Discussion in 'Amateur Radio Amplifiers' started by KB4MNG, Mar 11, 2013.
Only takes 100mA to kill you.
Before WW2, tantalum was a popular material for power tube anodes. At some point during or after the war, many tubes converted to a zirconium coating. This is often one of the differences between a power tube and its A version - for example, the 833 and 833A. There may be other differences.
Not sure about molybdenum.
73 de Jim, N2EY
You usually don't have to worry about H2 gas that much since there is so little of it in the atmosphere.
The other inert gasses are in much larger quantities with a couple of exceptions. Xeon being one of them.
H2's primary use in industry is for leak testing of hermetically components. H2 does pass through glass and as a matter of fact H2 in a capillary tube is used as a calibration standard for H2 leak detectors they come in a mount and have their leak rate stamped on the mount. H2 is problematic around vacuum systems and can be difficult to purge out of a system that relies on an LN2 cold trap and an oil diffusion pump. There is no better trace gas than H2 which means in order to accept the good you must deal with the bad.
That is the extent of my experience with high vacuum systems (10-8 tor.) it was kind of fun even though a fanatical sense of cleanliness is mandatory, and patients while everything takes its sweet time pumping down.
For those who don't know the units of pressure.....
Sea level is 760,000 tor.
Sue, the popular tubes use zirconium which will combine and then release the gas many times; tubes are ready for replacement and regettering still functions.
As far as the BC industry I guess Bozo doesnt know that driver stages for RF and audio use the popular 250-500W triodes, tetrodes and pentodes. Those same tubes are/were used in output stages also, and many of the day-night stations have a low power switch and are run 24/7. Apparently his version of the BCB industry is as bad as some of his other rantings.
The tantalum anode was introduced by Heintz and Kaufman which prompted Eimac to either buy them or the rights around 1934 (I forget the details but Eitel and McCullough both worked their first) and then they really took off. My avatar is a pair of 304TL's that arent even running hard. The HK-354's in one of my AM amps run almost white in normal operation but in deference to their age I cranked them down a tap on the transformer. H&K also supposedly developed the glass that could handle this along with the RF.
Lou, you know regettering is possible so why dance around it? Several have reported success on the other forums you visit
What is the difference inside the glass envelope of an Eimac 4-400 and a 3-500Z besides the element spacings and screen grid?
Thanks good information.
I havent been inside one but in GG service it takes about 25-30W more drive for a pair for the same output as a 3-500Z's using a SB-220 as the test bed. Its a cheap replacement in a pinch except several amps will require the 3 grid pins of the socket to be directly grounded. The PL-175 has higher gain and is about a perfect swap. Purists may want to tweak the bias.
Been there more than a few times. I'm asking because 4-400s are not fabled to need rotation into service every 6 months while 3-500s must be used or they supposedly turn to dust. They look very similar in construction to me.
Still watching many satisfied buyers of pre-owned 3-500Zs on epay.
Down to my last pair of 3-400s which were wrapped in newspaper with Watergate headlines. I'll blame Nixon if they don't function.
Hmmm...they don't, to me.
Their pinouts and filament requirements, and even anode ratings, look similar or identical. But the 4-400A etc. have metal shells at their bases and different anode material (metal vs. graphite) and quite different internal construction -- although 3-500Z's have varied in construction quite a bit over the decades and most new ones don't look like the original Eimac product internally.
Unfortunately, the manufacturers seem to keep the metallurgy and processes pretty closely guarded, so I can't find if there are differences in the Kovar pin seals and such; there might be, but it's hard to tell. I "think" they're all gettered with Zirconium powder applied to the anodes, but even that process is likely different depending upon the base metal of the anode, and all the "new generation" 500Zs are graphite (the original 1960s-1970s Eimacs weren't).
I have a HB 4-1000A amp I built in 1984 using a "pull" tube that was date coded in the 70s, and it's transmitted thousands of hours for me with no signs of deterioration at all (running about 1500W PEP output, which is a bit below its ratings). Some original Eimac 500Zs seem to have enjoyed similar lives; I don't know of "any" modern 3-500ZGs, which is really all that's available today, which have. Something's changed.
You're missing the point completely. It is this:
In commercial service, transmitters are built and operated to very different standards than in amateur service. Everything in commercial service is run more conservatively, and frequency changes are much less common than in amateur service. And most commercial service puts many more hours on a transmitter per year than a typical amateur will put on an amplifier in ten or twenty years.
Commercial operation also tends to involve preventive maintenance, while hams will tend to use something until it fails.
73 de Jim, N2EY