[Amps] Drake L4B

[zl1aih at ihug.co.nz]

Hi Jim,
If you want to keep the L4B pristine/unmodified and used only on festival days then 
you're OK, but keep your fingers crossed.

If you ever wanted to use it as a contest amp then put the power supply in a dry 
storage area, and build a real power supply that will do justice to the amp - 
minimum 2.5kV under load.   Ours is 2.5kV @ 1A, but you use what you have in the 
junk box.
   
Do whatever is required to take care of relay sequencing and if you can tolerate the 
noise, sit two muffin fans over the 3-500s.   Rubber bumpers and 'Blue-Tac' will 
stop the fans from wandering around the cabinet top.    The original blower was 
never going to keep those tubes cool under more than SSB ragchew conditions.

One caveat - the unfiltered blower plus 2 muffin fans can pull a lot of dust and 
rubbish into the amp - depends on it's environment.
Also, check the condition of the filament pin contacts and measure the filament 
voltage at the pins (not the socket connectors) - do this before connecting the HV 
from your new power supply.<G>

Ours is used only for Multi-Single contesting, and is cleaned before each major 
contest.   The original 3-500s are still delivering full output.
YMMV.

Good luck and 73,
Ken ZL1AIH (ZM1A in CW contests) 
  

>I recently picked up a nice L4B with power supply, SN 1934.  The tube
marking was pretty faded, but are Eimac 3-500Zs, date code 7115.  the
amp and PS are real clean and look physically pretty good.  I have 
removed the two filter cap/ diodes boards from the PS.  I think the 
Sprauge caps are original.  They all reformed nicely and are showing
less that 1 ma current at 450 volts.  I will likely change out the 
diodes for some 3A 1KV diodes and button things up.  Are there any
other 
caveats, or issues that I should be looking for before I put this
thing 
on line.  General comments on the L4B are welcomed.  I will be using
the 
amp with my Drake B line twins.>