[AMRadio] Ranger... good news, bad news


Gary Schafer garyschafer at comcast.net
Sun Nov 5 21:03:04 EST 2006


John,

Are you peaking the output circuit on the SB200 after you reduce the drive?
If you are just using carrier out of it to drive the grid of the next amp
you should peak everything to get maximum efficiency. Efficiency should be
near 60% even at the low power level if you retune the plate circuit.

73
Gary  K4FMX
> 
> 	I have used the SB200 on AM and it does OK but I would not want to
> do it for a long time.  Those tubes get real hot.  I use the SB200 as a
> driver for my big rig.  The input to the SB200 is about 5 - 10 watts and
> the
> output of the SB200 is about 50 - 70 watts carrier this drives the grid of
> my big class C plate modulated final.  But even using the SB200 to put out
> 50 - 70 watts it get real hot and the tube show some color.  I think the
> best thing I can do to increase the efficiency of the SB200 at low power,
> is
> to reduce the plate voltage to about 1500 instead of 2500.  I added a
> switch
> to the front panel of mine to increase the bias voltage making it harder
> to
> drive.  I thought that this would decrease the conduction angle enough to
> reduce the heat but the trouble is that the plate is still not reaching
> saturation at the low power level so I figure that if I reduce the plate
> supply voltage and increase the drive then I can come closer to the non
> linear class C service for continuous CW and the efficiency will surly
> increase.  The idea is to use the rice box rig at low power so it will
> last
> a long time and have the SB200 to make up the slack. But I want it to last
> a
> long time as well.  BJ and I like the flexibility of this type of
> operation.
> That is to be able to flip some switches and use the SB200 as linier on
> SSB
> as it was intended and then flip the switches back so as to lower the
> output
> but raise the efficiency for continuous carrier operation as required by
> the
> big class C final.  We have been operating it linearly with the 2500 volts
> supply and reducing the drive from the rice box carrier source but it has
> always bothered me that it is so inefficient and those tubes show color.
> As
> I recall the PS in the SB200 is a voltage double type circuit perhaps a
> little circuit change up with some HV switches might be in order here?
> Any Ideas on this?
> 
> 
> John, WA5BXO





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