From: "jrusgrove@comcast.net" <jrusgrove@comcast.net>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
References: <942860C848184BA2A0A9103E0EE56DF7@DELL4>
 <1UTEEgOcyQ.DAejAuRZtn9@optiplex980-pc>
 <92784b07-a799-fb4e-9080-e1e8bb167b75@n1bug.com>
 <1UTEEhG1Ft.EdI1dlVbFOZ@optiplex980-pc>
 <3062ef19-bb69-3187-e8db-6a6bf5050739@n1bug.com>
Date: Tue, 26 Feb 2019 06:32:56 -0500
Message-ID: <1UTEFdI23a.FvP0vZytwK@optiplex980-pc>
In-Reply-To: <3062ef19-bb69-3187-e8db-6a6bf5050739@n1bug.com>
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Subject: Re: LF: Class D current spikes
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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 <paul@n1bug.com>
Reply-To: <rsgb_lf_group@blacksheep.org>
To: <rsgb_lf_group@blacksheep.org>
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, jrusgrove@comcast.net 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 <paul@n1bug.com> 
> Reply-To: <rsgb_lf_group@blacksheep.org> To:
> <rsgb_lf_group@blacksheep.org> 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, 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.
> 
>