[Drake] Drake L4B/8877 Retrofit

[w2cqm@juno.com]

It appears that the Yahoo site I was planning to use in order to share
the details of the retrofit is not going to work for me. I put the
annotations in plain text (below) If you need the  the deck and  power
supply digitals, I'll send them the "old fashioned way" 73's Ron W2CQM/3


Drake L4B/8877 Retrofit 

Part I

	Work has begun in earnest preparing the Drake L4B for its rejuvenation
and  reintroduction into the new century. My  prologue, appearing  on the
Reflector a while back,  announcing the initial phase of the project also
suggested most strenuously  to the Drake Reflector constituency  that the
(anticipated)  bad mouthing,  and those espousing my alleged guilt of 
heresy need not respond.  I�ve been through that gauntlet as a result of
the previous  two  projects dealing with a similar themes. Although I�d
like  to believe it,  I�m not at all convinced that the admonition to
refrain from the bad mouthing   held sway with the zealots. That group
consistently espouses the absolute need to maintain the status quo of 
Drake equipment and nothing will keep them from venting.   Basically, my
feeble request was only rhetoric and offered no tangible consequences if
one elected  to ignore  me and  send along verbal barbs and epiteths. 
Quite surprisingly, the anticipated negative responses and over-reactive,
often foul email posting, never materialized. Not a single comment that I
received  could be construed  as somehow  impacting  on someone�s root
canal nerve to some degree that would engender a response! Amazing!   On
this go around, there were the usual positive comments and even several
Drake owners who volunteered to handle the adverse feedback in the event
the situation arose where I would be in need of assistance in responding.
Very thoughtful of them and much appreciated! One interesting comment was
received  from a gentleman who confessed that he was in that initial
group of �rock throwers�. In the interim period, he had apparently 
re-evaluated his position and offered  sincere apologies for his
unsolicited, out of hand, and thoughtless remarks.  To my mind, it was a
most sincere  and humbling gesture and one that few individuals would 
ever admit to. We chatted, became friends, and  readily accepted each
other�s perspective. That bit of  levity aside, let�s move on with the
more pressing details of this project.   

	I had stated categorically,  that I probably would never undertake a
similar project based primarily on the amount of work involved in getting
the last amplifier up and running. However, in hindsight the project was
indeed psychologically uplifting . I realized subsequently that  many of
the tasks undertaken that made it labor intensive could be eliminated
with some simple modifications to the process. I guess there�s something
to the adage that we   �grow up to soon and smart too late�. 
Additionally, higher levels of  output  could be easily  achieved as
result of some  power supply redesign including the choice of a higher
output  plate transformer. The last project netted 1800 watts output.
That�s  formidable and respectable in any format. However the yarning for
squeezing out  an additional  400 watts was more than sufficiently
motivating.  Notwithstanding the circa 1975 Drake L4B design as it
related to  the early FCC restrictions as to power output, I decided 
almost immediately on another attempt to approach  new heights in L4B 
performance with a relatively simple �supercharging�  process. However,
what continued to offer almost insurmountable difficulties was  the
inability to locate clean L4B�s without power supplies. It�s simply
impossible to achieve high power levels with the stock supply. 
Understandably, the vast majority of radio amateurs  are reluctant to
give up a fully operational Drake.   That was frustrating and caused me
to work the project backwards with the building of the power supply
first. The rationale was that I could always use a big gun supply even
though the Drake L4B might never forever remain elusive.  Here�s  one of
those time savers I spoke about. The last time around, I built the power
supply enclosure myself. It required the work of a metal smith and worked
out to be time consuming and  very expensive. On this occasion,  I took a
more pragmatic  approach and tried out the idea at the Timonium, Maryland
ham fest. I would look for a vintage piece of gear in a suitable
enclosure that could  easily be  reconfigured  to suit my size
requirements. Why reinvent the wheel! There was an abundance of empty
steel cabinets but generally they were too large and for the most part
unsuitable. Fortunately,  I located  a circa 1959  Hewlett Packard 
frequency generator lying amongst several other pieces of dated test
gear. When I inquired about price from the bedraggled vendor, I was
subject to a litany of superlatives about the nature of  boat anchor
gear. Utilizing a universally understood gesture,  I held up my hand,
palm out, to signify that he need not waste any more breath. I explained
that all I wanted was the cabinet. As it turned out, it was just what I
needed. It was louvered, sufficiently large to house the Hipersil, and
made of aluminum for easy cutting. $5.00 did the trick and off I went to
the car subjecting myself to the possibility of a hernia  from the
weight. Most of the innards were junked even though I marveled at the
mastery of the  machining of pulleys and pistons  utilized to generate
stable signals. After  hours of disassembly, I  ended up with a bushel
full of hardware, knobs, tube sockets and all kinds of precision
resistors  that were added to my junk box.  In it�s original form, the
style and design  of the  cabinet resembled an animal carrier with a
handle at the top. In the original HP design, the chassis was mounted
vertically on the rear panel and the entire unit could be slipped out of
the enclosure.  For my purposes, I stood the unit on end with the chassis
now sitting horizontally as the base and measured the height I needed to
clear the transformer. I cut off about 8-10� of cabinet height, a
corresponding length  off the four interior framework supports  moved the
strap to what now became the top. That completed,  I was ready to go. All
I needed was a plate for the bottom on the chassis.  Since I�ve gotten
the 4000VDC @ 2 amp rectifier board, complete with filter caps, bleeders,
and diode modules down to 6x8�, I really didn�t need too much additional 
room. A couple of primary contactors, a 10 second mechanical delay start
relay, a mini computer fan  and two meters  completed the line up of
parts. 220VAC was wired directly to the power supply and dedicated solely
to that part of the project. A 115vac control voltage is brought down
from the deck to activate the solid state 180 second  delay timer on
start up. After the delay, voltage is passed on to the contactors, step
start relay and then to the plate transformer. A half power switch 
position was built into the  supply circuitry as well as an additional
switch control to bump the primary voltage up a tad adding an additional
200 VDC.  Take a look at the digitals to see what resulted. 

