8mm Forum: B&H model Filmsound 8636 valves

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Topic: B&H model Filmsound 8636 valves

Peter Eastland
Junior
Posts: 2
From: Milton Keynes, Buckinghamshire, UK
Registered: Sep 2008

posted October 02, 2008 05:46 PM

Hello My father (84) has a B&H model Filmsound 8636 which he uses. it is an AC/DC version.
Does anyone have any information on the valves (tubes) used for the amp please. It has 4 valves 9 pin type.
one is marked UCL82, and another UCL8? so probably both are UCL82. However the other 2 are not marked except one says Hi Fi. The HiFi marking does not appear to have any meaning.
If anyone can help identify the unknown valves it would be appreciated. Dad does not do e mail or internet etc.
Many thanks Peter

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John Whittle
Jedi Master Film Handler

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

posted October 02, 2008 09:31 PM

Peter,

While I can't help you with identifcation (we use an entirely different system like 6GT36 where the first digit is usually the voltage of the filament and GT would be a glass tube or an output tube might be a 50HT24 or a preamp 12AX7).

Don't be too quick to think the problem is with the tubes (valves). A classic B&H optical sound projector has a phototube to pick up the sound which is usally shielded, then there is a pair of tubes that provide a high frequency AC for the exciter lamp, a DC rectifier tube, preamp and output tube. The classic amps I've seen have this compliment. If you have fewer, then you may have a hybrid amp which is part transistor and part tube.

BUT, usually the problem is with old electrolic capacitors. Projectors in the home really don't get thousands of hours on the tubes, but they get years of age on the old capacitors which dry out and fail in the circuit.

Most tube amp rebuilds I've done are strickly replacing the passive components (resistors and capacitors). Old high value resistors have a tendancy to go up in value to infinity (open) and old capactors drop to zero (open).

I trust someone will be able to supply you with information on the schematic for this machine.

John

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Maurice Leakey
Film God

Posts: 5895
From: Bristol. United Kingdom
Registered: Oct 2007

posted October 03, 2008 04:41 AM

Peter

My 8636 uses four valves which are all the same type. These are 50BM8, an alternative for these is the UCL85.

The amplifier also uses transistors.

As the model is AC/DC be very careful when inserting the speaker plug. Only do this when nothing is connected to the mains, the reverse is also applicable. This is because the plug tip momentarily shorts across the contacts. If you do this it will blow a fuse.

The amp gives superb sound, but the mains lamps leave a lot to be desired!

--------------------
Maurice

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