Stuck switch on Pultec Filter

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aprats

Member
Joined
Jun 24, 2021
Messages
7
Location
San Francisco, CA
Long time lurker, first time poster. Really appreciate the help you’ve all provided over the years!

I recently picked up a stereo Pultec filter, HLF-23C, which is essentially two HLF-3C’s in a single box. 3 of the 4 centralab switches turn beautifully. One is completely jammed / stuck. Any wisdom to share on the best way to get that switch moving again?
 
..most often grease around shaft bushing has hardened and is stuck. If metal shaft, take off knob, heat the shaft a bit with solder iron, get it turning with pliers. Keep moving while cooling down. Perhaps try to flow a bit of oil in there..
 
Thank you, Jakob.

Following up on this thread, I tried heating the shaft and turning with pliers, but the stubborn switch wouldn't budge. A little protected spritz of non-chlorinated brake cleaner did the trick. I then flowed in some oil and now all the switches are buttery smooth.

Spent the past couple days giving this guy a good scrub down and now it's ready for action.
 

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I just did a service on an HLF3 to bring life back to noisy intermittent switches - it’s amazing they are just popping up out of the woodwork. Does anyone know where to get a new front panel? This one has all the blue paint bubbling away at one end.
 
Thank you, Jakob.

Following up on this thread, I tried heating the shaft and turning with pliers, but the stubborn switch wouldn't budge. A little protected spritz of non-chlorinated brake cleaner did the trick. I then flowed in some oil and now all the switches are buttery smooth.

Spent the past couple days giving this guy a good scrub down and now it's ready for action.
Those old greases can go hard and oils turn to glue. I’ve had luck using freeze spray which shrinks the shaft inside the bearing and also cracks the hard grease lock as you turn. I’ve used throttle body/carby cleaner with a spray nozzle tube fitted to soften and CRC CO contact cleaner to flush. Then a spray grease using a syringe needle adapted to the spray tube to direct the flow, (or machine oil for non-grease oil type bearings like the old phosphor-bronze ones).
 
Just age and years of storage moisture caused the bubbling. Ran a previously recorded set of un-EQ’d clean and overdriven guitars through it to final test. I must say the filtering is very smooth without any of the artifacts you seem to get from plugins.
 
Thank you, Jakob.

Following up on this thread, I tried heating the shaft and turning with pliers, but the stubborn switch wouldn't budge. A little protected spritz of non-chlorinated brake cleaner did the trick. I then flowed in some oil and now all the switches are buttery smooth.

Spent the past couple days giving this guy a good scrub down and now it's ready for action.
Its nice when you find a simple solution to this sort of thing. I have rebuilt a few of this type of switch in the past it can be a challenge just fiddly rather than clever.
 
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It maybe:

Dirt and dust buildup: Over time, dust and debris can accumulate inside the switch mechanism, causing it to stick or become stiff.
Oxidation: Corrosion on the switch contacts can impede proper electrical connection and Precision Bearing movement.
Physical damage: In rare cases, the switch itself might be physically damaged, making repair needle roller bearings impractical.
 
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