Which is best 3-500Z tube and why?
I need a replacement tube for my AL-80B amplifier. Eimac tubes dont seem to be available any longer unless I try to get NOS on ebay. Looking at rfparts.com there are several options. Amperex are listed at $319 + shipping and RF parts lists their china made brand around $180 and taylor's (also china made) for a little less. Which of these options are the better choice and what are the pros and cons of each? As for the NOS Eimac tubes on ebay, is it a concern that they are old date codes or if they are Z or ZG versions of the 3-500? Is there a better source than rf parts to order tubes?
Go RF PArts
I have had a little experience with the RF parts tubes, first in a Kenwood TL-922 and then in an Ameritron AL-82.
In the '922 I had to go through three separate sets of the RF Parts tubes to finally end up with one good set in the amp. This was over a three-four year period.
Then, taking a gamble, I got the AL-82. I had a tube failure almost immediately as the solder in the filament pin melted out.
In spite of that, Ameritron immediately replaced the Taylor 3-500ZG and so far, so good. Rf Parts is also very good in the warranty department. It is just too bad that the manufacturer in China seems to have QA problems.
My opinion is that even with the QA problems with the Chinese tubes, we're still better off to buy new with a warranty than to buy NOS and be stuck with a possible problem. The 3-500's are notorious for having pin seals go bad after extended storage.
RF parts is still good in my book because they will give you a two year warranty on the tube and replace it with no hassle if it goes bad.
My opinion only of course...
I replaced the 23 year old Eimac 3-500Z for an 3-500ZG from RF parts.
That in the Heathkit SB-1000, the Eimac tube went soft and the new RF parts tube does what the carton said.
Little bit more gain, running well, good output power, but always used with less drive after the tune up to 500 or 600 watts.
RF parts looks like a good trade, if i'm in need of more, i'll directly order there again.
Licensed since 1977
Gary, is this an opinion or fact? Not trying to be smart about this but have read it before. I cannot understand for any tube with glass around a metal wire will potential problems along this line. I use tube gear almost exclusively and have never seen this problem even with tubes manufactured in the early 1930s.
Originally Posted by WG7X
Is this problem specific to the 3-500s or is it across the entire spectrum of tubes manufactured in China? So if you would please give me reference or help in any manner, I would appreciate it.
::3-500Zs have been notorious for short shelf (storage) life since Eimac first started making them. Almost everybody who's designed and manufactured amplifiers and used thousands of these tubes recommends: Don't keep spares on hand unless you rotate them through a working amplifier, and get them "very hot" (anodes red/orange) about every six months. Otherwise spares often go bad on the shelf, becoming gassy beyond the possibility of repair by the gettering process, which only occurs when the anode gets very hot (filaments won't help).
Originally Posted by W5JO
It's a function of the gettering process for these tubes, which evidently is deposited zirconium on the graphite. This is a problem unique to this tube design and construction materials. "Smaller" tubes like receiving tubes and 6146s, and ceramic-metal tubes like 4CX250s and such are in a different category and can have extremely long shelf lives.
My 75A4 manufactured in 1956 has all its original tubes, which are now 53 years old. I know they're original because I've owned the receiver since 1970 and am the second owner, and I've never changed any of them, and every tube in the receiver (made by RCA) still has the "Collins" logo on it. I use it pretty often, I'd say at least once a week.
The Transatlantic Cable laid by AT&T when I was born uses hundreds of tubes and they all still work.
Steve I understand that the story is "everyone recommends" the tubes not be kept for the reason you mention; however I would like to see some documentation of that statement.
As I said in my original post, I have never seen it and have searched for the recommendation to no avail. So when I saw this quote I just wanted to know if it is a myth or actually documented anywhere. Can you help with a direction to documentation?
::I learned this for myself when I had a brand new pair of Eimac 3-500Zs from 1982 sitting in my closet as "spares." I tested them upon purchase from Eimac in an SB-220 and they produced 1100W output, so all was well. I carefully packed them back in their original Eimac cartons and set them aside.
Originally Posted by W5JO
I plugged them in in 1988, and the filaments looked fine. I applied high voltage and the and the amp immediately blew the primary breaker. I removed the tubes and the breaker held. Installing the tubes again blew the breaker again. I suspected something had gone wrong with the tubes while they were "just sitting," so I sent them both off to Eimac SLC to see if they could determine the problem.
The letter I received back indicated both tubes were gassy beyond repair and arched at less than 3000V. They were not under warranty, and Eimac did not repair glass tubes; however after a phone call with Reid Brandon there, it was agreed they'd replace the tubes with new ones, anyway (nice of them).
The new tubes worked fine. Subsequent conversations indicated these tubes are not recommended for prolonged storage periods, although I've never seen an Ap Note or anything on this subject, from Eimac or anyone else.
I was satisfied, as the vendor 'fessed up and replaced the out-of-warranty tubes; probably because I still had the original packing, and the paint on the tubes was still dark red, an indication they'd never been hot. (The Eimac paint is temperature sensitive and changes color when the tubes have been really used.)
The experience made a believer out of me.
Since then, I've seen many threads by very knowledgeable people who know more about the interior contruction of transmitting tubes than I, tell pretty much the same story: These tubes can have very long "operating life," as long as you get them hot pretty often (turn the anodes red by applied power), but not so much if you don't. That seemed to be the case in my situation, so I believe it.
I'm with you. I've not seen this so called problem with dozens of this tube type over many years. Must be my luck.
Originally Posted by W5JO
Look to the future. You will see the same idea put forth in a month or two. That will make it into fact.
Same for a half dozen other subjects here.
Thanks for the input
Thanks for the input on the tubes! I've been wondering about the shelf life issues I've heard with the eimacs and was thinking it might be a problem to get the NOS from ebay. Regardless if it is a well founded rumor or a documented fact, I think I'll stay away from the NOS tube. I know some have had good luck with them but my luck is never that way and murphy always finds me.
Between the RFP brand tube and the Taylor, which is the better choice?
That scenario was exactly my original problem with my Kenwood amp. After an extended storage period, one of the original Eimac's went south and caused a few issues.
Originally Posted by WA8KJP
I don't have that tube, but I still have two of the others that went. Analysis at RF parts indicated that all three of the problem tubes, two grid shorts and one anode short were caused by gas in the tube allowing a flash-over/ arc to occur thereby destroying the tube.
The first time that happened with the original tube(s), it also took out the grid bypass choke and a few other components. After modification, the subsequent failures only affected the tube itself.
But after all that, I still have a bit of faith in the RFP tubes because they stood by the warranty in all three cases, and then Ameritron also warrantied the tube in my current amp.
RF parts sells these tubes to most of the amp builders that still use 3-500 technology. That was one of the reasons that I bought another 3-500 amp. If the overall quality is good enough for Ameritron, Ten Tec, and other manufacturers, its good enough for me.
I think that you will be OK to buy either tube from RF parts.