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Re: tube advice needed

Subject:   Re: tube advice needed
  Date:    Tue, 20 May 1997 18:45:29 -0500
  From:    "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To:    Tesla List <tesla-at-pupman-dot-com>


> Date:          Mon, 19 May 1997 13:03:45 -0500
> To:            tesla-at-poodle.pupman-dot-com
> Subject:       tube advice needed
> From:          Tesla List <tesla-at-pupman-dot-com>

> Subject: tube advice needed
>   Date:  Mon, 19 May 1997 13:19:41 +0000
>   From:  STEPHEN SE CRAWSHAW <SE-CRAWSHAW-at-wpg.uwe.ac.uk>
>     To:  tesla-at-pupman-dot-com
> 
> 
> Dear list, especially tube gurus,
> 
> I went to a car boot (trunk?) sale yesterday and happened upon a
> guy selling two very large radio valves. Unfortunately the guy in
> front of me bought them both for five pounds the pair. I was
> gutted. However, on questioning the seller, he informed me that
> he has about 9000 - that's right 9000 tubes at home, many from
> old radio transmitting stations, some military. He said he has
> some that are about 1 metre tall and water cooled, hopefully he
> will have some other neat stuff too.
> 
> I am going round to this chaps house soon, and I would like to
> know the numbers and types of the most desireable large tubes for
> TC work. My electronics background is 1983 onwards, so I am
> almost totally ignorant about tubes. However, this opportunity
> sounds too good to pass up, so I am going to buy some tubes in
> the event that I have time to try them out. 
> 
> Could tube guru's list their all time favourite tubes, valves,
> triodes, tetrodes etc.? I am especially interested in devices
> which will not require too much additional circuitry, i.e. direct
> replacements for spark gaps (thyratrons?).
> 
> Thanks for your help, I'll let you know what this yields
> 
> 
> steve crawshaw
> 
 
Steve,

I only have personal experience with a few types.  You have to know 
what power range coil you want to make, obviously.  Rule number one, 
if given a choice, ALWAYS look for a triode.  Pentodes and tetrodes 
can often be made to work, but the job involves making extra 
circuitry and a lot of dinking around.  Triodes are what you really 
want, period!

For small coils 811-A's are OK.  They are slightly too small 
(electrically fragile) for use with a 2000 volt domestic microwave 
oven xfmer.  They come out of the box with a 1500 volt max plate 
voltage rating.  Four 811-A's will produce a 14 inch brush discharge 
while almost melting.

810's are great.  You can parallel as many of these as you want, and 
they will handle 2500 volts on the plates at 175 watts dissipation 
each.  I made a 1000 watt RMS output coil out of 3 of these.  This 
coil makes a reliable 18 inch brush discharge.

833-A's are a terrific medium sized vac tube TC tube. Plate voltage 
rated at about 3 kV with 450 watts plate dissipation as I recall. They
are 
roughly equivalent to three 810's.  You can use multiples of 833-A's 
on a 7000 volt pole pig at slightly reduced voltage (variac power 
control implied). 

If you want to get into *big* power look for triodes employed in 
commercial broadcast transmitters.  I built my Coronatron based on 
three EEV BR1160 triodes (5 kW plate dissipation each) in parallel.  
This puppy has only been pushed to 6.5 kW because of a tiny plate 
transformer currently installed, but at just 2800 watts it is almost 
scarry.  My total filament power is 1.2 kW alone!  I hope to 
*discover* the capabilities of my Coronatron later this year.  I have 
a hunch its gonna be an outside job. : )

A terrific ceramic tube from the broadcast industry for very high 
power are the 3CX- series.  For example a 3CX10,000 or a 3CX15,000.
There is a letter code exponent at the end of this part number which 
signifies fillament connection I believe.  Again running from grey 
cells, a 3CX10000D is a tube which plugs into a really expensive 
socket, but the 3CX10,000-A7 has flying leads for filament with 
eyelet terminals. These are ceramic tubes with finned external block
anodes
rated at 10 kW and 15 kW respectively.  These run at up to 8 to 12 kV
plate 
voltage, but can operate fine and give a lot of Tesla coil power at 
lower voltages.  Hell, you could run one off a domestic microwave 
oven transformer (2kV-at-~1 kW) but your filament power would be a large 
competing number to your plate input.  

A tube that works well at microwave oven transformer voltages is the 
805.  Use one or two in parallel. (I used one in parallel once, this 
is easy to do actually but hard to picture).  Just kiddding. : )

One of these daze I'm gonna build a vaccuum tube TC with a tiny tube 
like a 6SN7 with the two triode sections parallelled.  This 7.5 watt 
tube shud be good for 20 watts in Tesla mode.  

Just some ideas.

rwstephens