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Re: VTTC from Eimac 8755 on eBay
Original poster: Frank <fxrays@xxxxxxxxxx>
Growing up with tubes and old ham operators, a lot of the lore has
been lost today.
WAAAY back when it was common to put a thoriated tube in a set and
run it in without plate or screen voltages to bring the emission up
to normal standards. This was recommended by the mfgrs on new tubes
believe it or not!
Used tubes from commercial stations and became weak and were
replaced. Those were the ones hams could afford, usually free. To
make them useful they did that or elevated the filament voltage. Of
course the tubes were not in continuous service so they worked fine.
Back them the stations were AM and a full KW.
Many links have already mentioned this but I just had to say it was
nice some people still remembered how to make tubes last!
as tubes and frequencies evolved, the plates and lead in's shrunk.
For a VTTC coil, you will be operating in the ! MHz range or the
really good coil should be around 200 KHz. The tubes to do this
should have the largest plate size possible. A graphite plate is
still the best for a lot of power and abuse. You just tune them for
minimum red on the plate.
Spark length is usually proportional to watts, the more watts, the
longer and fatter the sparks.
A good set of tubes can run on a plate of 1KV at 1 amp, that is !KW
in gross terms. To get a transistor to do the same, you would need to
have 50 amps at 24 V for example. That is a BIG transistor and heat sink!
SSTC's do just about the same by dumping 10-20 amps into a primary at
110. Even those devices are big and require decent control circuits.
a VTTC is simple in comparison, just a few resistors and caps.
Quiz answer: A monode is a light bulb?
Thanks!
Frank
At 12:14 AM 2/5/2007 -0700, you wrote:
Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
At 03:13 PM 2/4/2007, Tesla list wrote:
Original poster: westland <westland@xxxxxx>
I didn't know you could do that with a transistor (any specific type?)
Haven't done it in more than a decade.. (obviously, you need a metal
can type transistor, and those are somewhat unusual these days of
TO92 plastic packages)... I've done it with a 2n404, a 2n1613, and a
2n2222, thereby dating myself, since I doubt one could buy a 404 or
a 1613 these days.
And, some 15-20 years ago, people used to make cameras by using
static rams with the cover knocked off. Certain parts from Micron
were favored for this, because the pixel (ram cell) layout was easy
to figure out, and they had the right kind of buffers so you could
sneak an analog output, after a fashion.
but ... yeh ... why not deconstruct a mass market device ... you
know it's going to be priced at the marginal cost of production
(which means that all the R&D and last minute sweating by the
engineering group to actually get a production version of the
device has been priced out at pretty close to zero) ... there's
no way you could compete with your own device.
But it may be a bit upsetting to the Varian engineer that designed
the anode of the 8755... nobody wants his work
Actually, they don't mind much... tube design guys and gals are
used to this sort of thing. You make new tube designs by taking the
gun from one tube and the anode structure from another, etc.
I think they'd actually be happy that someone is actually using a
thermionic device of any kind, since it's a dying art, and they're
happy to have someone carrying on the flame.
(Quick tube guy joke/question.. we all know about pentodes, diodes,
triodes, etc... do any of you have a monode at home?)