D&A Phantom 10 Tube One Tube Red Plating.

[EchoKilo]

Hello all, I have a 10 tube 24lq6 with a 6kv6a pre driver tube. The number 2 driver tube 24lq6 is red plating with just a few seconds dead key or talking. I've changed out the z14 plate choke, the 47ohm parasitic suppressor, 100 ohm cathode resistor, .01uf filment decoupling cap . Also tried swapping tubes ended up killing 2 know good tubes..Out of 10 final tunes only one is cherrying.. any help or direction is appreciated.

 

[nomadradio]

Um, does this fault appear only at one socket position?

If so, a bad socket or bad connection under it would sound likely.

73

 

[EchoKilo]

Yes, it's only one of the 24lq6 driver tubes. I was thinking about adding bias to the driver tubes like the 6 finals but I'm only seeing failure on one tube if it was all of them cherrying I understand that but just one I don't understand. I sprayed the sockets and checked continuity, but you made me wonder if there's any high resistance to ground. Also it goes worth mentioning the red plating only happens in high power, low and medium no red plating at all. I appreciate your time nomad I've learned alot reading your replies.

 

[EchoKilo]

Wow I feel like a dunce. I checked that socket out. So pin 2 and 6 are the grids obviously, some of the sockets has pin 6 removed others are left intact.. The one in question has both pin 2 and 6. So I removed everything off the pins completely isolated it and I found pin 2 intact but when I straightened it up to move it from ground there was nothing left and it broke off. My ah ha moment. Put in a known good tube and I didn't see anything noticeable in the way of red plating. I did however inadvertently put one of the tubes that red plated prior and it was not producing much I paniced for a moment. I guess they arent lying when the tube red plates it dont make long for the anode be stripped. Fingers crossed it stays that way its a nice preforming amp with a dose of nostalgia. I appreciate your input nomad.

 

[EchoKilo]

Now that it's gotten dark our I shut all the lights off and tested it one more time before I fully buttoned her up and its still very slightly turning red. Going to replace all the cathode resistors and parasitics in time and see if that helps. Still stumped it's only the one tube. I was convinced earlier.