On Fri, 23 Jul 2004 15:05:40 -0400 Will Matney <firstname.lastname@example.org> writes:
Hi Gene & Will,
> Yes, that can be done easily. However, not having the safety of the
> isolation from a transformer can be hazardous. The chassis would have
> be grounded to the line ground. The problem is that in some older
> the outlets may not be grounded or even hooked up backwards!
> This being the case, if someone would be touching the chassis then a
> possibility of electrocution would be present.
Especially when one goes to hook up the grounded antenna lead to the
Please don't misconstrue that I in any way recommend this topology but,
theoretically, a "power good" (hot,neutral,gnd) circuit might prove
useful. It could inhibit a double pole power relay, that switches both
hot & neutral wherever they are, and/or activate an audible warning.
> Ok, now to how it could be done. Using a simple series pass transistor
> regulator could be made.
Not a great idea. Lots of dissipation incurred. And when (not if!)
the pass transistor fails full line V would end up on the pricey RF
transistors. A crowbar circuit would be a must.
> The hot lead being rectified and regulated with
> the ground going directly to the chassis and line ground.
A bad idea as noted a couple paragraphs above.
> Last, an isolated chassis might be thought of. The regulator being
> 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
> 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
> faulty outlet. So, for personal applications it may be ok, but for
> commercial applications with liability, it would be a big NO-NO!
Nothing protects against the happenstance of: missing ground, reversed
hot/neutral. If there is any path from the line to the chassis, it is
going to hurt!!!
If the entire amplifier/power supply assembly is "floated" inside a
grounded cabinet and then fed by RF input and output transformers it
would be as fault tolerant as a typical design.
> Will Matney
> From: "Gene Bigham" <email@example.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?"
Unless you are trying to fit a specific space, 48 volts is a fairly
standard power supply voltage. One can find surplus switching power
supplies up to 2KW capability with single phase AC power or more with 3
73 & Good morning,
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