View Single Post
Old 15th Mar 2019, 7:29 pm   #13
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,566
Default Re: U12 Rectifier - purple flash

Quote:
Originally Posted by Joe Ingle View Post
it worked well for a minute, then there was some crackling accompanied by the lamp dimming. I suspected one of the windings on the TX might be about to give out, so I shut down.

I then tried removing and replacing the rectifier in its socket, powered up again and it was fine. I ran the radio for about 4 hours this morning direct to mains with no funny noises or smells, so fingers crossed it's all OK.
This sort of suggests to me that there might be a problem with the valve holder...possibly one of the pins not making proper contact. have a careful look and see if any of them are broken or maybe just need clenching together (carefully).

I would have thought that if the transformer was breaking down, more likely the lamp would have brightened rather than dimmed. Of course windings can go open circuit which would probably cause dimming whereas shorted turns would cause the lamp to brighten. Shorted turns are unlikley to 'right' themselves but perhaps an O/C winding might correct itself particularly if the windings are terminated with solder tags and there was a dry joint at the terminal.

I would carefully check the valve holder first and then check connections at the transformer itself.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is offline