Preparing the RF Deck

The work began with the usual stripping out of those extraneous Drake
components. Tubes, chimneys, and tube sockets were removed. Out came the
ALC board, front panel ALC switch, HV and  parasitic choke assembly, and
fan. A great deal of work was eliminated when I decided not to use the
OEM Drake filament transformer. Although the 5vac rating  is OK for the
upgraded tube, 30 amp capacity is a bit too high and results in
insufficient voltage  draw down when using the 8877. Since tube life is
diminished  exponentially with filament over voltage, I purchased the
exact rated  transformer and obviated the need for a small rear panel
mounted  Variac controlling the input voltage. Didn�t need the pin outs
either.  Lots of work eliminated in this step alone with no compromise in
performance. A brand new  115vac line was brought into the deck and wired
to the terminal strip. A fuse was added to the line. One half of the
front panel on/off switch controls the on/off function. Since this Drake
came without a power supply, I really didn�t know what exactly was
working with the unit. That led to an interesting problem.  I rewired 
the amber front panel light to glow on start. No problem there.  I
replaced the  front panel push/pull ALC switch with a rotary 2P2T mini
switch designed to control both the amplifier standby (interrupting the
relay line) and to power up the red lamp signifying that the amp is in
the circuit. Tested out the new wiring and discovered that there was no
red light! I figured I did something wrong. Checked and checked but no
luck. There were no wiring errors.  Decided to run a 115vac  hot lead
directly to the lamp terminal strip. No light!  Unbeknownst to me,  the
lamp apparently  had been smoked in its previous life.  What a bummer!
Everything up to that point had been perfect with the amp so I assumed I
was at fault. Now what?   There are no replacements available  for this
unit at  any place for any price. I anticipated a crisis of epic
proportions since I was intent on keeping the exterior of the  Drake OEM
in all aspects.   In desperation, I lopped off, guillotine style, the
back end of the lamp assembly, removed the two wires, the  charred  neon
and resistor but leaving the bezel and red lens intact. With a little bit
of grinding with a Dremel,  I force fitted, from the rear,  a Radio
Shack� 110vac red panel lamp  into the open end of the Drake assembly.
What I initially considered a  disaster of biblical proportions was
averted with a bit of expediency; and off  I went once more on my merry
way.    To block off the two 3-500 socket holes I fashioned  a piece of
aluminum (left over from the Hewlett Package cabinet cut down) and fitted
the 8877 air system socket to the chassis  utilizing the blocked opening
closest  to the deck�s front panel.  I made certain that the socket was
orientated in such a manner to ensure that  the existing wires from the
bifilar choke  would reach the filament  socket pins without any
modifications. Made that error the first time around.  A custom wound
1x6� porcelain HV plate choke was mounted horizontally  from the chassis
behind the front panel  and positioned  with clearances to prevent HV arc
over and the need to keep anode wiring  to a minimum. I wind these units
with #20gauge enameled wire to handle the anticipated high current. Other
incidental mods included the installation of a standard RCA jack in place
of the two pin relay control plug and the addition of a small transformer
powered  26VDC power supply for the vacuum  and bias control relay. As of
this writing, this is about as far as I�ve gotten. The installation of
several additional accessory items  will be addressed in the next
episode.  

PS: since this was written, the Millen  socket has been repositioned on
the rear panel and the HV lines installed with  all parasitics.
Everything on the upper deck is about completed.