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Author Topic: Running a DX-60 at low power output  (Read 886 times)
K8CIT
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Posts: 31




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« on: March 19, 2019, 12:23:47 PM »

I would like to use a DX-60 to drive an Elecraft KPA-500 amplifier.  The amp does not require much drive to reach full power output.  I find that if I leave the loading at minimum and just dip the final the plate current at dip is 80 ma.  This gives about the right power output to drive the amp.  My question is....what grid drive should I use for these conditions?
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G3RZP
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« Reply #1 on: March 19, 2019, 02:44:23 PM »

If you reduce the loading, the screen grid current goes up and you could well exceed the screen dissipation. Better is to make a suitable attenuator....
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K5WLR
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« Reply #2 on: March 19, 2019, 03:05:18 PM »

The screen current is tunable and adjustable; just keep it at the setting suggested in the manual.
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G3RZP
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« Reply #3 on: March 19, 2019, 03:52:39 PM »

Tuneable with what? Loading control?

With tetrodes, light, loading leads to high screen current......If there is a clamp tube or fixed bias, the best answer is to back off the grid drive.
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K5WLR
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« Reply #4 on: March 19, 2019, 04:09:20 PM »

The DX-60B has a Drive Tune control and a Drive Level control. When you finish tuning up the final at the reduced output level, you go back and check that the Drive Tune is still set for maximum and then readjust the Drive Level control for the 2.5 mA setting as recommended in the owner's manual.

I own one of these and this is how it is done.  Smiley

Hope you find this info useful!

Will Rogers
K5WLR
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K8CIT
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« Reply #5 on: March 19, 2019, 05:01:30 PM »

I should mention that this is for AM mode.  I did a few mods to the modulator and have a carrier control that I adjust for 100 watts carrier output on the amp.  5 watts into the amp gives 100 out.  Does this clarify?
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K5WLR
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« Reply #6 on: March 20, 2019, 05:46:24 AM »

What does the driver level show when running 5 watts? Just curious....
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WA5VGO
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« Reply #7 on: March 20, 2019, 07:16:26 AM »

Reducing the grid drive will cause downward modulation. Reducing the loading will cause excessive screen dissipation. Use an attenuator.
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G3RZP
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« Reply #8 on: March 20, 2019, 09:51:05 AM »

Isn't the DX60 a series gate screen modulator? If so, it might be possible to reduce the screen voltage to reduce power while being careful not to over dissipate the grid.
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K8CIT
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« Reply #9 on: March 20, 2019, 05:20:14 PM »

WLR not sure what you mean by driver level....
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VE3WGO
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« Reply #10 on: March 20, 2019, 05:43:44 PM »

I'm guessing here, but K5WLR probably means what setting of the "Drive Level" knob (second from the left along the bottom row) results in 5 Watts output?

Load the output properly, and adjust the Drive Level to as low as you need.  If that does not reduce the output low enough, use a series attenuator between the DX-60 and the Amp (as WA5VGO mentioned).

73, Ed
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