[Lowfer] W1VD amp help

[N1BUG]

Hi Chris,

Thanks for the information!

My gate waveform is somewhat similar. I had wondered about the
rounding at the leading edge of positive peaks (mine looks very
similar to yours in that respect) and ringing, if that's the correct
term, at the leading edge of the negative peaks. The latter concerns
me a bit as mine seem to show quite a bit more of it than yours.
Maybe that is related to the longer twisted pairs or some other
circuit layout detail. However I can't rule out anomalies in the
scope as mine is old, tired, and needing calibration. Not much I can
do about that.

Honestly I haven't looked at the drain waveform as it's clear my
driver circuit is not healthy. I figure to try sorting that first
because it may very well affect everything downstream.

I may try your drive method as a means of verifying the amp works in
simplified form. Unfortunately it's not a long term solution as I'm
not content to use the U3S as my only exciter. I also need to be
able to use my FT-2000 and home made converter. This cannot easily
provide 2Fo drive nor a proper square wave. Even if it could, most
software for digital modes is incapable of 2X tone spacing. It's
entirely likely, if not probable, that I may find some reason for
wanting to use the 3325B as a driver for some mode or other. Hence
it is my intent to always run Fo drive into the W1VD doubler on the
amp input (and presumably the full, unmodified amp driver circuit).
The trick is getting all that to work. In the  absence of any
troubleshooting information I feel lost as usual. I'm an analog guy.
I've never used a logic IC in my life til now!

I saw some additional problems during a brief test at 38V / 550+
watts out. This may be related to bypassing as with what you found.

Paul



On 04/07/2018 09:11 PM, Chris Wilson wrote:
> 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