UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - What happens if a valve's cathode becomes electrically detached ?

Chris55000 · 14th Sep 2021, 11:54 am

Hi!

I'm totally in agreement with your explanation as to what's happening inside your suspect valve – the only other thing to add is that it's almost certainly caused by a defective spot–weld between the cathode tube itself and the fine connecting strip/wire leading off down the glass "pinch" to the base pins – only thing you can do with it is what you've already done, return it to your supplier for replacement!

There has been mentioned on here in the past, and sometimes in servicing books and P.T. magazine, "welding" tricks on internal duffy connections to valve and C.R.T. electrodes using the very high flyback pulse voltages from valve–operated line output stages on vintage TVs, but it's an extremely dangerous technique to attempt only as a very last resort when all else fails, as quite apart from the personal risks, you can destroy a perfectly good and irreplaceable line output transformer attempting it!

Chris Williams

14th Sep 2021, 11:54 am	#2
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: What happens if a valve's cathode becomes electrically detached ? Hi! I'm totally in agreement with your explanation as to what's happening inside your suspect valve – the only other thing to add is that it's almost certainly caused by a defective spot–weld between the cathode tube itself and the fine connecting strip/wire leading off down the glass "pinch" to the base pins – only thing you can do with it is what you've already done, return it to your supplier for replacement! There has been mentioned on here in the past, and sometimes in servicing books and P.T. magazine, "welding" tricks on internal duffy connections to valve and C.R.T. electrodes using the very high flyback pulse voltages from valve–operated line output stages on vintage TVs, but it's an extremely dangerous technique to attempt only as a very last resort when all else fails, as quite apart from the personal risks, you can destroy a perfectly good and irreplaceable line output transformer attempting it! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!