[Prev][Next][Index][Thread]
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