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Old 10th September 2011, 12:57 PM   #21
RJM1 is offline RJM1  United States
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Quote:
Originally Posted by SatinMill View Post
oh, and if anyone is curious this is the pot

original produced by alps

35001070 GTP-500II Volume Control Motorized 50KBx2 W/Motor

A modern clone I found, though I can't find any way to buy a single unit, just quantities of 1000.

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(request sheet)
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Old 10th September 2011, 01:25 PM   #22
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Ask for samples.
(request sheet)
Damn, I already asked if they'd be willing to sell one to an individual, I really should have thought to phrase it that way.

Oh well, if they're unwilling I'll ask again for a sample in a few weeks time with my partner's identity.
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Old 10th September 2011, 04:44 PM   #23
AndrewT is offline AndrewT  Scotland
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It has already been flagged up by at least two Members.
Check for DC across the pot and/or wiper.
Did the good/better channel have the same DC readings when you measured them?

If this persists you could blow your speaker.
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Old 10th September 2011, 04:59 PM   #24
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Something I saw at the Silicon Chip website... with the amp power off, connect a signal generator to the wiper and arm 1 of the pot. Connect a signal tracer to the wiper and arm 2. Move the wiper. If the noise is present it's caused by the pot.
That's my recollection. I can dig up the article if you'd like.
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Old 10th September 2011, 09:26 PM   #25
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Depends why the pot is scratchy. If due to dust then it needs spraying with contatc cleaner. If the pot track is worn out then no amount of spray will fix it and it needs replacing.
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Old 11th September 2011, 07:39 AM   #26
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Well, looking at a blowup of the link showing the pot, it does seem to be an ugly one to dissasemble. Looks like one channel in front of ganged wiper and second channel behind. Front resistive element faces back and one behind faces front. Front can be got at with just the four bent tabs. Getting full access to back resistive element looks ugly, but doable. Might just have to suck it up and do it.
Don't know of any cheap motorized pots. The ones that had the screws were certain versions of Allen-Bradleys. The best quality pots used to be made by spectrol. Vishay made the best resistive elements second to none, but they've now merged with ohmite and Dale. Not bad, just no longer guaranteed that it will be a Vishay element that you get.

A dual audio taper 50K motorized pot shouldn't be too hard to find, only finding the exact mounting form factor may be iffy. I'd still give dissasembly cleaning a shot.
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Old 11th September 2011, 09:41 AM   #27
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Look what I found!

Motor Driven, Dual Section 50K Pot
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Old 11th September 2011, 04:03 PM   #28
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Quote:
Originally Posted by thaumaturge View Post
Thanks for that! I bought two of them as they're so cheap. The shaft isn't splined but I'll either modify the knob or see if i can transfer the shaft from the old one.
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Old 12th September 2011, 02:25 AM   #29
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FYI for others; they've also got some 100k versions.
Doc
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Old 22nd September 2011, 02:26 PM   #30
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So, the replacement arrived, I popped it in, the problem persists.

What the hell!?

Annoyingly I destroyed the old pot as I was curious as to just how messed up inside it was, I found a bunch of crud and even a few small hairs in there.

At this point I'm getting really pissed off at this amplifier, I like the sound the thing makes, but this issue is incredibly aggravating.

The only thing I can think of trying next is replacing the 4.7uF caps someone earlier in the thread suggested?
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