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Re: [TCML] vttc issue power supply arcing during staccato mode
Earl,
Staccato tends to give more kickback than normal operation especially
if the switching occurs when it shouldn't... if the timing is not just
right. The pulsing should sound "solid", not "snappy". Adjust the
timing pots to give a solid sound. I'm not sure
if this will fix the problem though. I've never had the transformer
arcs in my VTTC's. In one early staccato design, the switching
transistor was burning out so I used a series choke to protect it.
Eventually I went to using a triac and later an SCR. SCR's are
more robust in general. I used a 1200V, 50amp SCR but that
was overkill. I used it because that's what I had handy.
Cheers,
John
-----Original Message-----
From: earl rhodes <earl_1975@xxxxxxxxxxxxx>
To: tesla list tesla list <tesla@xxxxxxxxxx>
Sent: Thu, Oct 4, 2012 6:54 am
Subject: [TCML] vttc issue power supply arcing during staccato mode
hi
i spent all last night sorting out my staccato for my coil tested it first thing
this morning and it does indeed work !!...but every time theres a spark or
enough voltage coming in to cause the smallest discharge there is arcing between
the primary and secondary of my power xfmrs
both of them in exactly the same place they are going between where the
filament winding for the magnetron is and the primary
it is not a destructive arc it is id say about 10 maybe 15kv by the looks of it
and it is very persistent it happens every time theres a spark
a look at the output waveform of the coil on an ungrounded probe to air it is
what you would expect really a smooth gain in voltage followed by a quick
dampening down no unusual sighns
no spark on the output but i could still hear the arcing going on on the other
side of the xfmrs so it has no effect on the output
siince the test my switching device (a mosfet) has died a quiet death due to
testing after checking out the connections to ground and checking my rf bypass
was ok which it all is and the fault was still present
so the mosfet was probably badly over voltaged but since the mosfet went and
normal operation was restored the fault dissapeared so its only happening when
the tube connects or disconnects i have no way of telling which way round it is
can anybody help
earl
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