[TCML] Sidactors in a can of worms

[Finn Hammer <f-h@xxxx>]

I got the Sidactors yesterday, Thanx Terry, and immediately took action 
to measure their break over voltage.
Something soon seemed odd, they looked like TVS'es to me, not sidactors 
at all.

When I applied voltage across them from my current limiting bench 
supply, a HP6255a, the devices did respond to break over voltage, but 
failed to break over to a near short, as advertised by Teccor, and as 
previously experienced by the KxxxxF1 series that we have been using up 
to now.
What I saw was a device that plainly clamped the voltage to the break 
over level, and kept it there.

This is the behavior that I`d expect from a Zener and a TVZ, but not 
from a Sidac.

Of course, there might be a limitation of my measuring approach that I 
had overlooked, holding current came to mind, so I decided to lash up a 
birds nest SISG, to test out the new types against a known good one, the 
K2500F1, which has shown a consistent break over voltage of 135V per 
section.

The K2500F1 single section worked as expected and produced this 
oscilloscope trace:
http://www.hammertone.com/temp/sidac.jpg
In this screen,
http://www.hammertone.com/temp/sidac.jpg
Top trace, cyan CH2, is gate voltage, 15.2V
This is a bit low since generated from a 24V TVZ, but the current is low 
too, as seen on 3rd trace.

2nd. trace, magenta CH3, is current into gate, measured with Tektronix 
P6022 current clamp and passive terminator.
1.36A into gate.

3rd. trace, green CH4, is current in tank circuit, 17.8AP-P measured 
with Pearson Current Monitor #101

4th trace, Yellow CH1, is voltage across tank cap., 135V
Screen says 62V but probe is MX9003 differential by Metrix in 200:1

So far so good.
But when I plug any of the following sidactors into this circuit, all I 
can record is that the voltage across the cap rises to, and stays at, 
break over voltage of device.
What I don`t see is any rapid discharge of tank capacitor, no voltage 
rise on, or current into gate, and thus no oscillations.
So as far as I can see, these Sidactors are not what they are advertised 
to be, but instead TVS, Zener whatever derivatives unsuited for SISG duty.

I`m at my wits end with this, because -frankly- I feel out of my depth 
claiming this in the face of a major manufacturer like Teccor.

I guess I's time to write them, but I'd just bring it up here first.

Cheers, Finn Hammer

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