The Commander Lives....
By Bill Morton W4ASE
As many
of you know I always seem to be looking for an inside project in the late Fall and Winter time. Once Spring arrives, I have plenty
of outdoor projects to keep me busy. I am not sure when this desire started in my life, however, each year I seem to try find a project
from all of my interests: computer, work or Ham radio related. In thinking about this article, I reviewed some of my earlier Ham radio
projects - early tune up pecker design and production, repeaters, repeater automation, repeater auto patches, rebuilding of Motorola
and GE radios I got as scrap from the Railroad in Augusta, GA., Meter Builder 1, Station Pro 2, Remote station, Automation of Remote
station and on and on. In fact, the other day I ran across one winter's project from the early 70’s. This picture is of a Motorola
HT-220 with a touchpad. One of a kind. I build it from 3 junked HT-220's that I bought as scrap from the Railroad. It has a 5 watt
kit, 5 channels, and a custom touchpad. I charged up the battery and it still works just fine, but it is crystal bound and nothing
like today's modern HT's, but it is something that I created from a pile of junk.
Well, this year is no different and I was looking
for a project when one presented itself to me. Jack Ray W4JBR came on the air one night and we talked about the flood he suffered
3 or 4 years ago. He had some equipment in a rack that was under water for a period of time and he had never moved any of it. I knew
he had a Commander HF-2500 amp that was in the flood. I contacted Jack and we discussed if he wanted to sell his amp "as is where
is." After some serious negotiating we came to a price that was fair to both of us. I knew I was buying a pig in a poke. There was
no telling what damage the water had done. I knew of course the tubes would be good and I could sell them and get a portion of my
money back, but past that it was a crap shoot at best. I went out to Jack's house and picked up the amp. When I turned it on its side,
3 - 4 year old water ran out. Having taken plenty of VHF radios to the car wash when rebuilding them, this looked like the only course
of action for this amp. Once I looked inside I knew I had a real job on my hands. I took it home, opened it up and started removing
parts that did not need additional water damage. Out came the meters, transformer and a few other things. Then I made a quick trip
to the wand car wash to wash out as much mud as I could. I brought it home and set it outside to dry in the sun. I took the transformer
and placed it in a small oven at low heat for 2 days to make sure it was dry. Now it was time for serious disassembly. It became clear
that there was plenty of corrosion in every ground connection and a number of aluminum parts had a white corrosion on them in particular
the variable caps looked rough. Here are the steps I went through for the Frame Off Restoration:
Step 1 Car Wash Cleaning
After
removing all of the parts that a new bath would hurt I found a good wand car wash and got most of the mud off
and out of the amp –
then I let everything dry for a while. The use of a car wash may sound harsh but I learned to do this back when I repaired and retuned
Motorola radios for 2m - always good to start with a clean unit.
Step 2 Disassembly
While Commander used stainless steel
hardware for the most part - they used plain steel lock washers that had all rusted. It be-came clear that this would a frame off
restoration for this amp, with as much new hardware as possible. The amp was completely taken apart. Along the way over 50 pictures
were taken of the take down to insure proper reassembly. This number of pictures proved to be one short of the number needed - more
on this later.
Step 3 Transformer
The transformer needed to be tested. After the drying out, I used a Variac and a small value
fuse to put a little AC into the Transformer. I got the correct voltages for the input I had applied, so things looked promising.
I move the voltage up to 110vac and got all voltages at 50%. Now time for 220vac. All voltages looked fine. I decided to go back to
110v and then put a small load on all the secondaries. I left it to "cook" for several days. I finished off the testing with full
loads on the secondary with 220vac input on the primary. The transformer performed as it should - it had survived the flood, which
made the restoration both possible and financially feasible. If the transformer had been bad I would have parted the amp out.
Step
4 Rebuilds and additional cleaning
Part of the Fan case had to be rebuild due to rust - a little sheet metal work, spot welding and
some paint brought
the case back to life - the motor and squirrel cage were fine once cleaned and re-lubed
Variable caps were left
in a 65 degree Centigrade ultrasonic cleaner for two days to remove all the corrosion – they
came out fine - not like new but clean
and corrosion free - however, now they needed to be re-lubed.
The Squirrel cage from the fan was cleaned and the motor disassembled
and lubed.
All hardware was cleaned in the Ultrasonic cleaner – much of it was replaced as it was in very rough shape.
Corrosion was
the worst thing I had to watch for. They did use Stainless steel for the most part but plain steel for
lock washers and they were
all rusted – you can see the rust rings in some of the pictures around the screw holes
on the top—corrosion and the effect it had
on ground connections proved to be a very big problem.
All silver parts (except tubes) dipped in Tarnaway and then washed and cleaned
again in the Ultrasonic cleaner.
This process made all the silver look new.
The toroid coils were clean/soaked with Oxyclean to remove
the mud stain. The cloth around the toroid was white again.
Repaired the solid state TRIAC on/off switched for the 220V. This was
actually the best use of modern technology in
the amp – a very cool circuit. They used solid state relays for control of the 220v
primary.
The Meters were disassembled, cleaned, oiled and checked out - they seemed to survive the flood as well after rebuilding
and testing.
Step 5 Upgrades
Teflon wire and COAX now used throughout the amp – there was some Teflon wire but now it all is.
