[Amps] HV Resistor Source

[Carl]

Ameritron/MFJ sells a Globar they use for a glitch in their "senior" amps. 
Overpriced and uneeded IMO at those power levels. A plasma isnt going to 
even get started before the fuse blows anyway...this aint a 250KW 
application!

Carl
KM1H


----- Original Message ----- 
From: "John Lyles" <jtml at losalamos.com>
To: <amps at contesting.com>
Sent: Wednesday, April 17, 2013 4:24 PM
Subject: [Amps] HV Resistor Source


> The "industry standard" for such a resistor is a pulse rated R like a 
> Kanthal Globar. The company has changed names a lot recently, so search 
> for them. These are carborundum bulk resistors, non inductive. You can 
> live with inductance of a WW, of course, but in a dead short, you might 
> find your resistor flashing over with plasma. Then it isn't such a good 
> resistor. Globar isn't cheap, but they are excellent in this application, 
> as well as for dummy loads. You have to study their literature, type AS 
> and SP material. One is better for continuous dissipation and the other is 
> best for very high peak voltages but low dissipation. They make them with 
> clip in connectors or wires.
>
> 73
> John
> K5PRO
>
>
>> Message: 8
>> Date: Wed, 17 Apr 2013 00:58:47 -0500
>> From: donroden at hiwaay.net
>> To: Amps at contesting.com
>> Subject: Re: [Amps] HV resistor source
>> Message-ID: <20130417005847.27844mn5ynlr261j at webmail.hiwaay.net>
>> Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes";
>> format="flowed"
>>
>> Quoting Jim Garland <4cx250b at miamioh.edu>:
>>
>> > That's going to be quite a resistor, inasmuch as 4KV across a 30 ohm
>> > resistor amounts to a half million watts of dissipation!  A 4KV pulse 
>> > 50uS
>> > wide, once per second, would dissipate 25W.
>> > 73,
>> > Jim W8ZR
>>
>>
>> The resistor isn't to ground..... it's in series with the tube(s) that
>> may draw 1 amp intermittently ... therefore 1 amp squared through 30
>> ohms is 30 watts.
>>
>> If the tube draws more amps ... a short or a bad load... maybe a two
>> amp spike... that is 120 watts which will hopefully burn out the
>> resistor
>> ( acting like a fuse ) before the transformer or diode stack goes up in 
>> smoke.
>>
>> Don W4DNR
>>
>> ***
>
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