[sdiy] Help with thyratron metronome - NOT A JOKE !!

[TooManySynths]

Hi All,

Several have offered to help, thanks.  Here's my best
attempt at an ascii schematic.

                                        NE1
                2D21                    ||
                ,-----------------------||--
110             . .  |     |      |        |
---------------|. . [      |      |        \
      |         . .        |      |        / R6
      /           |        C||    /        \
      \ R1        |        C||    \R5      |----
      /           |     L1 C||    /<-      |    |
      |           |        C||    \  |     \    |
      |           |        |         |     /  -----
      /  R2       |        |         \     \  -----C2
      \           |        |         /     /R7  |
      /<- / \ / \--      -----     R4\     |    |
      \     R3           ----- C1    /     |    |
      |                    |         |     |    |
110   |                    |         |     |    |
-------------------------------------------------



Ok, first some basics.

R1 Controls the tempo
R5 seems to be a calibration control
NE1 is a neon bulb, I can't remember the correct
schematic diagram for a neon bulb
The screen grid is connected to the cathode
L1 is an electromagnet that draws a balsa wood
diaphram near it to make the metronome sound.
NE1 coincides with the click
the voltage accross L1 is higher when the NE1 is light
and you hear the click.
Both caps are .47 mf
the filaments are connected through a 6.3 v stepdown
transformer, I didn't think that was necessary to
draw.
The 110 is AC, other than the transformer and ac
switch, the schematic is complete.


I know this circuit is simple but, well, yeah I really
don't get tubes at anything be the most basic of level
of understanding.  I've read eric barbor's page and
realize that the thyratron works like an SCR.  I am
guessing that, like an SCR, feeding AC into the
thyratron is a key component to making this circuit
work, iow, the polarity reversal is what causes the
thyratron to open back up after it is turned on by the
timing circuit. But, that's about as far as I get.
Tubes are hard enough, but throw in that pesky AC and
get lost quickly. I seem to remember something about
the behaviour of neon lamps that I think it is an
essential part of the circuit, but again, it's just
all vague memories of too many hours spent perusing
the ARRL handbook as a teenager.

To start with, what is the sequence of events that
causes the thyratron to turn on and off?  

Respond in private if you wish. Let me know if the
resistor values are essential to understanding what's
going on. 

Thanks
Daryl




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