[AMPS] Re: Surge voltage, HV connectors.

Wilbert Knol w.knol@niwa.cri.nz
Fri, 3 Mar 2000 08:43:28 1300


Thanks to Tom W8JI, Han SM5KI and Gerard VE5FF for the feedback.

Gerard suggested Kings Electronics 1705-1 and 1707-1 plug/connector 
pairs. I am in the process of getting some more info from Kings.

After Tom's comments on the Millen I won't persue that any further.

> >Microwave oven transformers have horrible ESR, and make very 
> >poor linear amplifier power supplies.

Measured:
2093 VRMS (no load)
2038 VRMS @ 400 mARMS (projected amplifier load)
I can't see what's wrong with this.

The fact the supply under test sags, is not due to poor regulation. It is simply 
a result of the fact the capacitor will float to Vpeak under no load. I note that 
all HV supplies in the 1990 ARRL handbook are of this type. All will exhibit 
voltage surging under light loads.

Voltage surging can be reduced by using an inductor, and by increasing the 
stand-by load (more bleeder current). Inductor-input filters don't seem to be 
used in the commercial designs I have seen (FL2100, AL811). I would prefer 
not to increase bleeder current (a crude form of shunt regulation) but will do 
so if I have to.

What I wanted to know is: is this voltage surging really a problem? When I 
put the key down, the supply will 'collapse' to its working voltage of 2.1 kV. If 
I tune up the amplifier for steady-state clean output (no flat-topping) at 2.1 
kV, will the initial reduction from 2.8 kV at the start of the transmission 
cause non-linear distortion?

If the answer is 'yes', what should I limit the surge voltage to?

> >> 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.

The mains here is of the Multiple Earthed Neutral type.

Mains and HV are mixed inside the amplifier anyway. I can't see how 
combining mains, interlock and HV in one properly rated cable would make 
things more unsafe. In the case of a short from B+ to mains neutral, the HV 
supply would be unable to lift the mains supply. The resulting short would 
cause it to blow a fuse.

I can see separate cables would be marginally safer (even though they will 
probably be tied together in one bundle afterwards). 

> >Use a decent separate interlocked HV connector
Any suggestions of what type of connector to use?

> >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.

Good point. Also thanks for the suggestion to use grounded, armourd cable 
and a grounded connector shell.

Wilbert, ZL2BSJ



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