[Amps] some tips about select and use FU-728F ---- Xmas cookie

[Hsu]

The Chinese FU-728F first intruduce in 2005 or 2006  by myself in amps 
reflector. Before that year , as far as know,NEVER non-chinese had ever use 
and know it .
  In past years ,some homebrewers and amplifier manufacturer( EMTRON) begain 
to use it.But many people did not  know it at all.
The FU-728F develop in end of 1960s or early 1970s for Chinese TYPE 70/76 
1600W ISB/SSB transmitter, this equipment widely use in
land forces , navy and air force in 1970s to 1990s in China.FU-728F design 
baseed on FU-100F( similar  4CX1000A) by Chinese, so without any
tube can replace it direct. it can regards as longer( taller) FU-100F , 
longer anode and cathode, so it with bigger power rating.
   There are three version of FU-728F, please view the picture here: 
http://www.zmdz.com/bbs/incomefiles/201112/2113423610426.JPG, and 
http://www.zmdz.com/bbs/incomefiles/201112/2113425923319.JPG  right: is the 
oldest version, it was built before 1987 even end of 1970s,
this version usually   have  shorter tube life, the oxide  is  easy flake 
away from cathode if over drive a bit,
this led to  the cathode and grid shorted;the left( mark ¡°J¡±), it is a 
newer  and  better  version, it built in the end of 1980s   to  1990s; the 
middle , it is
best version and    made  in 1990S to now, this version's quality better 
than Russian GU-84  and near Eimac's.The  left and middle seems same , but 
look
at fin carefully, the left  with  dense fin , if you still not
see it clearly, please look here 
http://www.zmdz.com/bbs/incomefiles/201112/2113431253493.JPG. te top  is te 
best  version of FU-728F .
  These are three version of FU-728F and their   difference.

About the manufacturer of FU-728F, There is only a manufacturer in China 
today, it located in Jiangxi Province.You can  see the left tube  what mark 
¡°J¡±
with difference logo,red star like US air force¡¯s logo, it is BOE Groupe¡¯s 
logo , although BOE groupe havd ever made FU-728F ,but duo to  the quality 
problem,only
few tube were produced. Most of BOE¡¯s tube actualy OEM by jiangxi Planet.
  How to use this tube? first, it must use shunt screen regulator, because 
this tube often have larger negative screen current, if you use
serial regulator  like ARRL Handbook ¡°Suny Vale¡±/Saint Petersburg 
Kilowatt-Plus¡±, you will damage  the screen power supply.
If you use a pair  tube , you must use  same version tube, because 
difference fin will led one of tubes over heat.
  about the socket, FU-728F¡¯s sockets can not fit 4CX1000A¡¯s but 4CX1000A¡¯s socket can fit FU-728F.Why? I do not know.I know  US  force rife's
caliber is 5.56mm, Chinese is 5.8mm, maybe it is the  eastern trick.LoL! You 
can modify its socket easily, jut replace centering pin,
so te socket can fit both.In past few tyears, I have supply some modify 
sockets to EMTRON.
   Finally, the price, the newer version NOS tube usually quote  $250 to 
$300, but old version is cheap, from $50 to $220 .Please remember, no free 
lunch in the world.
I do not recomded old version, very easy to damage. The factory new tube 
quote $450 orso. Now, My amplifer use factory new  only.
     Merry Xmas and Happy year!

   73!Hsu