[Joe Ingle]

One of my favourite sets - a GEC BC3754 which I've been using every couple of weeks for about five years now - blew its 1A fuse today when I switched it on.

I powered it up with a lamp limiter and the rectifier (U12) was glowing bright purple, and the lamp limiter was bright.

With the rectifier out, the lamp limiter was dim and the rest of the valves lit up as normal. I checked the voltage at the rectifier base and they looked good - about 600 volts and 4 volts.

I've never seen anything like this before, but I've read elsewhere on the forum that purple can mean air has got into the valve, so would it be safe to assume that it's dead?

If this is the case then does anyone know any useful and more available equivalents - a quick trawl on the usual sites suggests U12s are rare and a bit pricey. The Valve Museum has the following suggestions:

43IU
DW4/350
R2
R3
R4
RV120/500
U14
UU5

In the worst case I could always use a couple of diodes, but I'd like to keep the radio original.

Thanks all,

Joe