[AMPS] The Emtron DX2 amp: A 50ohm 50 Watt resistor in B+?

km1h @ juno.com km1h@juno.com
Fri, 17 Oct 1997 09:30:48 EDT

On Thu, 16 Oct 1997 22:00:14 -0700 Chris Victor <cvictor@hooked.net>
>I question the resoning on a high value such as the 50ohm 50 Watt
>resistor in their amp. Seems a little off to me.
>Chris WA6SUY

Used as a full power absorber until the AC mains fuse or whatever blows.
The 4CX1600B is a  fragile tetrode tube with a 100 milliwatt grid and a
20W screen rating. It needs this level of protection. 
In addition you dont want to lose HV to the anode in the case of a simple
flashover. An open resistor would be a problem for the screen circuit. 
>From the Svetlana spec sheet :  "......its value must be 25 Ohms or
more. The resistor should be capable of withstanding the high surge
current caused by the arc, and should not be used as a fuse."  
A 3-500Z, 4-1000A, etc are a lot more forgiving and a smaller value and
wattage usually suffices. 

73   Carl   KM1H
>                 The EMTRON DX-2 has a very sophisticated tube
>protection circuitry, designed to protect against excessive plate
>current, screen grid current, screen grid voltage, bias voltage,
>overdrive, SWR, etc. The tube is also protected from excessive
>temperature by continuously monitoring the airflow temperature. In 
>of any fault, the amplifier is automatically cut off.
>A 50 ohm, 50 watt resistor in the B+ circuit further protects the tube
>and the power supply from a possible internal arc of the tube.
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