I scored a bunch of tubes in a recent dollar sale - among the booty is a batch of Raytheon PCL84/15DQ8s made in Hungary. They have a halo getter on top (nothing unusual about that), but also a bunch of mirror-finish deposits on the pentode side that look like misplaced getter action, though there is no getter structure even close. The tubes alll look to be NOS, so this supposedly would have happened some time during manufacture. Insight?
"Migrating" getter material usually means that these VTs have been worked pretty hard. That was not unusual for a great many TV tubes, both large signal and small signal as well.. I've seen the same thing with 6V6s that were used in guitar amps.
They might have been cleaned up, but I highly doubt that they're NOS.
They might have been cleaned up, but I highly doubt that they're NOS.
Maybe I'll post a pic. These are all Raytheons in pretty much unworn but old boxes. The tubes are really clean and look unused. I have tubes (mostly sweep), that have had the snot hammered out of them so that the getter has migrated. These look different - and there's ten of them, looking like peas in a pod, not some lonesome ragtag. It almost looks like the getters were fired really hard while the envelope was still hot, so that some of the barium vapor squeezed down past the mica. Why the extra deposit ended up only on the pentode side of the tube is the mystery. I'll look closer, maybe there's a larger gap between mica and envelope on that side. The extra deposit I'm talking about is dense and shiny, not the brown stuff I've seen in abused tubes.
I can't imagine getter material coming thru the plate. Something is fishy with those tubes I think. If you have a magnifying glass and can peak thru a hole in the plate or around the edge, would be interesting to see whether the whole inside of the pentode is coated too. I would think that would turn it into a plasma arc tube shortly when the plate gets hot. Maybe you have the first positronic prototypes.
Don
Don
Hope that tube tester has a fuse in the B+.
I'm just getting my modded Tek 576 curve tracer going for tube tracing. (I will start a thread on that in a week or so.) Would be interesting to try one of those oddballs on it to see what's up (or down) there. Assuming they don't just fail outright.
Don
I'm just getting my modded Tek 576 curve tracer going for tube tracing. (I will start a thread on that in a week or so.) Would be interesting to try one of those oddballs on it to see what's up (or down) there. Assuming they don't just fail outright.
Don
These are probably made by Tungsram in Hungary. For some reason this sort of thing is quite common with some of their tubes (another example would be their EF80 pentodes), they are new and they seem just fine like that. I am not sure it's directly related to getter firing, but may have to do with the initial tube out-gassing or initial heater firing. Wether it's some product of the heater burn-in that radiates out from the insides onto the glass through the anode holes and looks like that, or subsequently somehow attracts the getter material, I have no idea.
Thanks for the replies. I'd never seen getter distribution like that before. The 15LQ8 is nice in that it has a high voltage rating for both halves, though the triode and pentode don't have specs as impressive as, say, a 6LQ8. I'm getting infatuated with some of the triode/pentode duals floating around out there, especially the ones where the pentode is designed for video amp duty.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.