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Apt Holman Preamp Switch Cleaning?

C

CVElectronic

Member
I recently decided to rotate the Apt Holman Preamp I inherited from my late brother back into service. I did some repairs on it for him years ago. What I found is that I'm having problems with the push-button switches, the Tape Monitor and Mute switches, causing intermittent signal interruption.

With some push-button switches, I know you can partially disassemble them (very carefully) for better cleaning. Can you do this for the ones in the Apt Holman Preamp, or do you just spray DeOxit into them?

I'd forgotten how good this preamp sounds.
 
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I don't know about disassembly but have found that Deoxit isn't always the best first step. On really tough problems plain old alcohol can sometimes solve the intermittent problems, then follow it up with the Deoxit to finish the job and provide a bit of lubrication. Don't power up after using alcohol until it's fully dry, as it can leave some condensation. Ideally, blow it out with some compressed or canned air.
 
Deoxit generally works as @ConradH says. These switches do cause the problems (particularly tape) and all can be replaced. Another approach is to gently use a 1/16" drill bit in a hand drill and make a small hole in the top of the switch, being careful to not let any plastic into the switch and then spray lots of deoxit. Generally is the switch is problematic I replace them
 
I was able to clear the switches by spraying with DeOxit and operating them at least 50 times, sometimes more. I checked all the contacts with my Fluke DMM on the low-Ohms setting. I kept operating them until I got a 0 Ohms reading on all the positions.

In terms of replacement, I wouldn't have thought that exact replacements of these push-button switches would still be available. (NOT the toggle switches)
 
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Alps Alpine, C&K and E-Switch are 3 "brands" that make this type switch. I have used the C&K before (although not in an Apt), they are good.

eg, a Mouser quick look shows these in-stock. Should work in the Apt, but there are others may be better suited. Look elsewhere too, Digikey, Arrow, etc.

https://www.mouser.com/ProductDetail/CK/F6U0A?qs=Pzq478CtQyeHO/NsJol5%2Bw==

https://www.mouser.com/ProductDetail/CK/FLT2UEETB?qs=cygERTaPE9CiYZEuMsUViQ==

OTOH, if you DO NOT USE the Tape loops, as a temporary (or permanent) fix, those switches can be bypassed with 2 short lengths of wire, eliminating the contact irregularities/faults.

Mute switch MIGHT be fixable with a wire jumper too, depends on how its misbehaving.
 
Zero residue contact cleaner first to flush it out. Then follow up with a cleaner that has some lubricant in it (Deoxit F5, or MG Chemicals Nu-Trol etc.)
 
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