416B dangerous tube?

[serengetiplains]

Hi! I'm thinking I might want to purchase and play around with the Western Electric 416B planar triode. I've read a few posts about this tube, a few of which suggested it uses the possibly dangerous substance beryllium oxide in its construction? Can anyone comment or expand on this? My family line already has enough genetic mutations it's working through ..... don't need more.

Thanks!

[Peter M.]

As far as i know, beryllium and beryllium oxide is perfecty safe to use as long as it is in solid form.

As a powder it would probably make some interesting mutations in your family

Peter

[rcavictim]

The 416B is a microwave amplifier tube used primarily in now defunct Northern Electric TD-2 point-to-point microwave systems by the telephone company operating around 4 GHz (C-band). The very high frequency potential of this tube is not necessary in audio circuits and may cause the tube to oscillate and annoy NASA.

I used to have the cavities and was experimenting with these tubes back in the emerging early C-band satellite TVRO days. I succeeded in watching HBO and Cinemax through them but the noise was very, very high.

It is true that they contain berillium oxide. You do not want to inhale that.

[EC8010]

Beryllium oxide is extremely toxic, so you won't want to go crushing the valve. Other than that, the 416D is safe.

You need to take care electrically with 416D as it is extremely fragile. A constant current heater supply is probably best (have a look at the data sheet). I've tested this valve on the bench and it looked quite promising. My 350MHz Tek 485 didn't see any RF oscillation and there weren't any odd effects that suggested oscillation at a higher frequency than my oscilloscope could see, so it's a "potential audio type."

[serengetiplains]

Richard Sears has toyed with the 416B/C as a phono preamp tube. His comment on the tube, taken from his website is:

Sonically, the 416 seems to be a terrific choice for low-level phono signals permitting absolutely astounding resolution and I am very pleased with it. However, I did have to select units for gain, current and noise. There was a great deal of variation in the dozen units I have. THE CAVEAT IS: They were used, unused units may/should be much better. Since then I have obtained some new 416Cs and they are, indeed, much better.

[7N7]

Yes I have some of these; only the 416D contains the beryllium oxide. The boxes say: "return to WE" - not much chance of that.

Amazing things: the grid wire is 0.0003" in diameter and the grid is wound onto synthetic sapphire pillars and is fixed about 0.0006" from the cathode surface. The grid wire was produced electrolytically and gauged by measuring the resistance during the process. 1950s high-tech at its very best.

Note I did some curves for these; they are a bit tricky - my conclusion was that it's not worth bothering with the Bs - use the Cs or Ds as they can stand a higher voltage which is actually very useful when trying to find a sensible operating point.

Also give consideration to the fact that they get very hot; I devised two aluminium alloy plates that clamped to the valves to act as a heatsink - originally the valve - designed to operate at 3GHz - was designed to screw into a waveguide.

As far as I remember I used an infra-red LED to give the bias I wanted - about 0.9V I think.

I cannot upload an Excel file so I've copied it into PSP as a .jpg but half the gridlines have disappeared. You will see that you have to run a few watts (it is rated at 15W hence the heat) to get results.

7N7

[serengetiplains]

Thanks for the info 7N7. Do you by the way know where a person might acquire some 416Cs or Ds? Sapphire, wow, what construction.

[7N7]

Originally posted by serengetiplains
Thanks for the info 7N7. Do you by the way know where a person might acquire some 416Cs or Ds? Sapphire, wow, what construction.

I think the best thing is if you e-mail me off-line - I might be able to help.

7N7

[7N7]

I suppose I should explain that I was planning a RIAA stage, using 416Ds and a pair of globe 37s(!). I did a lot of work and spent too much money on this - yet another of my half-finished projects. As EC8010 wrote, 416D looked very promising; loads of gain, only 2nd harmonic distortion etc. However it does have to be handled carefully as one might expect - and one can also expect some variation between examples.

An example of my approach may be seen in the attached photograph which shows my aluminium-alloy mounting for a pair of 416s; this was precision machined and is clamped together with three cap screws. It is drilled also to accept a large finned heatsink. The brass ring on the left of the picture is one of two I had made to screw onto the anode connection; I had to buy a tap (40 TPI) from California to get this done.

7N7