Replaced
TR relay with a vacuum relay from Gigavac... The original TR relay was too badly corroded. There is a
“Ham Special” accommodation
price from Gigavac which made replacement reasonable
Replaced the control relay with a sealed unit—it was badly pitted from corrosion
All RCA connectors upgraded to gold plated with Teflon inserts
RF in and out SO239’s upgraded to Teflon inserts with silver plate
Front panel LED’s replaced with modern ones
Meter incandescent lights replaced with bright white LED strings - much nicer look to
the meters
All hardware that showed any signs of corrosion was replaced. This was harder than it might sound as some of the
screws
were special. I was forced to use some of the old hardware in non-critical areas
New front panel Power and Operate switches, which
Jack had, were installed.
Clean Clean clean - every time I though I had gotten all the mud I found more.
p 6 Left to do
In a project
of this size there are always other things to do – but truly there are only a couple of projects left to do -
either rewind the plate
choke or install a new one – the one in it has been repaired along the way and was missing a few turns where it popped. Size is the
issue. It would be easy to just pop in an MFJ coil that they use in the ALS-1500
($20) and it would be fine but it would be a bit
tight on room. The good news is that it is very easy to get to and only
require about 11 screws to be removed to replace it. I wanted
to test the amp with the original plate choke first to see
how it does then think about replacing it. The other project is that the
Plate meter is reading low compared to my Fluke
high voltage probe – which I know to be accurate – the problem with this one is that
the voltage divider network for
the meter is deep inside the RF deck and would take hours to get to now. So this one may just have
to be overlooked and left as it is. It is reading low about 10%....but I guess on reflection that is as close as a Bird gets with
a hair dryer.
tep 7 Testing
Because each sub assembly was removed from the amp and cleaned, it made sense to test each one as I went
about the process. So I set up power supplies and a testing facility to test each part of the amp’s control and power supply circuits.
Some like the RF deck would not be able to be tested till final assembly, which proved to be a small problem.
ep 8 Final Check out,
Make RF and problem solving
Whenever, I have done serious work on an amp in the past I always start the rebuilt amp back up in the
easiest band for it to work on - 80 meters and then move to 40 meters, not wanting to try any of the higher bands till 80 was absolutely
stable. This amp was no different. When I first brought this amp up it tuned very funny on 80 meters. I could get 1500 watts out of
it but things were just real squirrely and it seemed like a strain. After several days of thinking I had a bad tube in the Commander
HF-2500 and then possibly a power supply problem having to do with Bias and a host of other possible problems, worrying Milton for
suggestions I might not have thought of to test and on and on I had just about resigned myself to the fact that this was just the
way this amp worked. So I decided to make my full band settings chart 160-10 and assume this was just the way this amplifier will
work. I started off on 160. It tuned up great - tuned as you would expect an amp to work and could get easily 2kw+ out (even with
the very big voltage drop for 220v that I have with the 100ft extension cord running from my power panel to the shop) with none of
the load problems I had seen before on 80 so I recorded the settings. Then back to 80 with renewed spirit – still the same very strange
load control action. Ok on to 40 – I could not get much if any RF out – I was once again depressed – on to 20 not expecting much and
she fired right up 2K+ out with tune and load working as you would expect. 20 – 10 were all working as I would expect - none of the
squirrely action of the load control. Hmm now what does 80 and 40 have in common. Well there is a Toroid transformer attached to the
tank coil with taps for 40 and 80 off the toroid. Naw surely (and don’t call me Shirley) I could not have reversed the two wire taps
that come from the toroid – they run together in two separate Teflon sleeves from the toroid to the band switch along the same route
– they were de-soldered in de¬construction. So I sat down with the schematic and all my pictures to see if the two taps MAY be reversed.
Well with almost 100 (50 pre and 50 post rebuild) pictures I had, no one picture clearly showed the two tap wires and their positions
coming from that toroid. But after comparing three different photos and looking at the toroid (which now is deep inside the amp and
is was not easy to see) I came to the conclusion that I had made a mistake in the rewire. I had found the problem. So many connections,
parts and wires with this rebuild that a mistake was certainly possible – that is my story and I am sticking to it. I set about to
reverse and re-soldered the two taps – which was not as easy as it would have been had I done the soldering correctly when the amp
was in the rebuild stage. 80 and 40 now tune correctly and none of the strange load action is seen on either band. Grid current looks
as expected. I can get about 2K out on both bands with my very poor 100 ft. 14 gauge extension cord for my 220 source. Can’t wait
to see what it will do on a real solid 220v source. I have one more small problem in the timing circuit for the tube count down at
start up – but I have run across a Mod for it and I think the addition of a 5mf cap will solve my problem. But for all practical purposes
the amp is done and working as it should.
Outcome and Overview
The Commander is a well-constructed AMP – but technology is not its
strong suit - Solid construction, time proven circuits and quality parts are. I have seen homebrew amps with more electronic technology.
The use of two 3CX800A7 tubes which is a problem now as they are very expensive if replacement becomes necessary. But I think it will
be a solid amp for me now that it has had its “Frame Off Restoration” – time will tell. My understanding (and I am not sure about
this) is this was the first time that a voltage doubler circuit in the high voltage power supply was used in a commercial amp. They
enjoyed the circuit so much that they also use a doubler to take a 5 vac winding to make the control 12vdc for the amp control. Once
I found my rewiring mistake in the RF tank circuuit, tuning and operation were all normal and it operated as you would expect. I have
enjoyed this project and now spring is here. Next year on to a new project for the Winter. Oh yes, that does mean I have an extra
amp that is being rebuilt now. Not a frame off—but serious updating of the B&W PT-2500 with 2 3-500z tubes.
The Commander Lives.....
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