1569a

[Doc B]

Hello Everyone,
I am hearing some pops when powering up one of my 1569As. I have retensioned and cleaned all of the sockets. I noticed that the bias potentiometer feels rough and I hear the pops when biasing the amp. Does this sound like the culprit? If so, where would be a good place to by a replacement? Any help would be greatly appreciated.

Doc B

[Todd W. White]

Oooh - that's a Clarostat pot, if I remember right: very hard to find them.

You might try Antique Radio Supply...

[rafaro]

Some of these pots can be opened and cleaned using tuner cleaner available from RATshack for $$. Give it a try.

[Richard C.]

Doc B,

Do you mean you get the noise pops when you are changing the bias setting? How about if you tap the control?

Anyway, most carbon controls (except military grade), can be spray cleaned/lubed right thru the hole above the terminals. You do need to use a cleaner that will leave lube on the carbon surface. Bare, clean carbon will not last, and will actually be damaged beyond easy repair. Wirewound controls can be left dry.

Richard C.

[Doc B]

Hi Guys,
I tried to clean it but it did not work. The bias pot on the other amp turns smoothly and holds the bias. The bad pot is loose when turning, makes a scratchy sound when biasing, and does not hold the bias well. I think it is time for a new pot. Any recommendations would be greatly appreciated.

[Richard C.]

Doc B,

You will find a very nice replacement "Bournes" control in "Mouser.com". You need a 5 K ohm linear carbon, conductive plastic, etc. potentiometer. Page 474 has a 2 watt screwdriver adjust, "3852A-162-502A". If you need a longer shaft, you can search around these pages for the closest one.

Richard C.