Plate supply grounding/metering

[K8DI]

I'm working on getting an amplifier I bought a while ago operating. It's a Hallicrafters HT-45, which was designed/sold with a separate power supply. I got it without the power supply, so I've built one up. The power supply is working. While modifying the amp's interconnections (3kV on a Cinch Jones connector...not doing that, installing an SHV connector instead).  I realized that in order for the metering to work, the B- has to float.  I built the power supply with the B- connected to chassis. I can easily modify that aspect, but I am concerned about the safety of having the plate supply floating off chassis. The negative rail is just as dangerous if the positve were to fail shorted to the chassis.... 

I recall seeing methods to 'float' the B- for metering but still have some degree of safety, but I need more details or a link to figure out how it works....  can someone explain for me?


Ed

[DMOD]

Tom Rauch has some pretty good explanations:

https://www.w8ji.com/metering_amplifier.htm

See the diagram under

Grounded Grid Amplifier Metering with Grid Meter



Phil

[KD6VXI]

Best method I've found is to float the ground side of the plate supply a couple ohms from ground (the metering system in the amp will dictate how much).  Then, take a couple 6A10 or larger diodes in series, then run them back to back (IOW, make a 1.4 volt diode out of two series diodes, and put another series set anode to cathode) across the float resistor.

That should clamp the float.

You still ground the case of the amplifier and the case of the power supply, so they are safe.  You need to run a separate B- lead from the amp to the power supply, usually connected to the bottom of a meter stack, as w8ji shows in the page Phil shared.


--Shane
KD6VXI