[Amps] Drake L4B to 6 Meters Help

[Jim Thomson]

From: gudguyham at aol.com 
Sent: Monday, December 12, 2016 2:56 PM
To: jim.thom at telus.net 
Subject: Re: [Amps] Drake L4B to 6 Meters Help

Too much operating bias drastically lowers the idle current and you need more drive power to make more suds.  The Drake L4B when properly converted to 6 meters should easily do 1300 watts pep on SSB with 100 watts of drive and the idle current on SSB at about 200ma.  Idling way down kills output power and increase drive for the same power output.  All considering with accurate metering and into a dummy load. 


##  Agreed.     But drakes oem  zero bias resulted in  220-230 ma of idle current = 600 watts on idle = blast furnace.   With 10 x 1N5408 diodes in there,  idle drops to just 100 ma... =  260 watts. 

Sure, drive requirements will rise slightly, since you now require more drive voltage to overcome the  7.2 vdc of bias.   Another 10-15 watts of drive.  No big issue, provided you have plenty of drive.   If the 100w xcvr will barely put out 100 watts is one thing.  But if a 200w xcvr is used, its just dialed in  to required drive level. 

##  If the  oem grid + chokes are removed, and grid pins bonded directly to chassis  with cu strap, the drive power requirements  will typ decrease by  20-25 watts..... at least on the 160-10m bands.  
So it comes out a wash.   Drive requirements increase cuz of  7.2 vdc of bias V..... but then decrease  IF grid pins are bonded to chassis. 

##  with 200 watts of dive available, and also adjustable bias V, both on the fly, it’s a non issue.   But if drive is limited, and bias V increased,  po will drop slightly.   PO comes back up when grids are bonded to chassis..
so its still a non issue..in most cases.  100-150-180 ma of idle is fine..... but 220-230 ma is nuts.   And if B+ is  3300-3700,  high idle current will result in  excess high idle power.

##  The typ 200w xcvr, when run at 100w, is very clean IMD.   Not so for 100w xcvrs...like the K3, with its lousy  -29 db pep  IMD3.  

Jim  VE7RF