> 1. The amp uses 2 x TB 2.5-300, which are rated at 2.5 kV.
> The test bench version of the supply is a setup that uses microwave oven
> transformers charging a capacitor bank. It surges to 2.8 kV (under bleeder
> load only). Under 400 mA of load (the projected total plate current), the
> HV drops to 2.1 kV. Can I expect problems with the 2.8 kV at the start of
> a transmission or should I ignore the surge voltage?
If you live a long distance from other people, and use small
antennas, a supply that sags 25% won't make you unpopular.
If you have a reasonable signal level, you will probably make others
unhappy on occasion from the IMD distortion.
Microwave oven transformers have horrible ESR, and make very
poor linear amplifier power supplies.
> 2. The HV supply will be an external, stand-alone unit. I am having
> problems locating suitably rated HV connectors. The HV connector would
> have to be a two pole type, making B- before making B+, and rated at >2.8
> kVDC (to prevent the operator from being electrocuted)
You might consider armored cable with a grounded metal shell,
and using the second pin in the connectors as an interlock to
prevent HV from being activated unless the HV lead is connected
and the chassis are grounded together.
BTW, and fault protection resistors belong in the HV positive lead
down in the power supply, not up in the RF deck. That way if the
HV lead faults against your pet cat who happens to chew on the
HV lead, it won't blow his teeth out.
> The ARRL handbook mentions Millen 37001 HV connectors. Are there any
> places that sell these (or other suitable connectors) mail order in small
> quantities? Are the Millens any good for what I want?
The Millens, if they are the connector I am thinking of, are absolute
junk. They break easy, they allow contact with HV lead, and they
have a tendency to arc through. I've seen many of them mounted
on plexiglas to prevent them from faulting to the chassis.
> Ideally I would like an HV connector with a set of extra contacts for
> carrying mains to the amplifier filament transformer as well.
Never ever do that, unless you have a death wish for you or your
family. Especially in NZ, where the power mains are not grounded.
If you ever get a fault from the HV lead to the power line, and if the
chassis is grounded, the power supply can elevate the power lines
to whatever the HV is...or to the breakdown voltage of the poorest
insulated earthing connection on the mains. That might be the
neighbor next door, leaning on her blender while cleaning her
kitchen sink.
Use a decent separate interlocked HV connector, or make it
difficult to disconnect it or difficult to forget to connect it when the
supply is on.
> considering an interlock cct preventing the HV supply from being turned on
> unless the amplifier is hooked up. This would safeguard against a live
> dangling HV connector. This requires a a pair of HV rated contacts and 5
> extra contacts
The HV chassis mount connector should be on the supply ONLY,
not on the RF deck. Then the dangling lead has zero volts, even if
the interlock system fails.
I have a two inch diameter scar on my wrist from following Bill Orr's
suggestions about power supplies, and using Millen connectors. I
had a connector blow apart (or the wire did) and the wire flew about
two feet or more and attached itself to my wrist.
Opening a pair of 60 amp main breakers via your wrist and the HV
supply is not fun.
>
> Any pointers to suitable connectors would be greatly appreciated.
>
> Wilbert, ZL2BSJ
>
>
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>
>
73, Tom W8JI
w8ji@contesting.com
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