[Amps] metering HV on PAs

[Carl]

Puttin in a string of 14 1M 1/4W as used in the SB-220 replacement board 
doesnt give me much confidence either. Just the thought of having 3kV on 
the top one gives me the shivers.

Wire wound bleeders dont drift in value otherwise precision nichrome 
meter shunts would be of no use. The miniscule leakage in good caps can 
also be discounted. The days of using carbon comps for much of anything 
is long past.

Ive seen commercial/industrial amps use both methods of measuring HV. It 
really boils down to a personal choice and component availability. In 
some cases I would also use a seperate string

Carl
KM1H


--- Original Message ----- 
From: "John Lyles" <jtml at losalamos.com>
To: <amps at contesting.com>
Sent: Thursday, December 18, 2008 7:47 PM
Subject: [Amps] metering HV on PAs


> Unless I am very lazy and cheap, I usually put a separate divider in 
> for metering, or a series meter multiplier resistance. You can get 1 
> to 5 Meg skinny but long wirewound HV resistors from various sources, 
> I usually go to the surplus store in town for mine. They can be 0.5 or 
> 1%, sometimes as high as 2% tolerence, and don't drift much as they 
> are high enough as to not be dissipating much power, not like a 
> bleeder whose purpose IS to load the supply a bit, and drain the caps 
> when it is shut off. But using 2 Watt carbon comp resistors is not 
> great, unless you put a lot of them in series. The newer metal oxide 
> and film resistors appear to be excellent.
> 73
> John
> K5PRO
>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>