On 6/23/2012 11:35 PM, Ian White GM3SEK wrote:
> Jim W7RY wrote:
>> I use RG59 on mine. Works with 4KV and has been for years.
> Same here. I suspect those voltage ratings are for square-cut open ends.
>
>
>> -----Original Message-----
>> From: Jim Barber
>> Sent: Saturday, June 23, 2012 3:39 PM
>> To: Amps@contesting.com
>> Subject: [Amps] Coax for MHV connectors?
>>
>> I need to make up some MHV cables for a 4KV 2A max DC supply, (both B+
>> and B-) and I made the mistake of looking up the voltage ratings for
>> RG-58, RG-59 and LMR-240 cables, all commonly used with those connectors:
>>
>> RG-58 1900V
>> RG-59 2300V
>> LMR-240 1500V
>>
>> In a word, yikes! RG-59 has the highest rating, but I like it the least
>> for exposed cables because of the solid center conductor
>>
>> The connectors are rated at 5KVDC, but what cable type? It seems like
>> every time I think I know something... ?
>>
>> I'm tempted to give it up and machine my own bulkhead pass-throughs out
>> of acrylic and use HV cable instead. In fact I would have already except
>> I'd really like the cables to be detachable.
>>
> More important is that the connectors include their own chassis ground
> connection, and the coaxial cables will very probably short-circuit the
> supply if damaged.
>
> What you must NOT do is allow a situation where an isolated amp chassis
> can be connected by a single HV+ lead with no ground return or HV-minus.
> (Welcome to the wonderful world of single-wire Millen connectors.)
>
> And let's say it again: MHV connectors are a poor design which fails on
> too many important safety points. That is why it was necessary to invent
> the SHV connector.
>
> Search the AMPS archives for "SHV" to see the rest of the story.
>
The only reason for using MHV over SHV is price. I can get quality,
Western-sourced MHV connectors for $13 USD and SHV from the same sources
are $42 USD. But you're right, SHV are safer and can't be mistaken for
BNC connectors. It's difficult to *not* use Chinese connectors, though,
when I can get decent-quality nickel-plated male SHV connectors with
gold pins for RG-6 from Shenzhen in small quantities for $5 USD each or
so including shipping.
As for the "hot chassis" issue, this particular design keeps B- only far
enough above ground to be able to meter grid current, 6A safety diodes
are included at each end and the PS and RF decks are ground-bonded
several different ways. Digressing a bit, if I knew of a way to
conveniently, accurately and simply meter grid current without holding
the cathode above ground I'd jump on it... I've tried Hall Effect
current transducers, but don't care for the additional complexity of op
amps and associated power supplies, shielding, bypassing etc.
Back on topic, I'll just stand corrected and use the Chinese SHV
connectors and RG-6. I'd rather use TE/AMP, but they've priced
themselves out of my market, at least.
73,
Jim N7CXI
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|