[Amps] Tube regulators
Will Matney
craxd1 at ezwv.com
Fri Jul 23 15:05:40 EDT 2004
Gene,
Yes, that can be done easily. However, not having the safety of the
isolation from a transformer can be hazardous. The chassis would have to
be grounded to the line ground. The problem is that in some older homes,
the outlets may not be grounded or even hooked up backwards! This being
the case, if someone would be touching the chassis then a ground, a
possibility of electrocution would be present.
Some years ago, a manufacturer out in California made a sweep tube amp
which was transformerless. He used a quadroupler circuit to obtain the
high voltage and ran the tubes grounded grid. It worked, but if the
chassis wasn't grounded, a possibility of a 975 Vdc shock would be
encountered. Needless to say, the design didn't go over very well.
Ok, now to how it could be done. Using a simple series pass transistor
regulator could be made. The hot lead being rectified and regulated with
the ground going directly to the chassis and line ground. A simple zener
diode controlling the base of a series transistor would regulate the
voltage. A potentiometer could be added here also to vary the voltage or
a stepped zener string. To get the high current needed for PA's. the
series pass transistor can be paralleled and a driver be used which
would be controlled by the zener. Basically, it's the same circuit found
in all the electronic books including the ARRL handbook.
Last, an isolated chassis might be thought of. The regulator being built
upon a chassis or pc board which it's ground was not connected to the
chassis. If the chassis was then grounded and if a possible leak to the
chassis happened, the line fuse should open. This could be done with an
amplifier too if the DC ground was connected to the chassis with
suitable capacitors allowing only RF to be there for shielding and
connection to the coax. I played with some circuits such as this with
success but that was long ago. The problem is that whatever the power
supply is running could still have voltage on its chassis due to a
faulty outlet. So, for personal applications it may be ok, but for
commercial applications with liability, it would be a big NO-NO!
Will Matney
From: "Gene Bigham" <jbigham2 at kc.rr.com>
Subject: [Amps] Tube regulators
"With all this discussion about tube regulators I have a question. Is
there a cheap way to make a direct AC mains supplied power supply for
approximately 48 to 50 volts DC for a solid state amplifier using some
type of regulator off the 110-120 volt AC line? I keep wondering about
rectifying the 110-120 volts AC and then using some form of a regulator
for the high current 48-50 VDC required?"
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