3-400 tubes in the SB-220

Considering the SB-220 power supply, and other components, were designed for the old 1 kW input FCC regulations, I was wondering if anyone tried using a pair of 3-400 tubes to replace 3-500 finals? I've seen some good deals on the 3-400 tubes (they almost seem to be unwanted stepchildren) and I am wondering about picking up a pair for the future. I'd rather avoid relying on Chinese imports.

Pete

 

Unless they're making them in China now (I haven't heard that), I think 3-400Z's haven't been manufactured in at least 40 years. When Eimac started production of the 3-500Z, they discontinued the 3-400Z pretty quickly.

So, if the ones in question are "Eimac," I suspect they're at least 40 years old and if so are likely gassy.

 

I am not convinced that all vintage Eimac tubes have gone "gassy." Sometimes old wives tale are born of legend.

I have several 4-400 tubes that came from the WHYN 560 AM transmitter site back in the 1960s. I recently tried all of them in my SB-220
and they were fine. These were old back up spares that the chief engineer decided could be "retired," after years of service and subsequent
shelf time to meet the FCC spare tube requirements. Ditto for an early Eimac 1970s 3-500 that came with my amp when I bought it used. I had it stored for over thirty years, and it also went right to work with no pyrotechnics or other issues.

Pete

 

I'm not convinced they have, either. But they "may."

I have the original 4-1000 in my 6m amp that I built in 1984 (it's a feature construction article published in 73 and on line, and was the cover photo in a CQ magazine issue in 1985) and that was a "pull" manufactured in the late 1960s when I bought it! It still works fine and puts out the same power today it did 30 years ago, with the same drive power.

But I've had 3-500Zs "in storage" (still in original cartons) from the 1970s that weren't installed in anything until about 2000 or 2001. They all failed, immediately.

Maybe some luck involved, or different manufacturing processes used.

 

Most of Eimacs air ingress problems happened when they moved production to Salt Lake City and the seals were poor, most of these are in the 1986-89 time frame.

The other gas is outgassing from the anode and is common to all glass tubes as the getter material is coated on the anode and WILL release gas slowly with no use or never running the anodes with color to keep gettered.

I have 3-400Z and original Eimac/Heath graphite anode 3-500Z's (look like Amperex) that are as good as the day they were built but I do run them at color at least yearly.

There are a couple of 70's Eimacs including the ones without the base ring around here that are still fine. Unknowns are given a regettering on a 1000-1500V jig with positive bias to get some good color without enough voltage to sustain an arc before going into an amp and a RF test. Voltages are Variac controlled.

In the past I had a number of BC pulls 4-400A and 4-1000A that had outgassed from decades of storage and the jig brought most back to a useful life. There is no magic and no guarantee if a tube will rejuvenate, its strictly a crapshoot; sometimes there is just enough seal leakage to have to scrap it.

Carl

 

Hi Carl!

Interesting info on some of the older tubes. After being inactive for a couple of years I am back on the air and back building amps!

I had a look at my collection of spares and I have a couple of Eimac 3-500Z's still new in the boxes as well as a few Amperex 8163 also's new. I think I need to build a jig to "re-get" these tubes before trying to use them. Even the tubes in my amps that have not been run for 10 years could do with that.

What is your setup to do this? What voltages are you running? Would it make sense to do it in the amp but using a Variac to reduce voltages for the first few hours?

Thanks for the help and info!

73, Rudi de ZS6DX/V51VE

 

A change of diet can be helpful....even after 40 years old.....

 

Hello everyone,

this might sound a bit odd, but for some reason after seeing a photo of two 3-400 tubes glowing at 800 watts each... I find myself attracted to them like a moth on a early summer evening. They just look so darn cool! So, what amplifier do I need to find to purchase that has these amps so I can start enjoying that glow in my humble shack??

Thanks for you understanding of my new found addiction!

Dale
K7DNH

 

These can be found reasonably at times.

 

You may want to look for a Swan Mark I. I have a project unit I may want to sell. Have no tubes though.,