Jim, it could be ?reflection. The OP didn’t give much information like if the amp works, reads hi voltage, gives idle current if keyed up, etc etc. ?I?agree with you but I’m just trying to get the OP to do something to obtain more data. ?Yup you are correct I have hi pot brand new Chinese tubes right out the box and some will conduct at just over 400volrs. ?I like to see around 1500. ?I’ve test some old ?Eimacs G-F to almost the P-G amount. ?Rare but I have seen it. ?Chinese are mostly ok P-G upwards of 7kv. ?If you didn’t accept just above 500v G-F you’ll be rejecting lots of tubes!
On Thursday, November 30, 2023, 7:08 AM, Jim VE7RF <jim.thom@...> wrote:
Lou, on the 2nd pix, it looks like BOTH tubes are going red.? My guess is.... it's a grid to cathode short on one or both tubes.?
The baffling part is..... his grid and plate current meters are still reading zero.?
More baffling is..... it takes 5 mins for the problem to manifest itself.?
Typ with a grid to cathode short on just one tube.....? BOTH tubes will go red asap, as soon as you turn on the amp.
?
On a related note, on Eimac 3-500Z's, they typ hi-pot test 5 kv? from grid to cathode ( good tube).? ?On all the chinese ( good tube)? 3-500Z's.... they all only hi-pot test 1 kv from grid to cathode.?
