I’m a newbie when it comes to ceramic tubes. The 4cx300 variety is what I’m trying to use. I was fortunate to get several used 4cx300y tubes from a generous Ham out West for little more than shipping (callsign added later when I dig it out) and I purchased some NOS tubes from eBay: Some sealed in cans and some in unsealed boxes.
For this Post, I tried two eBay tubes (different Sellers) sold as NOS 4cx300a. They came in the boxes with the 1-piece, yellow plastic insert. One 4cx300a had no marks whatsoever and looked pristine. The other had light marking on the tube pin/tabs but otherwise showed no sign of heating or anode clips, etc. Almost pristine.
The two used 300y tubes were well-worn with obvious signs of heating, pin/tab and anode clamp scratches, heavily tarnished, hard to read the text, etc. I used the worst pair of 300y tubes for first Power-up attempts. After I had about 130W from an old CB and addressed several issues that arose, I thought it was time to try the NOS 300a tubes. I switched the Bias, Screen and Plate voltages and began the conditioning process I read about online.
I found articles advising to run only the filaments w/ blower on low for at least 12 hours when installing new tubes that were stored for long periods. It’s a new build and requires babysitting as this would be the first long stretch of Power On. I managed about 6 hours uninterrupted and a few more hour-long periods with just the filaments On, tube blower running low. Admittedly, a lot less than 12 hours/overnight. This process required more than a week as cooling issues required revising the 40mm fans moving air underneath the chassis.
Long story short, the NOS tubes made zero output. Like dead, wtf? I put the old 300y’s back in and they still produce. Stop, backup... re-verify the different settings for the 2 tube types and do it all over again. Same damn result. Another filament conditioning only stretch? Granted, 5-6 hours is far from overnight but completely dead? Time to take out my can opener? IDK Have one of each and need 1 more can but buying NOS is beginning to feel like buying a lottery ticket.
neil, n2eye
NYC
For this Post, I tried two eBay tubes (different Sellers) sold as NOS 4cx300a. They came in the boxes with the 1-piece, yellow plastic insert. One 4cx300a had no marks whatsoever and looked pristine. The other had light marking on the tube pin/tabs but otherwise showed no sign of heating or anode clips, etc. Almost pristine.
The two used 300y tubes were well-worn with obvious signs of heating, pin/tab and anode clamp scratches, heavily tarnished, hard to read the text, etc. I used the worst pair of 300y tubes for first Power-up attempts. After I had about 130W from an old CB and addressed several issues that arose, I thought it was time to try the NOS 300a tubes. I switched the Bias, Screen and Plate voltages and began the conditioning process I read about online.
I found articles advising to run only the filaments w/ blower on low for at least 12 hours when installing new tubes that were stored for long periods. It’s a new build and requires babysitting as this would be the first long stretch of Power On. I managed about 6 hours uninterrupted and a few more hour-long periods with just the filaments On, tube blower running low. Admittedly, a lot less than 12 hours/overnight. This process required more than a week as cooling issues required revising the 40mm fans moving air underneath the chassis.
Long story short, the NOS tubes made zero output. Like dead, wtf? I put the old 300y’s back in and they still produce. Stop, backup... re-verify the different settings for the 2 tube types and do it all over again. Same damn result. Another filament conditioning only stretch? Granted, 5-6 hours is far from overnight but completely dead? Time to take out my can opener? IDK Have one of each and need 1 more can but buying NOS is beginning to feel like buying a lottery ticket.
neil, n2eye
NYC