[Heathkit] SB620 sweep cont'd

[Mike McCarty]

john wrote:
> That's right. A relaxation oscillator.
> 
> http://www.oberlin.edu/physics/catalog/demonstrations/em/neonosc.html
> 
> A clever use of a mundane part. :-)

My first thought, when I heard "neon lamp", was the same. However,
looking at the schematic does not support that. It is being  used
solely as a regulator, I think. It is a voltage regulator stabilizing
the swept (not sweep) oscillator, but it is not an oscillator itself.

The swept oscillator is V2B. The neon is fed from a low impedance
point in the power supply, and has no parallel capacitance to discharge.
There is a capacitor nearby, but it is used simply for decoupling
along with R12 to keep out high frequency noise.

The lamp which _is_ used as a relaxation oscillator is a different
lamp, not the one used for the power indicator. That lamp is near
V6A and is used as the sweep oscillator. It is, as one can note,
in parallel with a cap which it discharges. This is the sweep
oscillator. Different lamp, however. That lamp provides the
sweep control to the swept oscillator V2B.

Mike
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