The kit is available for 100.00 plus shipping from The Heathkit Shop. The website offers
shipping information and parts availability. WB8VGE can be contacted by email and his
address is available there.

Now...remember above all YOU COULD BE KILLED! Yes, become a silent key!
So if you think you have what it takes to do this, let us begin...

If you are reading this article You have one of the best HF power amps ever to be released on the
Amateur radio market.
Drake radio gear was always respected for quality and design. There are many of these amps
still in use today, but some of them are dieing for one reason or another. The possibility does exist
that a large percentage of these problems may be related to poor power supply capacitors.
Here are a few tests.

Turn on the L4-B and leave the room for a while.
(1) If, when you return, there is an odor of hard boiled eggs in the room, the caps are bad.
(2) If the caps show cracks on the top and they bulge out or weep at the wire lead, they must be
replaced.
(3) If the top of the PS-4 cabinet feels very warm and (hot) on the end sides, without the amp keyed up,
your caps are bad.
(4) Your HI-Voltage drops while in tune up mode, the caps must be replaced.
(5) On the air reports of harsh audio with the L4-B in the circuit, generally speaks of poor filtering,
or bad caps. (There are other symptoms as well, but if the caps are the original, well...)
You should order your kit now...before you hurt the amp or worse, destroy the power transformer.

Let us start the repair.
First, remove all power from the supply. Disconnect the cable to the L4-B and place the supply on a
stable bench top or table. Do not build the PCB at this time. There are a few items that we should look
at first.
Here is what you get from Mike Bryce at The
Heathkit Shop. The package you receive includes
all parts required including a very heavy PC board. The
board is solid and will withstand the heat required to build
and support all components in this power supply upgrade.
Remember you are replacing 2 OEM boards with a new one (1).
All components are quality and the manual is well
written. Mike, however, does not own an L4-B
so he must include an addendum to the PS-4
upgrade. The information here is a slight spin on
that addendum. There are a few steps I cover here
that were not covered in the addendum.
Please discharge the HV capicitors first !!
Open up the PS cabinet first, The PS-4 is held together by several screws on the top and on the bottom.
panel. Also, there are 4 located along each side panel. You will be required remove these in a step later,
but for now, remove only the screws that hold the covers to the PS-4 chassis.

There are 2 circuit breakers on the serial number side of the chassis. Two screws below the AC line cord
grommet must be removed, but the grommet will hold the top cover in place. You may remove the bottom
plate and disconnect the power cord from the terminal strip or you may simply remove the grommet and
slide the case cover back to yield the components. You must remove the bottom and the top completely
for this upgrade.
You will now remove the
four screws on each side.
This will render the OEM
diode boards loose and
ready to remove.
On the right side you will
see the ceramic insulator
with the .82 resistor that
feeds the bleeder. This
insulator will be in the
way if you try to remove
the diode stack.
Note: Cut the wires that
feed the stack as close to
the PCB as possible.
You will cut the power
transformer secondary
output (2 red) leads.
Cut these as close to the
PCB as possible. You
will cut the small white
(shown here) and a
small red lead that will
be discarded. The red
lead passes through the
chassis to connect the
two boards together.
On the left hand diode
stack board you will
cut the B+ main feed
off the board. Now
remove the insulator
by carefully removing
the machine screws,
one on top and one
on the bottom of the
chassis. There remains
a possibility the you
will break this part if
you force the diode
stack out of the
chassis. If your PS-4
has the small mica
insulating washers on
the bleeder resistors,
they could be broken
if you force the board
out of the chassis. Be
careful.
On the left hand side
the secondary leads
are connected. Be
sure you cut these two
red wires as close to
the stack as possible.
Also remove the large
red wire that feeds the
bleeders. This wire
runs over the chassis
from left to right. Do
not cut the black/white
wire shown in the
picture.
Note the small screws
along the edge of the
diode stack boards.
There are 3 on top
and 3 on the bottom.
You must remove these screws and retain the 4 mounting brackets. You will choose 2 (two) of these for
mounting the new PCB into the chassis. Now that you  have the boards out, clean up your work and
take a small break. Begin by having a cup of coffee and read the instruction manual.
Ok break time is over...
In this picture please note the 3
holes located on each side of the
PCB. (located at 'A', 'L' and 'D'
on the board). These holes are
for mounting 2 of the 4 brackets
you removed from the diode stack
boards. In some cases these holes
do not line up with OEM brackets.
Before you begin installing parts
onto the board, make sure the
mounting brackets fit properly.
In my case they did not, and I had
to drill the center hole larger to
allow all holes to line up. You do
not want to leave the center hole
unattended. Do not drill the PCB!
Drill the bracket center hole large
enough to line up and insert a
number 6 by 3/8 machine screw
and nut to mount the bracket to
the PCB. Check both sides and
remove the brackets and set them
aside till the PCB is populated with all the parts. The above image shows the board after step 1 is complete.
Be sure to stand the resistors (R1 - R8) up off the PCB as shown. In the second step you will insert the
diodes and the equalization
resistors (150K). Note that
your finished board should
look like this. All diodes on
the inside row face toward
you and the outside row
faces away from you. Be
sure that the solder has flow
through the PCB where the
diodes and resistors mount.
Note the pad in the center
of the board marked as
"R11PIN6", this is a very
important solder pad. I
will discuss this step later
on in this text.
Now double check your
work and lay the board
aside for a minute.
Open up the capacitor
parts bags (2). You
will find 8 (eight) very
high grade computer level electrolytic capacitors. They will be marked with a  NEGATIVE band only. So
obviously the opposite terminal is positive. To insure the caps are inserted properly, mark the caps with a
red paint pen as shown here.Marking these
caps will insure you of proper installation
into the board. The PCB markings can be
a bit confusing, not by fault, but simply
because there is no '+' marking on the
HV caps. The PS-4  is a voltage doubling
circuit. You do not want to install a capacitor
in the wrong configuration. In the image you,
see I also marked the diode band just so
you could compare your completed work
here...
The white arrows show the diode band
directions. If your boards looks like
this, you are ready to run a voltage test.
This can be done by attaching a small
12 VAC transformer (6 or 18 will do)
to the lands marked 'red' and 'red1'.
(See the image below) If you, after
power has been applied, have 25
VOLTS DC across the output
(2500 VDC and R11PIN6).you
have completed the PCB successfully.

