........

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: November 30, 2022, 02:50:25 pm
content: The original pot when actuated would take the meter, a 90° arc, from 0°-30°, then to 0 then to 60°-90°I already knew the about the strange double pot configuration years ago.I messed about with another 50K WW pot, but it is smaller in diameter.I'm going to have to do some mechanical work to bung it in the original back half. Something I don't want to do. AT ALL.I'll have to get creative with J-B Weld and metal. The worst part is the front shaft is too short. Enter a shaft coupler. I would not want to show what that all put together would look like.Anyway, getting back to the original question, I still need an opinion why the pot would burn.The appears to have no discernible current or HV to cause such a thing.Open for analysis and opinion.Here are the photos from this morning.They will show:1) The original unmarked (manufacturer) naked 50K pot.2) The full open original.3) The original pot wiper burn.4) The original back (5K) half with the possible complexity of the replacement conjoining.5) The original back (5K) half with the possible complexity of the replacement conjoining.6) The original back (5K) half with the possible complexity of the replacement conjoining.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 30, 2022, 03:51:38 pm
content: I know it's not fun but in the end if it still works okay, that's your rewardIt is still a good piece of instrument ...

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: December 02, 2022, 12:31:37 pm
content: Bueller?Doesn't anybody wish to offer a guess as to why a pot would burn up so with such low current - low voltage?