Re: Toobz the rating game
Tesla List wrote:
> > Subject: Toobz the rating game
> Subscriber: gowin-at-epic-1.nwscc.sea06.navy.mil Wed Jan 8 22:23:42 1997
> Date: Wed, 08 Jan 1997 09:35:18 -0500
> From: Dan Gowin <gowin-at-epic-1.nwscc.sea06.navy.mil>
> To: tesla-at-pupman-dot-com
> Subject: Re: Toobz the rating game
> Tesla List wrote:
> > Subscriber: hullr-at-whitlock-dot-com Tue Jan 7 22:29:53 1997
> > Date: Tue, 07 Jan 1997 17:36:46 -0800
> > From: Richard Hull <hullr-at-whitlock-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Toobz the rating game
> > To those interested in Toobz,
> > With the arrival of John Freau ( tube coil guru) and Robert Stephen's
> > high powered monster, a lot of interest in tube coils and their variants
> > is occuring on this list.
> > For those not around during the old days, the tube must seem a bit
> > strange. Actually they are more akin to a virtually indestructable FET.
> > The most interesting characteristics of tubes is that they are rugged and
> > still available in ever decreasing numbers at hamfests for reasonable
> > prices. The day will come when tubes we take for granted today will be
> > antique and collectable curios.
> > Tubes are most often applied in Tesla coils as amplifiers sent out of
> > control to form an oscillator. This form of tube coil is interesting but
> > a proven power hog and low spark producer. John Freau's Staccato mode of
> > operation has made the longer spark tube based system a reality albeit in
> > slower pulsed mode. The Hydrogen thyratron can actually sub for the raw
> > air gap in special case scenarios.
> > The choice of a tube is all important and the ratings and specs for them
> > are confusing to non-tube folks. John Freau has a knack for running his
> > tubes far outside the spec sheets. Only tubes will allow this. Also
> > natural intermittent duty cycles associated with Tesla systems allows the
> > tube to be strained severely without immediate destruction.
> > In general, a bit of "fast and loose" can be played with the
> > specifications of these devices. For instance, the 4C35 hydrogen
> > thyratron can handle 380KW of peak pulse power, have 8KV on its plate,
> > and see as much as 100 amps of peak plate curent with a PRR (pulse
> > repition rate) of 1000pps. The recommended max on time is 4-6usec. If
> > you can live with 200pps the peak current can double. If a 1-2 usec on
> > time is used at 200pps the peak current can increased again. It is a
> > matter of balance. Learning to operate tubes wisely is an art.
> > If you are like John and I, the normal operating parameters are taken as
> > the barest starting point and the absolute max ratings column on a
> > manufacturers spec sheet is accepted as standard proceedure! Double the
> > max ratings are where we like to operate normally. This usually shortens
> > tube life by 200 to 500% or more. Thus, if a tube would normally
> > function for 1000 hours then we get only a few tens of hours. Based on
> > the frequency of use of a coil, this can be many years of operation.
> > I'll be curious as to how many here actually venture into tube systems.
> > Be prepared to hamfest for parts critical to this special area.
> > Actually, the hamfest will readily yield far more tube coil related parts
> > than disruptive parts. Very tubular guys!
> > Richard Hull, TCBOR
> I'm personally looking for a pair of RCA 573B
> power triodes or any high power 811 equiv. It seams
> these high powered triodes are still used in guitar
> amps. But most of the dealers I've talked to want
> $50 US or more for these tubes.
> Do you have any idea how much one of those
> power triodes, that Radio and TV stations use cost?
> You know, the ones that need forced air cooling
> and come in ceramic/metal casings. I've heard that
> the specs on these devices are high enough that a
> pole pig can be used as a plate supply.
> D. Gowin
I have a friend that is the engineer at the local radio station. He has
several 811 tubes and also about 200 or so other transmitter and
rectifier tubes that are all brand new and still in the original boxes. I
could ask him if he wants to sell some and how much it you like.
I know they use forced air tubes at the radio station but don't remember the
tube numbers. He told me when a tube is replaced with a new tube a chart is
made for each tube. The chart lists voltage and current and power output of
each tube. After several weeks or months if the power on a tube drops the
voltage on that tube is adjusted on the plate and grid to bring the power
output back up to where they want it. After a certain length of time the
chart will show that the tube is reaching the end of its useful life and it
is removed and replaced with another tube before the tube fails while on the
air. All the old tubes will still produce there full output rating but are
about 95% used up. With only 5% of the tube life still remaining a tube can
still be useful for all types of projects. My friend gave me two used 810
tubes. He said they don't use 810's any more because they changed over to a
different tube that is forced air cooled. The used tubes are sold very cheep
and some tubes are returned to the manufacture to be rebuilt. Rebuilt tubes
are just as good as new tubes but cost less. If anyone is interested in a
used tube I can ask what they have and how much. I would suggest that maybe
you could check with a radio station in your area and ask about used tubes.
TV stations probably have used tubes also.