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.
>
>
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