Discussion in 'Amateur Radio Amplifiers' started by KB4MNG, Mar 11, 2013.
The way a lot of hams talk, it's not obvious at all.
73 de Jim, N2EY
A lot has changed Steve. We're older, boatanchors are worth money, rectifier diodes don't need parallel capacitors for the last 30 years.... One thing at a time.
Metal base means zero to the supposed internal gassing due to prolonged storage. The base is outside the vacuum. Compare apples to apples. Eimac only. There are 4-400s whose plate structure looks exactly like a 3-500. Many don't. They look like 4-250s with fins added. Still the 4-400s with the cookie cutter plate structure (similar if not identical to the second generation 160 mu 3-500) are not known to fail from being shelved.
There are still plenty of AM broadcast engineers around who would know. I'm just a guy with a lot of old stuff in my basement.
Anyone with battle experience? Is the "gear" plate 4-400 problematic verses the finned plate style?
Maybe the 4-400s with the gear like plates WERE problematic. I auditioned a pile of these tubes last winter for use in a Viking 500 here. The finned ones are still here. 1 "gear" plate 4-400 filled with smoke when lit. Another had very poor emission. Off resonance plate current was way down from the others tested.
Seems to me there's a whole lot of Chicken Little advise on ham radio sites. Discourages new ops from anything but buying new stuff. Then the same guys complain new guys know nothing.
One must break a few eggs to make an omelet.
True, but I mentioned it because it's an obvious difference. The metal shell is normally plugged into a socket having grounding clips that ground it and add mechanical support to the base (at least, in all the commercial transmitters I've ever seen using the tetrodes) and make it very difficult to install the tube at a "tilt," which places stress on the pins -- the 500Z doesn't have that feature.
I mention the difference in anode material mostly because it seems likely the gettering process would be somewhat different, based on the metal used (not the gettering material, but the base metal), and that could make a difference as well.
An interesting observation: I've used 4-400As in 3-500Z amplifiers lots of times, even in SB-220s. An SB-220 run at 800mA Ip for a while can make the filament pins so hot they can melt solder, and I've had that happen. But the same amp run the same way with 4-400As in it...I've never, ever seen that happen. This may reveal a difference in the way the pins are attached.
Put some well bypassed screen voltage and a little negative bias on that 4-400. Drive it through the cathode now with same drive used in the 3-500Z test : )
It would be intructive to have a list of all the 3-500Z variations and production dates.
Maybe the problem ones from Eimac were produced near the time of the problematic 8877s.
Unless Collins never had a definate platform for the 30L1 before it considered using a 3-400 (which you say Eimac designed special for that amp) you could not fit a pair of them in a 30L1 with an atomic bomb.
RCA didn't exactly stop making transmitting tubes.
With the acquisition by GE in the 1980s, a management buyout of the transmitting/microwave tube division occurred to form Burle Industries, at the same facility/location (Lancaster, PA) as the RCA transmitting tube plant. They still make tetrodes, magnetrons and some other stuff there, but I don't think they make any glass transmitting tubes.
I'm not ready to give up and go solid state even if you are right. It's plain boring.
All the more reason for not rotating tubes.
I wouldn't expect they would release that info either. The information could be generated by owners of tubes. Look at the date code, match it to a picture, post info somewhere. There are certainly a lot of people on amateur radio websites discussing this bottle.
There was a PDM AM broadcast box which used a 3-500Z. I know one guy had one on 160. He would have some info on tube life.