ECL82 triode grid emissions? - UK Vintage Radio Repair and Restoration Discussion Forum

PJL · 15th May 2007, 12:12 pm

I have a problem with an ECL82. On my tester it is showing no leakage but is passing some current to the anode. Am I right in thinking this a grid emissions problem as opposed to gas which would conduct to the cathode?

Mike Phelan · 15th May 2007, 3:52 pm

PJL
If it is, and I am assuming it is used as an output bottle, with no signal present (disconnect coupling cap) the anode voltage should not change if you short the grid to chassis.
It sounds as if you may have already done that; is it possible there is a leak elsewhere - valve base?

PJL · 15th May 2007, 8:09 pm

Hi Mike, in the set the valve causes motor-boating not helped by the very high 10M grid resistor used for biasing. It was more a case of trying to understand why the spot on my Mullard tester went up rather than down when testing for grid current.

I guess I need to dig out 'The Book' but I assume gas causes the grid to conduct to the cathode but grid emissions would result in current flow to the anode. It passes leakage tests.

PJL · 16th May 2007, 10:43 am

I read Langford-Smith. Grid emissions and gas increase the negative grid current. The CG voltage is zero in the mullard tester so some positive grid current would be expected so it looks like the motor-boating is probably not the valve although strangely a replacement fixed the problem...end of thread

15th May 2007, 12:12 pm	#1
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	ECL82 triode grid emissions? I have a problem with an ECL82. On my tester it is showing no leakage but is passing some current to the anode. Am I right in thinking this a grid emissions problem as opposed to gas which would conduct to the cathode?

15th May 2007, 3:52 pm	#2
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: ECL82 triode grid emissions? PJL If it is, and I am assuming it is used as an output bottle, with no signal present (disconnect coupling cap) the anode voltage should not change if you short the grid to chassis. It sounds as if you may have already done that; is it possible there is a leak elsewhere - valve base? __________________ Mike.

15th May 2007, 8:09 pm	#3
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: ECL82 triode grid emissions? Hi Mike, in the set the valve causes motor-boating not helped by the very high 10M grid resistor used for biasing. It was more a case of trying to understand why the spot on my Mullard tester went up rather than down when testing for grid current. I guess I need to dig out 'The Book' but I assume gas causes the grid to conduct to the cathode but grid emissions would result in current flow to the anode. It passes leakage tests.

16th May 2007, 10:43 am	#4
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: ECL82 triode grid emissions? I read Langford-Smith. Grid emissions and gas increase the negative grid current. The CG voltage is zero in the mullard tester so some positive grid current would be expected so it looks like the motor-boating is probably not the valve although strangely a replacement fixed the problem...end of thread