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

Ian White, G3SEK G3SEK@ifwtech.demon.co.uk
Fri, 17 Oct 1997 09:49:22 +0100

Chris Victor wrote:
>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
>                 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 case
>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.

For tubes up to about 1500W dissipation, Eimac recommend a resistor that
will limit the absolute maximum surge current to 40A. For a 2kV supply,
50 ohms is spot-on. 

The 50W rating is partly for power dissipation, and partly to make sure
the resistor is physically big (long) enough to avoid internal arcing if
2kV suddenly appears across it.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)

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