[Amps] Question about separate power supply/RF section
Ian White GM3SEK
gm3sek at ifwtech.co.uk
Tue Jan 22 17:00:40 EST 2013
Jim Garland wrote:
>No, the B- is only grounded at the RF deck, at the same spot that the
>cathodes are grounded. To steer the cathode current properly, it is
>important that the B- lead NOT be grounded at the power supply. If it
>were grounded, then you are correct that it would merely be a parallel
>connection with the other ground wires. However, a single point ground
>is what is required.
>There will be a negligible voltage difference between the power
>supply/rf deck chassis and the B- lead, because of the single point. If
>the power supply should become completely disconnected from the RF
>deck, then the 220 ohm resistor, mentioned in my earlier email, will
>keep the B- at the same potential as the power supply ground, within a
>volt or two.
Agree with all that. I just put some links on my home page to a 3-part
article and a Powerpoint presentation giving more background.
Click on "High Voltage Power Supplies - Safety by Design".
My personal standard for connecting separate HV and RF chassis is the
5-pin XLR connector, This allows completely duplicated B-minus
conductors, duplicated ground (plus the metal shell and the cable
shield) and also a switched control voltage to the contactor in the
transformer primary. Use of one multi-way connector ensures that HV
cannot be turned on unless the ground and B-minus return are also
Chassis ground bonding is an area where it's good to have backups for
the backups, so there are further ground connections through the coaxial
HV cable and also through the lower-power mains supply to the amp
chassis (heater and blower).
For the HV side it's SHV connectors - and no other.
73 from Ian GM3SEK
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