The AM Forum

Ameritron in an email said they did not use the Amperex 3-500z, since 2001 because of filament issues?  I have 4 of these tubes that I bought in the 90's and they are fine. I have thought that Amperex was of very good quality? RF parts is selling the Amperex 3-500Z for $320!!!

Anyone have anything technical to say about Amperex?

Thanks,

SS

I read somewhere carbon plate 3-500Zs were tuffer on the grid structures because they hold heat longer. So keep they fed with plenty of air.

What does this have to do with the "Filament Issue" as described in my question?

Thanks,

Stan S.

The failure mode was sagging elements resulting in a Grid to heater short.

The grid to fil spacing of a 3-500 is only .004 inch ... about the thickness of a common sheet of paper ... not my favorite tube ...73 ... John

I find the Amperex tubes, made by Covimag in France, are fine in my 314R1. They are rugged. I suspect they are more costly than Far East tubes, and Ameritron or whoever has to justify their decision, so they said something about filaments. Haven't heard anything, but i suppose that Covimag could have had a problem for a time. But usually these things go away, once an engineer does his job at the factory, with enough customer complaints.

Thanks, finally a report that has real logic.  Thanks,  SS

John, do you have a timeline on where Amperex built their TX tubes? Going back to Hicksville if possible.

Ive also never had a problem with their 3-500's of any date code and actually try to search them out.

In a SB-220, going to the higher speed fan sold by Harbach keeps them nice and contented.

Carl
KM1H

I sure don't have that info. They have been made by Covimag for quite some time, and it is an old Phillips plant.

By the way, I checked yesterday, and noted that at work we switched to using Amperex 3-400Z (yes, they still make these) about a year ago, and have probably used half a dozen with no ill effects. We used to have Eimacs, of course. Never tried Chinese copies. I didn't want to redesign the systems to use 3-500Z unless I was forced to, as the chimney height, the slight change in mu, etc might require some engineering. They are used as a pulse amplifier, inverting. When the tube is conducting, the pulse is off. When they are cutoff, the following stage makes a pulse. The pulse is about 1 mS long, 60 times a second, driving a 4CX3000A cathode follower which then supplies a pair of 4CW250,000B tetrodes their screen voltage (~2 kV pulses).

I was overjoyed to find that Covimag still produce the 3-400Z so that we could continue using this 40 year old designed system (in 5 places) at the particle factory.

Happy New Year to all.
John
K5PRO
in white New Mexico

Those 3-400s are nice. I have a few here. Too bad they didn't keep the mu the same in the 3-500.

Interesting that I have a pair of Amperex 3-400Z's and a pair of Sylvania's 3-400Z's for the RCA SB-1K. I have often heard the Amperex's are fairly hearty.

Was it something to do with the solder melting in the pins that made the filaments intermittent?? Lack of air flow?? OR am I thinking about another RF Tube???
Fred

I had a Heathkit SB1000 and there were issues with the microwave oven POS colling fan that may cause problems with 3-500SZ's

Fred