[amsat-bb] Re: Icom AG-25 schematic

[Greg Beat]

Bob -

Here are the documents, web links, and answers from QRZ Q&A.
http://forums.qrz.com/showthread.php?290978-3SK121-FT-726R-70cm-module-Q01

AMSAT-BB -- December 23, 2001 (Joe Leikhim, K4SAT)
http://www.amsat.org/amsat/archive/amsat-bb/200112/msg00609.html

Toshiba 3SK121 -- TOSHIBA TRANSISTOR Dual-Gate, UHF, 10V, Idss>20mA, Up<4V 
Datasheet (largely in Japanese).
http://www.datasheetcatalog.org/data.../499109_DS.pdf

The Icom mast-mounted pre-amplifiers (AG-25, AG-35) use the dual gate 3SK121
Dual Gate FET.
The 2 schematics/manuals for the Icom AG-25 and AG-35 units are at QRZ page.
 
You will see Internet recommendations for the 3SK121 replacement on AMSAT
and 
VHF/UHF DX discussion boards based on this usage by Icom.
These two distributors indicated they had inventory of this Toshiba
Dual-Gate FET.
 
XS Micro 
http://www.xsmicro.com/rfq.php?pn=3S...&ref=octoparts

and Express Electronics (UK)
http://www.express-elect.com/

I have seen one Eastern Asia exporter (eBay Seller id: my_mkchan) based in
Hong Kong 
offer a variety of Yaesu parts, including some hard to find (no longer mfg.)
transistors.
 
I have seen the European CF-739 or BF981 listed as a suitable substitute.
 When you substitute check Noise Figures and Gain for your application.
 
BEWARE of Counterfeit (Fake) Semiconductor Parts from Asia .....
http://sound.westhost.com/counterfeit.htm

===
w9gb

 
----- Original Message ----
> From: Bob- W7LRD <w7lrd at comcast.net>
> To: amsat-bb at amsat.org
> Sent: Wed, January 9, 2013 4:05:35 PM
> Subject: [amsat-bb] here's a good one!
> 
> Getting ready for a AO-7A pass, started keying the transmitter, I 
>noticed the computer monitor was blinking very nicely in time with the 
>cw, also the az and el indicators on the G5500 control unit were dancing
around in tune with the cw.
>In fact they danced in tune even with the power off. Tipped over 
>satellite tower, got out ohm meter, direct open through the 2M Icom 
>AG-25 preamp. Jumped around the now removed preamp and we're back in 
>business. Question...The relay contacts seem to be suspect. Should I 
>get parts and repair the AG-25 or get a better preamp, as I am going to 
>scratch some EME efforts off my bucket list. If you have a better 2M preamp
"laying " around let me know.
>
> as always
> 73 Bob W7LRD