Ricebox as VFO

Discussion in 'Technical' started by KX5JT, Jan 21, 2015.

  1. KX5JT

    KX5JT Guest

    So my TS-570 can dial down to 5 watts... is this too much for my Viking II VFO input?
     
  2. W5HRO

    W5HRO Administrator

    The 6AQ5 buffer is putting less than 5W into the 6146 grids so yes. I think the amount of drive there is around 1W + or - a little.

    What you can do is buy one of those 100W 50-ohm attenuation pads and connect it between the transceiver and VFO input connector. Just calculate the db of attenuation you need to get it down to 1 watt with say maybe 10 watts of input or more. It would also make the input a perfect 50-ohms for the transceiver starting at DC on up. The 570 would always think it's on dummy load. I'd get a 100W model as a safety factor to handle the transceivers full power and because you might want to use it for something else someday, but you are going to want to be able to dial the power input to the Viking II's VFO SO-239 connector down to under 1W. The 100W pads are a little pricey though, but I have seen some for as low as $200 to $300 before. Just search around the web for the best price.

    Example:

    One note, the tuned circuits on the 6AU6 and the 6AQ5 may want to tune up on a harmonic so you may need to tweak those circuits a bit so they tune up on the direct fundamental frequencies and don't try to multiply them instead.
     

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