3-500 Taylor Graphite tube, need advise...

I've committed to a used 3-500 Taylor tube at a pretty good price. It was purchased a year ago and used very little. This will be going in an AL80b. The current tube is an emaic but it is gassy. It has a bright blue hue to it even after having it back in service after a very long lay off. The output seems ok. Would you pull this tube and replace it with this one? Or just leave it alone. With 2 tubes like this, should I cycle them every 6 months to keep them both active?

Is the new tube going to require any adjustments with the amp?

thanks

 

For tubes like the 3-500ZG, I'm not so wild about "used very little." I'd rather have a tube that was used quite a lot over the course of a year.

But it's probably fine.

If your current Eimac actually delivers full power without excessive grid current, e.g., 800W output with <150 mA Ig, then it's probably okay also.

Considering there's a lot of screws holding on the cover of the amp, cycling every six months might be more than needed; but many recommend cycling annually.

 

 I find it curious that Eimac says nothing about the need for cycling in "Care and Feeding of Power Grid Tubes".

 

What do you mean by "it has a bright blue hue to it"?

Is the glow in the vacuum space or on the inside of the glass?

Pictures?

73 de Jim, N2EY

 

 INDEED. Many of us were taken in by old wives' tales on Ham Radio. At one time I believed that the current in an antenna contributed to most of the radiation from it because that's what old timers were telling us. . . There's one born every minute.

 

Of course not. It's a Taylor tube!

 

The Eimac will probably be ok until it starts to arc. If it does arc that`s your warning to replace it before it takes a component with it. I understand wanting to keep spares,but I hate the idea of pulling a good tube just to cycle a spare. Every time you do that there`s always a chance of damage to the tube pins or socket.

 

That is a strange comment since broadcast engineers have been rotating tubes in order to reabsorb the gasses for many decades. Some tubes were notorious for outgassing (this is an internal process and is not to be confused with seal leakage resulting in reduced vacuum) and after about a year could not successfuly be restored. Since many of the 5KW and less glass tube BC stations have switched to SS I can understand why some are not aware of the practice......which works. Those big ceramic tubes with handles have their own set of procedures when required.

Ive kept the original 1986 Eimac pair of 3-500Z's in my LK-500 amp free of any visible gas by running hard about every 6 months as an AM linear and getting some good dark orange anode color. Before that it was run hard in weekend ARRL and CQ contests several times a year. Ive also restored many others (3-400Z, 4-250A/4-400A, 4-1000A, etc) using a publicized process long before the internet that can be used with any internal anode, thoriated tungsten filament tube, that Im aware of that has the gettering material on the anode. There is no such thing as a 100% success rate but Im well over 50% which includes quite a few decades dormant tubes. Some would not pass at 3000-3200V but worked fine in a SB-220 where regular use at color slowly improves them as reports of 10 or more years of performance from friends and customers have been normal. It also works with new Chinese tubes that have not been fully processed BUT NOT those that have not been vacuum pumped down enough. Chinese QC is a crapshoot.

Carl

 

I had a few 4-400's in storage for almost 20 years. Two years ago I pulled four of them out, plugged them in and they put out the same amount of power as they did when I put
them in storage. There was no blue colors inside of the tubes. They glowed bright red and worked great. I also had a 3-500Z Eimac tube in storage along with some 4-1000's.
They all worked as good as when I put them in storage.
No blue, no spitting and no sparking.
Barry

 

If what you say is true, why do 3-500Z tubes and many other types have getter material in the tube? If the getter material does not absorb residual air (gas) from the tube, why is it there? Maybe it's not there and it's a myth that 3-500z tubes have getter material in them. Explain. Thank You