----- Original Message -----
From: "Jim Barber" <audioguy@q.com>
To: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
Cc: <amps@contesting.com>
Sent: Sunday, June 24, 2012 4:42 AM
Subject: Re: [Amps] Coax for MHV connectors?
> 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
RG-6 ???
Steel core and a foam dielectric?
Sounds like a recipe for disaster to me.
Carl
KM1H
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