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Re: [Amps] Single Supply, multiple Amps switching

To: "'N7EME'" <>, <>
Subject: Re: [Amps] Single Supply, multiple Amps switching
From: "Jim Garland" <>
Date: Fri, 11 Nov 2016 05:36:07 -0700
List-post: <">>
Hi Jerry,
Using a single HV power supply with multiple amplifiers is a bit more
difficult than one might at first imagine. Modern amplifier design routes
the B- return separately from chassis ground, and avoiding interactions
among the metering for the amps can be tricky.  There are also potential
safety issues with routing HV simultaneously to different amplifiers,
especially if an amp chassis becomes ungrounded. Cathode bypass caps also
have to be rated for the full HV, if the return path to B- is left open.
Tetrode amps are a bit more problematic than triode amps.

A few years ago I designed two HV power supplies intended to be used with
three amps each. One power supply provides about 2600V (for 3cx800s) and the
other about 4400V (for 8877s). I used HV vacuum relays to switch the HV
between amps, and PCB-mount relays to switch the low voltages. A logic
interlock prevents two amps from being on-line simultaneously. The design is
published in QEX, but I'll email you a copy separately.  The power supplies
work very well, but the design may be a bit more complicated than you're
looking for.
Jim W8ZR

> -----Original Message-----
> From: Amps [] On Behalf Of N7EME
> Sent: Thursday, November 10, 2016 04:21 PM
> To:
> Subject: [Amps] Single Supply, multiple Amps switching
> Hello All,
> Just joined the group and have a question concerning switching multiple
amps with one
> supply.
> I have a single Peter Dahl xfmr that I designed a power supply with and
want to use it with
> multiple amplifiers. 1175VAC @3 amps with a doubler giving about 3325VDC.
> I have a 6 meter GS31B G-G amplifier currently running on that supply, but
have plans for
> 2 meter and 70cm G-G amps using GS31B's as well.
> Between the power supply and the amplifiers, I have a control panel that
switches the Plate
> Current meter, Grid Current meter and a PTT enable line, that gets
grounded for each
> amplifier when selected. Filament is supplied by individual xfmrs in each
amplifier and is
> floating above ground, no center tap, etc...
> BUT.... I will have the High Voltage always present on each all the tubes
after a 3 min
> timeout, and the Filaments and Blowers will be running on each tube. Any
amp currently
> selected by the control panel is bias off  at about -56 volts until the
PTT line for that tube in
> enabled. Resting current is adjusted for 100ma of Plate current when idle.
This much works
> great right now with the single 6 meter amp.
> My question is, can I apply Plate voltage along with just the Filaments
and Blowers on a
> tube, and have the Cathode and Grid metering open, and not cause any
> I believe I can because there is no current path for Cathode current or
Grid current for the
> un-selected tubes. I need additional confirmation from someone with a
little more
> knowledgeable than myself on such matters
> 73
> Jerry Mulchin - N7EME
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