Yeasu FT101 #1 deaf as a stone.

[N3DRB The Derb]

Plugged in the front end board from #2 and it improved a bit but still way down, because that board got blitzed too.  Believe the front end active device got blown away. This is the third time this has happened. Is there another front end thats a bit more rugged that could be plugged in?

forgot it's a 3SK40M FET - maybe there a better replacement now afta 25 years?

[WBear2GCR]

back to back diodes across the input (gate) or before the resistors etc that are in front of the part? That would be diodes across the input, each facing in the opposite direction... the idea is that they don't conduct until the ~0.6v threshold is reached... after that they do conduct very hard.

You might look to see if that is already present (usually is) and if those diodes were toasted. If they were, then that is the clue.
You might do well to put some hefty silicon power diodes in the hole to better handle the excess current/voltage that killed the ones that presumably were there and killed. I'd put high voltage rated diodes in.

If they make a hyper low voltage "transzorb" that might work, but I rather doubt that exists or is necessary.

Btw, there nothing "hefty" about a FET gate. No part will be any better.


Just replace the FET, put a socket in the hole and forget about worrying about it getting zapped. Buy a spare or two, and you should be good forever...

               _-_-bear

[Ed-VA3ES]

Be aware that on some FT-101's, the crystal filters deteriorate.  The internal foam that  cushions the internal crystal lattice   turns to mush and  stops the filters from working. The trick is to open up the filter case, clean out the foam mush with acetone, trichlorothene, methyl chloride, etc,  and re-seal the case.

The symptoms of this is poor sensitivity.

[N3DRB The Derb]

yeh, they are socketed already. I'll just order a bunch of them. This one does not have that lamp fuse in it.

whoops - did a few minutes of looking and the 3N211 from motorola is better has built in diode protection and better noise figure, etc. etc.
Guess I'll snag some of them. Drop in replacement for the 3sk40 part wherever it's used.

John,
I remember having used the 3N211 as a replacement in the front end
of the YAESU FT-101 transceivers. If I recall the transceiver had much
better sensitivity after they were installed and they were one of the
easiest
upgrades that you could do for an FT-101 of any vintage. The 3N211
also had diode protection across the FET junctions where the 3SK40
as originally used by Yaesu in the front end did not. I may be wrong,
but
if I remember correctly the diodes prevent them from blowing out
from static electricity on the antenna or something like that.
I know that doesn't answer your question and I don't know if that
tells you anything you didn't already know about the 3N211
you did not already know.
I just thought I would pass on what I remembered about the Yaesu
FT-101 in regards to the 3N211
Regards
Carol
W4CLM

[Ed KB1HVS]

There is one in the pb-1180 (box). Another known failure point. Ive replaced them with the Motorola fet

[N3DRB The Derb]

thanks ed I'll go in and get that one too. I'm looking for a good price on them now.

[N3DRB The Derb]

found a sub with the diode protection on ebay for a good price Ed. MFE201 drop in replacement.

my skyhook blew down during the big storm yesterday. 

Gonna put the W7FG antenna up in it's place.