Daven / Langevin pots and attenuator - RCA BC-6A mixing console

[mikeydee77]

Hi there,

I wonder if someone on this forum will have seen these before...?

I have been asked to look at an RCA BC-6A mixing console. The main fault is with the power supply and that was easily remedied. Once up and running, the mixing controls of which some are potentiometer and some are attenuators are all very noisy. The RCA manual mentions cleaning them with "Davenoil" and I have also seen on www mentioned of using a typewriter eraser but no chemicals... (maybe just on the attenuators?)

My question is just a basic one on how to dismantle them? They are the black circular controls pictured below and appear to be sealed units.

Any ideas?

[Jon Snell]

They are sealed but acces can be gain if care is taken removing the solder from the tags and then easing the rear cover up and over the tags.
They are easily broken and not replaceable!

They may be wire wound.

[mikeydee77]

Thanks John... that is useful to know about the fragility. Usually something you learn via a bad experience.

Cheers.

[nevetslab]

As I recall, they are wire wound. I had obtained a number of them years ago, and, unlike the Daven or Cinema Engineering detented step attenuators, whose covers open right up for cleaning the large silver contacts in the thick wafers, opposite side containing the precision resistors, the Langevin pots did not come apart. In trying to open one of them, it DID break the cover. I cleaned up the remainder and sold them on ebay, and was sadly amused to see the price battle from buyers in Japan drive the price way up. I never did try to open a second one to find the secret in disassembly.

[mikeydee77]

I never did try to open a second one to find the secret in disassembly.

Thanks Nevetslab that has helped me come to a conclusion on this mattter. Cheers...

[Mick Bailey]

Are those metal cases with a rollover-edge retainer for the insulating disc?

[mikeydee77]

Are those metal cases with a rollover-edge retainer for the insulating disc?

Can't say about the insulating disc but looks like a rollover edge Mick. I think Jon Snell's reply above sounds correct that the case may be secured by virtue of the solder questions. I have not dug any deeper as yet as bit nervoud about causing damage. I am going to discuss that eith my client to see ift hey want to take a risk.

Having trouble trying to add more detailed pictures...

[mikeydee77]

Here are some more detailed pics esp for you Mick Bailey...

[Mick Bailey]

Ah, that's clear. The disc is assembled and then the edge rolled over afterwards, so there's a risk of cracking the disc as it will need to be flexed considerably and it's maybe made from SRBP. It's similar to quite a few capacitors and some automotive gauges. There's a special tool for unrolling the edge and re-rolling but the usual bodge way is to lever up the edge and pry it open with a screwdriver. What a mess. I've had success with this type of job using my lathe and a large wooden split collet to hold the body of the component and it can be carefully opened by turning the lathe by hand and using a custom ground tool.

Sometimes it's possible to drill a tiny hole in the body of an enclosed component (assuming no other access) to get just enough Deoxit in there to clean and lubricate contacts. You have to use a depth stop on the drill bit and ensure no particles end up in the body of the assembly, though and use the smallest drill you can. I have some syringes with fine needles and they only need a 0.8mm drill. Having some idea of the internal construction is helpful.