Take another break!!
If there is anything to be said about the L-4B, it must be with regard to Drakes quality and design.
The L4-B is nothing new and it certainly is a standard when it comes to amplifiers. However the choice
of components and the quality throughout makes this a superior BOAT ANCHOR. Unlike the "state
of the art" today, this amplifier will kick ass for years to come; especially after you have made this
upgrade.
We will complete it soon enough, but first I want to tell you about mine. I purchased it used from a
local. He had 2 other amps for sale and was thinning out the herd. I chose the Drake because I had
Drake equipment in the past and always trusted it for quality and longevity. The L-4B is no different
than any other Drake equipment, and this comes from a guy who ran a Drake 2B along side a 
Tri-X-500 back in the 60's.
Well not to get too long winded, this L4-B, smelled like rotten fish. It was horrible when it was on
and the smell remained in the shack like a bad fluorescent transformer. I searched the Internet for a
solution, thinking it was the transformer that was indeed the biggest problem. Well I was wrong! But
you might be able to relate to this; when the L4-B was on, the power supply was extremely "hot" to
the touch. The sides of the cabinet were hotter than the top. There was a raspy sound to the amplified
signal and the power would fall off if I was long-winded.
So the search on the Internet brought me to "The Heathkit Shop" (The link is above.) This is where I
found my salvation. The PS-4 power supply upgrade by Mike Bryce. After making the upgrade, I
tested the amp and found it was making 2450 VDC in the SSB position. The output was no longer
raspy and CW note sounded great! Best of all was the smell (gone) and the cabinet was almost
too cool when you consider the power supply heat dissapation. I added a fan on the outside of the
cabinet for grinnys and I am having a ball. My L4-B is a dream that I have always wanted, 2 (two)
3-500Z in a dark room at night !!! I won't need the furnace vent anymore...

Ok, in the picture above there is an ORANGE wire that I soldered to the pad at R11PIN6. This wire is about
12 inches long and it will be used in a step later. This is the NEGATIVE side of the output and it must be
wired to a terminal stripe under the main chassis. I added this wire to replace the "small red" wire that you
are told, in the addendum, to retain. I suggest you solder this wire before you attempt to insert the PCB upgrade
into the PS-4 cabinet.
Here is the upgrade board as it
sits inside the PS-4 cabinet on the
left hand side. The wiring tip above
is the same, but the wire in this
view is WHITE. Note the 2500
VDC connection and, if you can
see, the wires from the power
transformer connect to RED and
RED1 on the board. Again, if
your upgrade looks like this, you
right on the money.
Now, mount the board using the
existing hardware and check to
be sure that your transformer and
HI-VOLTAGE leads do not
touch the chassis under the PCB.
Now the white (orange) wire
that you soldered to "R11PIN6"
can be routed on top or under
(as displayed) the upgrade PCB.
I routed mine under the board
and out of a spare hole in the
board and through the grommet
in the chassis floor. This wire is
connected as shown in the
image below.
The WHITE and RED wires
will carry the 3-500Z final tube
high-voltage. There is 2500 VDC
across these two leads!
In better terms, 1 (one) board
replaces 2 (two) very tired old
diode stacks that should be
considered ancient technology.

In the final steps, you will be routing the white (YL's should use pink) wire down to the output cable terminal
strip. Here you attach the wire and cut the small white wire that we showed you in an earlier image. Do not
cut any other wires. You are connecting the white (orange or color of your choice) to the yellow wire on the
strip as shown above. (Note: I chose to use 14 gauge stranded for this connection.)
so there you have it...now on to the final test. If you had no problems with the PCB test using a 12VAC
transformer as explained in this text previously you are ready to break in the caps...
Place the covers on the chassis. Replace the bottom and then the top. Make sure you have the AC power
source cable installed through the grommet properly. Check all your wiring on top before you close off the
cabinet. If you feel that you have completed the upgrade and are satisfied that all the wiring is
correct, complete the following step!
Here is how I test the finished power supply. Note
that I use a Soft Touch power control. But for the
capacitor break-in we use a Variac. Mine is on
220 VAC and it supplies about 225 from the power
Variac. I start at 100 Volts and slowly bring the
AC voltage up to 220. I use 25 volt steps and
take about 1 - 1.5 hours to break in the upgrade.
You can use light bulbs in the primary circuit
but be careful not to unbalance the 220 VAC
input. If you run 110 VAC to your L4-B, you
can use a Variac or single bulb to do the break-
in step. I cannot recommend running your L-4B
at 110 VAC, but...
I can recommend you purchase the kit and do the upgrade. I don't care how good you think your caps
are, I am telling you to do this. It ain't about making money, at 100 bucks, there is not a lot of profit even
if the man is making 25 % markup. I don't know how much profit Mike is making, I can only tell you that
it isn't enough as far as I am concerned. He saved my PS-4 and my L-4B. For that I will be forever
grateful. Enjoy the power supply upgrade and have a blast with that L-4B.