Jay,

I have used CW ID from the U3S extensively with never a problem.

I understand your comments about the shaped waveform and have
already suspected that as an issue. I am not sure what happens at
the end of the waveform using the transceiver in USB mode driven by
audio or the phasing exciter. Based on circumstantial evidence I
suspect those are also shaped or terminate in some way the amp
cannot handle.

The bottom line is I was trying to use the amp in ways you never
intended and it wasn't working.

As a matter of curiosity it would be very interesting to investigate
and find the real cause but I must leave that to those with the
proper test equipment. If the amp could be protected from the drive
conditions which cause this issue I would resume using it. It is
more efficient than my other alternative.

73,
Paul




On 2/26/19 6:32 AM, [email protected] wrote:
> Paul
> 
> Have you run cw from the U3S?
> 
> I have never run cw from a transceiver through the amplifier ...
> instead I always attach a continuous source of RF (GPS referenced
> HP3325A for example) to the amplifier input and use a keyer to
> key the amplifier. There has never been a problem in thousands of
> hours of operation.
> 
> CW from a transceiver is not the same ... it's an amplitude
> varying signal when you consider the rise and fall times of the
> shaped waveform. Rise and fall times of 5 milliseconds used to be
> the 'standard' ...  which is an eternity at 137 or 500 kHz. The
> amplifier, as designed, is not expecting an amplitude varying
> waveform at it's input.
> 
> Jay W1VD
> 
> p.s. in addition to looking at the sound card output for clues,
> I'd also look at the output of the transceiver as well
> 
> 
> ----- Original Message ----- From: N1BUG <[email protected]> 
> Reply-To: <[email protected]> To:
> <[email protected]> Sent: 2/26/2019 6:05:15 AM 
> Subject: Re: LF: Class D current spikes 
> ________________________________________________________________________________
>
>  Jay,
> 
> I was using an HF transceiver in CW mode through a down
> converter.
> 
> Other FETs were lost at end of envelope while running JT9 with
> the transceiver in USB being fed audio from a sound card. The
> latest was with audio from a different sound card into the new
> phasing exciter.
> 
> I have never lost a FET while running with the U3S.
> 
> 73, Paul
> 
> 
> On 2/25/19 8:57 PM, [email protected] wrote:
>> Paul
>> 
>> Was this with a continuous frequency source at the input
>> (HP3325A maybe?) and using a keyer plugged into the amplifier
>> key jack?
>> 
>> Jay
>> 
>> 
>> 
>> 
>> 
>> ----- Original Message ----- From: N1BUG <[email protected]> 
>> Reply-To: <[email protected]> To: 
>> <[email protected]> Sent: 2/25/2019 7:50:17 PM 
>> Subject: Re: LF: Class D current spikes 
>> ________________________________________________________________________________
>>
>>
>> 
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, [email protected] 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" 
>>> <[email protected]> To: "N1BUG" 
>>> <[email protected]> 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.