[Amps] Coax for MHV connectors?

[Mike Tubby]

On 24/06/2012 20:41, Ian White GM3SEK wrote:
> Bill Turner wrote:
>
>>> 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.)
>> I agree but I would not depend solely on the single ground in the HV
>> wiring which may be relatively fragile.
>> In my amps I use a separate, heavy ground wire, and since all my amps
>> and power supplies (so far) have an AC cord with the third wire ground,
>> this also performs the function of grounding the chassis together.
>>
>> Redundancy may save your life.
>>
> I completely agree.
>
> The most dangerous situations are often when the amplifier and HV supply
> are powered up with temporary connections for fault-finding. In that
> case, there may not be as many redundant ground connections as intended.
>
> Coaxial HV cable is the ultimate assurance that if HV+ is connected -
> even if it was completely unintentional - there will automatically be a
> ground connection too.
>
> Any recommendation for super-insulated single core HV cables and single
> pole connectors is totally missing that key point.
>
>

Completely agree also, which is why my amps and HT packs use the 
following arrangements:

* RG400 with MHV or SHV connectors for B+ (also provides first ground)
* RG58 with TNC connectors for B- (also provides the second ground)
* 1K 25W pull-down between B- and GND at the HT pack end
* 220R or whatever the amp design calls for between B- and GND at the 
amp end
* third safety ground wire between radio, amp and HT pack, i.e. big 
wing-nuts and coax braid
* finally earth lead in 3-wire mains leads

this arrangement has served me well for over 10 years and has no SPOF 
(Single Point Of Failure).

In my station(s) I always use:

     MHV or SHV for B+
     TNC for B- (return) - never for RF
     BNC for low-level RF
     N-type for high level RF

I also use Ian's Triode boards or my own control circuitry that outputs 
24V DC from the amp via a control cable (4-pin XLR so its doesn't mate 
with anything else) that means that the amp is in control of the HT pack.

I have several different amplifiers 8877, 3-500, etc. that are 
interchangeable with the HT packs because they all use common connectors 
and cables.


Mike G8TIC