View Single Post
Old 8th May 2011, 3:43 pm   #1
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default Bush TV12 Poor Contrast

Hello, ever since I've owned my TV12B I've suffered poor contrast. I put it down to the tube; it already has ion burn and I just left it at that.

I'd already aligned the RF chassis when it was first restored using my AVO generator and Thandar digital RF frequency meter (for accuracy) so I'm confident that's not the problem.

But the other day I fired it up and realised that the brightness control actually makes the raster very bright indeed, (going to a white-out) leading me to think the tube cathode emission is ok. The rear contrast control has to be all the way up otherwise both sound and vision disappear (the control is not faulty and is the correct value).

I've done various swap-overs of valves in both main and rf decks using my one spare EF50 and changing valves between the signal and scan/audio just to see if that improves matters; it doesn't. Nothing suggested in the original service sheet improves matters either.

Can anyone think of anything to try? During original restoration a few years ago (involving recapping and cold checking all resistors) nothing in the RF deck seemed amiss; resistors etc were all spot-on. Might a crt fault still lead to poor performance despite the bright white-out i can get? I wouldn't normally say so but someone may know otherwise!!

Cheers
kevin
__________________
Kevin
McMurdo is offline