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From: N1BUG <paul@n1bug.com>
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Message-ID: <92784b07-a799-fb4e-9080-e1e8bb167b75@n1bug.com>
Date: Mon, 25 Feb 2019 19:50:17 -0500
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In-Reply-To: <1UTEEgOcyQ.DAejAuRZtn9@optiplex980-pc>
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Subject: Re: LF: Class D current spikes
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Reply-To: rsgb_lf_group@blacksheep.org

Jay,

Good idea, but it isn't just the sound card. I can guarantee one or
more destroyed FETs after sending two or three characters of CW
where computer and sound card are not involved at all. I can also
confirm that with CW the FETs are still blowing at the end of RF
envelope. I can hear the fuse when it opens. I tried some very slow
CW to confirm exactly when it was happening.

73,
Paul


On 2/25/19 7:30 PM, jrusgrove@comcast.net wrote:
> Chris
> 
> Thanks for the waveforms ... very informative. Sure looks like
> something is triggering the input of the amplifier and thus
> causing the problem.
> 
> Since the problem doesn't exist with U3S's (which generates the
> various modes internally) driving the amplifier (either directly
> or through a frequency doubler) one has to wonder what the
> difference is between the U3S and the other exciter setups that
> cause the problem. The fact that the U3S / amplifier combination
> works correctly would argue that the 'problem' is likely not the
> amplifier.
> 
> The one thing that the non U3S setups have in common is that the
> modes are generated by software / computer / sound card. Think
> the first step in tracking down the problem would be to see if
> there are any unexpected outputs from the soundcard that are
> causing the problem. When you get a chance maybe you can capture
> waveforms of the sound card output up to and after the end of a
> transmission.
> 
> Assume that you have disabled all 'computer sounds' on the
> machines that are supplying audio for the various modes?
> 
> Jay W1VD
> 
> 
> 
> 
> 
> ----- Original Message ----- From: "Chris Wilson"
> <dead.fets@gmail.com> To: "N1BUG" <rsgb_lf_group@blacksheep.org> 
> Sent: Monday, February 25, 2019 5:02 PM Subject: Re: LF: Class D
> current spikes
> 
> 
>> 
>> 
>> Hello  Paul. everyone
>> 
>> A  series  of  overlapping  scope  captures  at end of WSPR 
>> sequence  with  expensive  high  voltage  /  current  Wolfspeed
>> FET's that usually survived, into the antenna and into a 10kW
>> dummy load, taken after  the choke and also at the drains of
>> the W1VD amp. Driver TS-590 /  W1VD  doubler,  and W1VD amp (
>> end part of another circuit). U3S does not show anything like
>> this oscillating end to a TX sequence.:
>> 
>> http://www.chriswilson.tv/wolfspeed-choke-and-drain-50v-smps-antenna.zip
>>
>>
>> 
http://www.chriswilson.tv/wolfspeed-choke-and-drain-50v-smps-dummy-load.zip
>> 
>> Green trace drain, yellow after the choke.
>> 
>> 
>> 
>> Monday, February 25, 2019, 4:34:05 PM, you wrote:
>> 
>>> Chris, LF,
>> 
>>> Yes, although I run mine differently. I use the full output
>>> of the U3S into a doubler. I have run WSPR, JT9, and DFCW
>>> from the U3S without having any problems. I have also
>>> extensively used CW ID with the U3S and amp without problems.
>>> Yet both other exciters blow FETs at the instant RF stops.
>> 
>>> Chris, I know you are busy but if you get a chance I would
>>> like to see those scope captures. I thought I had it figured
>>> out that this is a voltage mode amp and should be seeing
>>> current spikes, but maybe I still have that wrong! If they
>>> are voltage spikes that may be easier to control.
>> 
>>> One thing I would like to learn more about is why do the
>>> drivers leave one phase high for a longer period than a half
>>> cycle when RF stops. What causes this? Is this only with
>>> specific FET drivers or are all of them prone to this?
>> 
>>> 73, Paul
>> 
>> 
>>> On 2/25/19 11:13 AM, Eric NO3M wrote:
>>>> Chris, et.al.
>>>> 
>>>> N1BUG relayed the same information regarding the U3S and
>>>> class-D amp behavior, so your observation is not a one
>>>> off...
>>>> 
>>>> 
>>>> 
>>>>> 
>>>>> I have a series of scope captures from my W1VD amp
>>>>> showing huge voltage spikes on the FET drains at the end
>>>>> of WSPR and especially OPERA TX sequences. I suspected
>>>>> inductance was the cause. In fact I try not use OPERA at
>>>>> high power as i am pretty sure to kill a FET after a few
>>>>> sessions... Oddly (although I hope msomeone more 
>>>>> knowlegeable has the answer), using WSPR from my U3S
>>>>> direct from CLK0 of  th  Si535a  or  whatever it is never
>>>>> causes these spikes...  Or at least they are well
>>>>> contained.