Hello LF'ers,
Saturday, March 25, 2017
Thanks for all the replies on my heating toroid question, as best as
i can tell it's not the core per se that's heating, more the 4 turn
primary winding, made of pure copper, multi strand speaker "figure
of eight" cable of about 2.5 mm core diameter. It never gets over 65
to 70 degrees Celcius, in a warm room and then only on WSPR15. I
have added a small computer processor fan above it and it stays at
ambient then. I think I am worrying needlessly. the amp draws about
20 amps from the PSU. Apart from that I have not had one of my FET
explosions in weeks and it works 100% reliably now.
To W1VD, thanks for the update re PCB's i would like to buy a few
more should you get another batch done, so please bear me in mind.
The cause of my FET failures was either my doubler, or pre-amp, or
more likely my TS-590's peculiar waveforms at the end of a WSPR
transmission. i now drive the amp with a simple Hans Summer QRP Labs
U3S which is PC independent, and shows a clean stop waveform at the
end of WSPR and OPERA TX periods. I could have had excess agin in
the pre amp before the doubler, or oscillation, but as the U3S frees
the TS-590 and PC from TX duties I am happy to just use the U3S for
now, with a TCXO installed. The FET's, on an uncooled medium size
heat sink stay around ambient even after long TX sessions, they got
quite hot when driven by TS-590 at 1mW / pre-amp / frequency doubler
combination. Appreciate all the helpful responses!
> Gluing two together improves heat dissipation and no change in ratio is
> required. So far I have found no requirement to alter primary turns
> either until at least 10 turns are reached.
> On 24/03/2017 19:13, Chris Wilson wrote:
>> Hello LF people,
>>
>> If I have a ferrite toroidal output transformer for a push
>> pull Class D 136kHz amp, that gets warmish after a WSPR15
>> session, what would happen if I wound the same number of
>> primary and secondary turns on two cores stacked together,
>> all else remaining the same? Would it run cooler, but
>> retain its transformation ratio, or would other things
>> occur to make it not that simple? Thanks.
>>
--
Best regards,
Chris mailto:[email protected]
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