8mm Forum: failed tube amp in Bell &Howell 8399

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Topic: failed tube amp in Bell &Howell 8399

Robert C. Kline
Junior
Posts: 2
From: Austin, TX
Registered: Dec 2005

posted February 22, 2006 01:08 PM

The tube amp in my 8399 was functioning perfectly well until I started a third, 20 minute film, at which point the speaker output had dropped to a level that was barely audible, even at full volume. So far as I can tell, all components in the amp are original; so I suspect that after 40+ years the culprits could be soft tubes and/or a failure of one or more of the unit's capacitors. I would appreciate any ideas out there as to how to repair this problem or a referral of someone to whom I can ship the unit for repair. Paul Ivester has suggested Ken Layton, but I don't know how to contact him.

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Bob Kline
Austin, TX
512.658.1453

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Kevin Faulkner
Film God

Posts: 4071
From: Essex UK
Registered: Jun 2003

posted February 23, 2006 01:24 AM

The tubes tend to go slowly so I dont think it's that. It's more likely to be a dried up capacitor. Make sure you have got some muck on the sound lens etc.

Kev.

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GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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John Whittle
Jedi Master Film Handler

Posts: 791
From: Northridge, CA USA
Registered: Jun 2003

posted February 24, 2006 09:13 AM

This is a classic example of a coupling cap failure. This happened so often with the old RCA 400 that the schematic I got from a service man had the part circled!

If the "noise" from the amp is the same, it's likely in the early stages such as the sound input to the first stage.

BTW I thought that the 8399's had the solid state amp, could it be you have a 399?

John

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