LF: Re: [Lowfer] FET change, hmmm

[DAVE PICK <daveyxm@virginmedia.com>]

Paul

Try the Infineon IRFP260MPBF they are fast and reasonably priced. I use Ixys IXFH58N20 but they are expensive... they are the best though!
Can't find any FQA34N20 over here from reputable sources.

Dave G3YXM
> On 30 November 2018 at 12:58 N1BUG <paul@n1bug.com> wrote:
>
>
> Yesterday I replaced FETs in my 2200 meter amplifier. Since the
> FQA34N20 is long discontinued I had no choice but to make a
> substitute. I chose the FQA32N20C because I know of one active
> station using them in the same amplifier with success.
>
> I notice drain ringing is significantly greater with the new FETs,
> but maybe acceptable. I have little choice but to run the amp and
> see how it goes.
>
> I also notice the gate voltage decay takes about twice as long as
> the old FETs. According to the data sheets, turn off fall time on
> the 32N20C is almost twice that of the 34N20. I suppose that is what
> I am seeing. I *guess* this may be related to increased ringing, as
> it appears one side is not fully off as the other begins to switch on.
>
> I would appreciate any comments or suggestions, including
> suggestions for a FET which might leave a longer dead zone at the
> phase transition. I'd think slow to turn on, fast to turn off would
> be nice...
>
> Alternatively, if anyone has a stash of FQA34N20 purchased from a
> well respected vendor (old stock) and would be willing to sell some,
> I may be interested. I've already tried some which originated from a
> Chinese source and am not interested in going down that road again. :-)
>
> 73,
> Paul N1BUG
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