Message-ID: <15b7ad07eff.marcocadeddu@tin.it>
Date: Mon, 17 Apr 2017 09:28:56 +0200 (CEST)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: LF: Happy Easter MF LF VLF
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Status: RO

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: dead.fets@gmail.com
Data: 16-apr-2017 13.48
A: <rsgb_lf_group@blacksheep.org>
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:dead_fets@gmail.com