Toshiba tubes current models

[Opcom]

Has anyone ever used any of these power grid tubes?

http://www.toshiba-tetd.co.jp/eng/product/prden.php?type=cat&search=400000500000

They are for industrial use up to 100MHz and most are well over the needed plate power ratings, but a few are hammy-size.

I never see them available anywhere and I'd assume new is out of the question even for the 800W one.

[W3RSW]

Neat.
Too bad about the low mu for these tubes.  Wish they were 200 instead of 17 or so. The 6T58 needs 7 kv to get up to scrote.  --curious to see what the tube sockets look like.
One date seems to indicate that at least the literature was printed in 2004.

[Opcom]

The highest mu was 50. I agree, the inconvenience of bias, etc. and the much more nonlinear drive load would be an issue.

[KD6VXI]

No socket.   Grids bolt directly to the chassis.

I have a 3cw30000,  same thing.   Mine has flying leads for filament connection,  the Toshiba tubes have threaded studs.

--Shane
KD6VXI

[W3RSW]

Yes I see that but the vanes seem to be isolated by the flange from the filament connections as far as having sufficient air moving around all the elements.  Looks like air moves 'horizontally' across the pins on the anode, but separate air flow on filament studs side?

[Opcom]

The datasheets are a bit oddly delivered as "php" files but can be opened in adobe reader 11 then saved as pdf.

The Mhos are given in Siemens, which are the same thing. 1S=1M.

The nice 8T30RA has the highest mu of 50, handles, and a 30Mhz rating, ok well treat it like an 813 on 10M..

- fil. 12V @ 40A except in the plate curves it says Ef=7.5VAC. I don't understand that.

- forced air for anode at max dissipation is 20m^3/min @ 40mm H2O = 700CFM @ 1.57 inches H2O (HVAC blower perhaps). at 60% dissipation only 560CFM and 0.78 inches of water needed.

- max temp of plate and seals 250 deg C.  -that is generous.

- air jacket: "TOSHIBA VT-25004" A Google image return on that provides no picture of the air jacket or chimney, but it does provide an Oompa-Loompa in the results.

The huge radiator on this tube would probably mean no bolting it in place by the grid flange, but a light weight and flexible grid plane such as cane metal could be put in place to let air flow, sans the recommended air system. It is probably supported by the air jacket.

Class B push pull:
Eb 10KV
Eg -130
peak grid to grid volts 900
Plate current 0.4 / 1.4A
max signal grid current 57mA
drive 23W
plate to plate load 10K
output 10KW
So this puts it in a reasonable discussion zone for a single tube in ne plus ultra class B RF service.

In class C RF, one can make 11KW, but the tube will work decently at lower plate voltages too. Grid dissipation is 300W, so it's a tough beast.

Zero bias operation might be possible with 6KV and a 500mA idling current or 4KV and 200mA. That is what made me look so closely at this tube. Few of the others I looked at seemed compatible with any kind of zero bias operation, but why be hung up on zero bias? A good grid tank or cathode tank should be used anyway, and a bias supply would be one of the low cost parts needed in any transmitter or amp.

It's a beautiful tube isn't it? Bet it's partly hand made too, perfection and craftsmanship.

[W3RSW]

Yes it's gorgeous and check out those love handles or are they 144 radiation neut. stubs? 

[K1JJ]

Yes, bias could be handled easily with zeners or regular diodes in the cathode.

A Mu of 50 is still kinda low and would take some drive in RF linear service compared to the common power grid tubes used today.

All of this is fine and good, but the big unanswered question is "how clean is the tube itself?"   Most of the time we need to dig for IMD figures. Manufacturers will sometimes reluctantly send them out if pressed.

It takes extreme manufacturing precision and great designs to put out IMD numbers that are above -30dB 3rd order in RF linear service.  This includes class B modulator service.    Class C is another matter and not as critical.

Before anyone gets serious about these tubes, search out actual amplifier engineering tests by the company showing these critical figures.

It is not easy to equal an 8877, YC-156 or 3CX-3000A7, all of which were designed for high amplification and extreme cleanliness approaching and exceeding -40dB 3rd IMD figures in RF linear service.

My point is that the tubes may be cheap, but if we are to spend a lot of time and money building a FB amplifier, then make sure we have the best tubes available for the job. It may cost a little more, but WTF.

BTW, do you realize my whole shtick above is negated simply by running an SDR Apache using pre-distortion software?  Linear amplifiers can now be dirty, but cleaned up with this technique...

T  

[Opcom]

I do greatly appreciate that system approach.