Paul, I don't believe there is any reason to treat a B- return as if
it were a B+ lead. With your planned diode clamps, B- will always be
within a few volts of chassis ground. Running a separate B- cable,
with its own connector, is potentially a dangerous situation. In some
circumstances, unplugging the B- connector could raise the entire RF
deck up to the B+ potential. In my opinion, it is far better to run
the B- wire in the same cable with the other control wires, so that if
the main control connector is unplugged everything safely shuts down.
Sent from my iPhone
> On Mar 12, 2014, at 4:55 PM, Paul Christensen <w9ac@arrl.net> wrote:
>
> At the risk of starting a raging philosophical war, I am looking for opinions
> on how to best manage wiring between an outboard HV supply and an RF amp deck.
>
> Here's the project:
>
> An old Alpha 77D is being used as the foundation of a quasi-homebrew amp. The
> plan is to upgrade the PS and move the HV transformer and oil cap out of the
> RF cabinet and into its own enclosure -- similar to what K2VCO and W8ZR have
> done. I am doing this for two reasons: (1) I can no longer manage the
> weight of a 77Dx amp by myself. It already takes a meditation exercise to
> move my older Alpha amps from the ground and onto the desk; and (2) Ep will
> be slightly elevated with better regulation under full load. A new 2.0A CCS
> Dahl plate transformer will be purchased from Hammond. The existing
> 25uF/4KV oil cap gets upgraded to 35 uF/5KV. A dedicated filament
> transformer will be mounted in the RF deck area once occupied by the old
> Hypersil HV/Filament transformer.
>
> A new PS cabinet is being fabricated and will house the HV transformer,
> filter cap, diode stack, and perhaps a bleeder pair. I would like to use a
> SHV connector for HV, but after reading the AMPS archives, I'm seeing widely
> varying opinions on how to best manage B- I've seen everything from just
> running it like a control conductor at one extreme to using a dedicated SHV
> connector and treating it like HV at the other extreme. A 2-3 diode string
> will be used between B- and the chassis as it is now.
>
> The new amp is getting a complete facelift with a new engraved front panel,
> round 250-degree meters, and a vacuum variable cap will be used for loading.
> Dedicated metering for Ep, Ip, Ig, and filament voltage. The Pi-L section
> will be be upgraded but remain mostly the same. Bias is redesigned using a
> 3-stage bias system with the entire bias and T/R function being
> software-controlled from my S-QSK board. A matching PEP analog wattmeter
> with Bird ThruLine section has been designed and can be used either above the
> amp or remoted to a small desktop enclosure.
>
> http://72.52.250.47/images/77D_Panel.pdf
>
> As I move forward with this project, opinions regarding current trends in
> SHV/B- distribution are very welcome. Tnx!
>
> Paul, W9AC
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