The AM Forum

  Buying a Heathkit is like buying a box of Cracker Jack, you never know what you will find inside.

  Bought a SB-303 the other day. The usual spiel, estate sale stuff, don't know if it works and etc. Turns out it probably was too close to a lightning strike; 80 meter antenna coil fried and RF amp transistor fried. Also, the usual broken slugs in the coils, broken wires and some things that, if built this way, it never would have worked. Only the SSB filter installed (ever).

  Anyway, can anyone reccomend an available substitute for the RCA 40673 used in the RF amp? Would anyone have a 40673?

Thanks,
           Bill KA8WTK

NTE222, 3SK40, 3SK41, 3SK45, 3SK48, 3N200
http://www.danssmallpartsandkits.net/
I believe all the "3SK's" are no longer made but vendors may still have stock.

3N200s will also work & 3N187. I have an SB303 that came with a bad FET in the kit. Took a while to find the problem. DC voltage at the source is a good first check.
3N141 will work but it isn't a protected gate.

I may have some 3N204's hanging around from a VHF receiver I designed back in the late 70's.  If they will work for you I will see if I can locate them.  I am not sure if they have protected gates or not.  Frank, you probably know.
Joe, W3GMS

One place to start for specs and substitutions, is here:
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/

and, since Google is your friend, you can generally search "device number" specifications and also get your answer.

I think the 3N204 is a better device. I think it is protected. I have 3 of them in the IF strip of a HB RX.

Bill,
I just returned from the GMS parts building and sure enough, 3N204's are in stock!  Let me know if you want a few and I will mail them out to you. 
Regards,
Joe, W3GMS

Motorola changed their 3N200 series part numbers to start with 'MFE'. MFE201 = 3N201, MFE204 = 3N204 etc. MOT stopped making them a while back but there are still some around.   

Hi Bill,
   I have a couple of 40673's I can send you if you decide to stick with the original part#

Ed

What a generous group!

I had a PM right after the post and am getting one from there. I hope it is the only bad one in the radio. We have been going stage by stage finding where the unit fails. The RF amp appears to be the last glitch, but you never know!

Again, thanks for the offers and the information. If I find myself still in need after I put this one in, I will PM one of you.

Thanks Again to All Who Replied,
                      Bill

wear an ESD strap when you handle FETs and make sure the soldering iron tip is grounded, they are easy to zap.