[Lowfer] W1VD amp help

[Chris Wilson]

Hello Paul

I had no luck with the W1VD X2 when I used it with part of a W1VD pre
amp from another of his circuits. I think the issue was my not
matching the input or output of the preamp section right. I also found
my TS-590 did not start and stop WSPR TX from the 0dBm output socket
cleanly, and the FET's didn't like that one little bit.

All you need to do is set the X2 option in your U3S menus, and take
the drive DIRECT from the Si chip output. I also found I NEEDED to add
0.1uF ceramic caps DIRECT to ground on all the VCC pins on the W1VD
driver board. Otherwise at QRO levels I got RF influencing the gate
and hence drain waveforms. Here are typical gate and drain waveforms
run on 50V (I see about 159V peaks on the drains at 55V) If the drain
waveforms are noisy and ragged look to antenna matching issues or
coronas.

If you drive it with a thin co-ax from the U3S Si output pad on the Si
board (I go to an SMA socket on the back of the U3S enclosure) and
miss out the 51 Ohm to ground resistor on the input of the 74F74 you
will effectively be doing exactly what I do, so we can directly
compare. One thing I did notice re your amp build is the gate driver
twisted pairs are a lot longer than mine. I have the driver board
right by the FET's so the gate leads are maybe 1.25 inches long.
The diodes and 10 Ohm resistors are right on the FET leads, down low.
If  you blow a FET it often takes out a diode or two and sometimes the
resistor,  so  I just replace them on any blown FET (which is now very
rare).

Below  is  the  circuit  as I now use it, I built my own driver boards
sans the safety and keying extras.

http://www.chriswilson.tv/amp-less-surplus-controls.jpg

http://www.chriswilson.tv/gate-and-and-drain-U3S.jpg

Sunday, April 8, 2018


> It seems I'm in over my head again. I'm having difficulty getting my
> newly built W1VD kW 137 amp to run correctly. I think the problem
> may be with my driver board.

> Question 1:
> Could anyone with a known good W1VD kW deck send me a scope plot of
> your gate waveform please?


> Question 2:
> Using the driver circuit exactly as shown here

> http://w1vd.com/137-500-KWRev3.0.pdf

> what have you successfully driven it with? Please specify sine or
> square wave and drive level.



> Here are the problems I'm having:

> Using the configuration shown in the pdf schematic above my amp will
> not drive with either sine or square wave input at any level up to
> +23 dBm from a HP 3325B at X2 frequency (275 kHz).

> When I add this X2 multiplier

> http://w1vd.com/X2LinearClassDinterface2.pdf

> between the 3325B and the amp, it works. Sort of. I changed the
> 3325B to 137.5 kHz of course. I get about 65W with 13V on the drains
> and 250W at 25V. But, something goes into oscillation when RF drive
> is removed! Not the FETs. It's either the driver board or the
> multiplier or the combination of the two. I can see it oscillating
> when I probe the input to the driver board. Oscillation starts only
> after RF drive has been present and then removed. Neither the
> multiplier nor the driver board show evidence of oscillation when
> not connected to each other.

> I may have additional issues at high power but I think I should get
> the driver working correctly before proceeding further.

> 73,
> Paul N1BUG





-- 
Best regards,
 Chris    2E0ILY                        mailto:chris at chriswilson.tv