[Hallicrafters] More on solid state rectifiers

[David C. Hallam]

Is this a real problem or a perceived one?

I understand that in the case of a high voltage linear supply with lots of
filter capacity in rush currents can problems without some delay but that
delay only has to be for a few cycles of the AC line.

If there is a 1 1/2 to 2 second delay, what's the problem?

David C. Hallam
KC2JD

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Craig Roberts
Sent: Thursday, December 09, 2004 2:43 PM
To: hallicrafters
Cc: ke7kk at earthlink.net
Subject: [Hallicrafters] More on solid state rectifiers

Hi again,

On the topic of possibly damaging inrush currents being unleashed when
substituting solid state devices for tube rectifiers, here's when Ted
Weber himself -- maker of the luxurious Weber Copper Cap -- said a few
months ago. He's talking specifically about using them in Collins 516F-2
power supplies, but the same principle applies elsewhere.

73,

Craig
W3CRR

Ted says:

"The tube rectifier has around 8 seconds of warm up time. Since the
internal
resistance of the tube is high until the tube is warmed up, the B+ rises
slowly as it charges the HV filters. At that same time, the other tubes are
also warming up. When they get up to temperature, they provide a load that
drops the B+.
So, the long delay of the rectifier warmup prevents a high voltage B+
condition on the other tubes in the rig until they warm up. Our copper caps
have an inrush themistor that has a negative temperature coefficient,
and as
the B+ current increases, its internal resistance decreases. Hence, it
has a
warmup time like the tube rectifier. However, the warm up time of our
Copper
Cap is only about 1-1/2 to 2 seconds, depending on the current draw as the
filters charge. Bottom line is, with the C-Cap, the B+ might ramp up higher
than some may be comfortable with until the other tubes warm up and pull
the
B+ back down to normal operating level."
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