[Amps] Tube regulators

[Will Matney]

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?"