Re: LF: WSPR-15 last night

[N1BUG <paul@n1bug.com>]

Hello Chris,

OK after this first time (switching to the 32N20 type) I will try
changing just the bad ones. I'm sure there are better FETs these
days but I will let someone with more technical knowledge sort out
which ones might work in this PA. I have enough self induced
problems already... ;-)

73,
Paul



On 11/20/18 12:56 PM, Chris Wilson wrote:
> 
> 
> Hello N1BUG, I don't change any that remain functional and haven't had
> an issue. I do use a very cheap Ebay IR temp gun to check all run
> similar temperatures and find that a good way to see if one is working
> overly hard. I just checked, it's the 32N20 that I have always used. I
> think it's the voltage rating rather than current that's a bit
> marginal. and there are probably much better FET's with lower gate
> capacitance around nowadays for similar cost, but I am loathe to
> fiddle until it becomes necessary :) I was talked into buying a used
> Metcal RF soldering station at a rally some years back. Best thing I
> have ever bought electronics wise. With a high temp tip it will
> de-solder and re-solder the drain wire from the copper strip so fast
> everything else does not melt. Until you try one it sounds too good to
> be true, but I am now 100% converted. With a small tip it is great for
> surface mount tiny stuff, too.
> 
> 
> Tuesday, November 20, 2018, 3:32:50 PM, you wrote:
> 
>> Hello Chris,
> 
>> I would be interested in the collective wisdom of the wise ones in
>> this group regarding replacement of FETs. Given they've all surely
>> had a strain when one or more blew, is it really wise to just
>> replace the ones that check bad? I'm leaning toward replacing all
>> four whenever one or more is dead. Am I being too paranoid?
> 
>> I really wish we could socket the FETs.  When I am in there this
>> time I may see if I can find a not too messy / not too destructive
>> way to mount those copper strips the FET drain leads solder to so
>> they can't move around. When replacing FETs I find it oddly
>> aggravating holding that metal strip in place. Invariably the heavy
>> lead from the transformer then comes unsoldered from it and I have
>> to try to put that back without any drain leads or the snubber cap
>> coming unsoldered. It'd be nice if that copper strip were solidly
>> mounted and the transformer lead bolted to it (I think)...
> 
>> I can still get FETs in the big package if I go 32N20 instead of 34N20.
> 
>> 73,
>> Paul