Hi Chris :-)
I guess that finally found what was wrong with my PA!
The last available FET survived to the test yesterday and the only
thing warming is the dummy load :-)
This morning will stop sending wspr on MF and switch the antenna to LF
performing longer transmissions like a wspr15 and looking if everything
is stable.
Although the Decca style is appealing, this design lasted for several
years.. till a small ceramic variabile cap in the directional coupler
of the LF console decided to arch :-( and started the avalanche: one
dead FET (of course), roasted DC choke (the winding was melt and the
stacked toroids changed the colour fron yellow to white !) and ... last
but not least a d...ned RCA connector on the output transformer. This
one was the reason of quick launch of the brave replaced FET: it was
completely charcoaled but in an hidden position so never detected this
till yesterday when the last brave FET lasted enough to make it to
smoke..
Now the PA is delivering 53 dBm (240W) and the heatsink is barely warm.
So now let start to radiate 200mW on LF ;-)
Cross the fingers...
73 Marco IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 16-apr-2017 13.48
A: <[email protected]>
Ogg: Re: LF: Happy Easter MF LF VLF
Hello Marco,
Sunday, April 16, 2017
A very happy Easter to you too, Marco. From myself and my FET's alive
and switching, and from those in the great recycling bin in the sky! I
hope your FET's survived the evening and live on to bravely go where
no FET has gone before.
I am amazed by pretty much everything Stefan does, I am hope he has
some financial backing, just keeping him in copper wire and toroids
looks like a job fro a wealthy man! Amazing stuff on VLF, simply
amazing.
All the best Marco.
> Best wishes to all the group.
> A special one to Chris and his brave FEts ;-)
> Tonite while the QRP TX is on on MF, a couple of proud FET will
> challenge for the last time on my QRO TX:
> will apply low DC power and then increase sloooooooooowly till the
> standard level monitoring everything.
> If also this last trial will produce smoke instead of RF power will
try
> an H Bridge or half bridge Decca style!
> I'm just concerned how to find place for the inductor.. the box is a
> bit crowded ;-) but with the low required Q probably can do it with
a
> low permability ferrite (I have in the junk an FT240-61 that should
be
> a reasonable compromise).
> By the way, amazed from the picture of the huge stack of toroids
used
> from Stefan for the fine tuning!
> 73 de Marco, IK1HSS
--
Best regards,
Chris mailto:[email protected]
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