[Heathkit] SB620 sweep cont'd

[W2HX]

You cannot replace the neon. It is, in fact, essential to the sweep. As the
voltage across it increases, so does the horizontal deflection of the beam.
Once the neon reaches its breakdown voltage, the sweep goes back to zero to
start again.

This is my understanding of the circuit, I am sure others can elaborate (and
refute!)

73 Eugene W2HX

-----Original Message-----
From: heathkit-bounces at mailman.qth.net
[mailto:heathkit-bounces at mailman.qth.net] On Behalf Of Michael Tortorella
Sent: Tuesday, January 12, 2010 6:15 PM
To: heathkit at mailman.qth.net
Subject: [Heathkit] SB620 sweep cont'd

G'day all,

Thanks to all who replied with suggestions on the above.  I did some voltage
checks on V3, the sweep tube, and all are about 20% low.  Hmmm.  I had
replaced the neon pilot light with an incandescent, driving it off the B+
line with a 27k resistor in series.  Is the neon bulb essential to the sweep
circuit?  It doesn't look like it is, but maybe the current drawn by the
pilot light is pulling the B+ down?  

Thanks in advance and 73

Mike W2IY

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