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What Causes This?

ken99

ken99

Active Member
What causes these black marks inside these PL509 tubes? I have also seen them inside PL519 tubes. They only seem to show up on the used tubes.

I realize that some of the black spots are the getter flash. I am talking about the "stains" that appear inside the glass.

See attached photo.

ken99
 

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Nothing to worry about. I have Mullard EL84's with those same type of stains and mine still play fine and show excellent emission on my tube tester.

I think I heard or read somewhere that this is normal and that it was actually part of the manufacturing process.
 
My 6BQ5s look like that also,,, don't know what make they are, tho... What are PL509s, never heard of them...
 
Sounds logical

These stains do seem to be concentrated around the micas. Seems logical. Interesting.

The PL509:

http://www.r-type.org/exhib/aaa0021.htm

http://www.radiomuseum.org/tubes/tube_pl509.html

I have a McAlister amp that runs four of these babies.

I don't have any with the stains on them. I have a set of Japanese Mullards with about 1000 hours on them, and not one stain. I also have lots of other brands, but almost all of them are NOS.

Thanks for the info guys.

ken99
 
Much like a white flash at start up, that black stuff is a VERY good sign. I always called them smoky Mullards.:music:
 
thanks

I was just curious about these stain marks. I don't have any tubes with the stains in them. My amp works like a top - no need of checking or repairing anything. I have seen tubes with these stains for sale before and often wondered what the heck caused the stains. I have never ever purchased them because they make the tubes look dead ugly.

thanks
ken99
 
valve dude said:
over bias to much EHT bad PSU
one of the plates is burnt i would be checking output tranny it more then likely faulty
Click to expand...

Hmm, been an electronics tech for over 40 years and have never heard or seen this type of fault causing the tubes to look drippy smokey!
 
:thmbsp: I think so also, I have had some tubes that were well used, and the dark spots lined up with holes in the plate, so I believed that it was burned away material from the cathode or plate
Pio1980 said:
I think it's electron stream tattooing of the inner glass surface.

Sent from my SM-N900V using Tapatalk
Click to expand...
 
Heat stress on plates leaves discoloration near vent holes and is indication of red plating and is bad. However, early Mullard el84 RX2 came from factory with dark stains on inner glass and they are very desirable and not an indication of wear. Dark spots in the getter flashing is also normal on 6922/7308 and F2A tubes
 
yes the is right but what i saw in the photo in this thread was a valve with an orange red spot witch is coursed from the bias being way to hot EG the bias currant has A not been readjusted once a new pair of electron tubes were fitted B the EHT supply has gone wonky C the cathode resistor has lost its value and or has been toasted and none of the metal parts inside any valve should not have any discolouration some NOS will have pencil writing on the outer metal the black getter bloop stain yes will be on the class
 
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