On 24/06/2012 16:06, Carl wrote:
> ----- 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
>
I have some SHV and MHV connectors that appear to be designed for RG59
and others that will take RG58. I use the latter with RG400 1/4" PTFE
coax on my 8877 amps - over 10 year's service with no issues.
Mike G8TIC
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