[gregb]

I have seen this many times on various old European made radios from the 50's mostly. These radios have their original tubes in them and are still working fine but flash when turned on from a cold start. Think about that for a minute, how many times has this radio been turned on since it was new? Thousands maybe tens of thousands and they still work just fine. I don't think it is anything to be worried about and it does seem to be something in how European tubes are made as I don't ever recall seeing this in an American made tube.

Gregb

[TV MAN]

That is a weird (to me) way to connect those filaments on that Fisher. It looks like they are using the filaments to bias the output tubes ... wow! I recapped a small signal tracer this week which uses a 12AX7, when I powered up to test, it flashed like you mentioned. It's a Mullard. Still don't think it is anything to be concerned about.