RL Drake L4-B Amplifier All in One, Soft-Start, Soft-Key, & Bias Module Kit

Product Description

The ES4L4-B is a combination soft-start/soft-key/bias board for the L4-B amplifier.  This all-in-one board limits inrush current during amplifier start-up by placing a small resistive load in series with the AC mains. 

The load resistor is switched out of the circuit by a relay approximately 2.5 seconds after power-on.  It also features a opto-isolated soft-key circuit that reduces the voltage on the keying line to 12 VDC at less than 10 mA current that is also interlocked with the soft-start. 

The kit also utilizes a string of 10 1N5408 diodes and a 100KΩ resistor to provide DC cutoff bias and user-adjustable idle current biasing. 

There is also a ready light output on the board for those who wish to use it.  The unit mounts on the underside of the RF deck using existing holes in the chassis; no extra holes or modifications to the chassis are required.  The board is assembled and comes with all necessary mounting hardware, miscellaneous parts and wiring.  The Instruction manual is included.

Comments from Jim (VE7RF)  sum up the benefits to installing ES4 L4B

  Paul's  ES4L4B superb board is an eloquent solution to a myriad of issues.  All solved in one shot.   And you can't  key the amp, till the  2.5 sec delay has finished.   The  B+  and fils are both step started, and bias is adjustable.   The opto-isolator key  line buffer is unique, in that it then eliminates the requirement for the spst  mech relay in the yaesu ( and other)  xcvr's. The mech relay in the FT-1000D  adds another  15 msecs  to the mix.  IE: Trip vox,  15 msecs for relay in yaseu to close.. then another  15 msecs  for  3PDT TR relay in L4B  to operate.  Meanwhile,   TR  relay in amp hotswitches.   The spst mech relay in the yaesu  1000MP-MKV  is  just 5 msecs.  Same deal...an  unnesessary  5 msecs added to the mix..and same hotswitching.

With the keying buffer, the  SS circuit in either yaesu can be  used to interface to the ES4L4B keying buffer.   That just eliminated  5/15 msecs of delay.   Plus the spst mech relay can be shut off in either yaesu....so  the xcvr is totally quiet.  ( the yaesu's use pin diode  TR  setup). 

 I used an  opto-isolator as an interface.   The yaesu  MK-V has an adjustable  0-30 msec  delay for the key line.... ( to give the amp a head start).... but that only works for  CW, since it  buffer's the CW).   Doesn't  work for  SSB.  

 Paul's  board does what all my external ..and internal stuff does....  all on one board on bottom side of L4PS  supply.   Paul's  board also eliminates the  fubar +130 vdc  drake used to bias the amp off on RX....while still  retaining  the oem  ALC  function.  ( no more burned up center contact of 3pdt tr relay).   His board also turns the +26 vdc oem Drake  half  wave rectifier...into a  +26 vdc  FWB rectifier.  That doubles the +26vdc  current capacity.   Ok,  now it's all set up for a  vac TR  relay  mod, if desired.

 So no, Drake  didn't  quite get it  right back in 1963.   You won't find any amps built these  days without  step start, none. 

Jim   VE7RF