 Collins 30L-1 Recovery |
I had acquired a Collins 30L1 from a friend that rescued
the amplifier from a pile of junk at a scrap yard in the next state. The
yard owner had purchased it from one of the East Coast Military Bases
as "scrap metal". The unit had been "de-milled" by
being bashed repeatedly with a hammer or similar weapon. The case took
a lot of hits,the meter movement was smashed and the case bent in. An
interior inspection revealed smashed tubes, broken driver coils and bent
plates on the final tuning capacitor. But over all not an extreme basket
case. A project that I was sure I could waste many adult hours trying
to get the thing running again.
A shot of the side view showing removal of the meter and the beginning of the process of removing the main HV caps board.
Closer view showing the HV caps and the bleeder resistors
. I had checked the HV caps with a outboard power supply and found one
marginal device and replaced it. I put off doing the meter movement to
build up my nerve for the later disassembly and repair.
Bottom view of the 30L1 to the right, showing the diode
board, and the equalizing network of capacitors and resistors
On most of my HV power supply projects that I am not
trying to retain the original components I sub the"K2AW Hi-Voltage
modules. His ad is in QST. I have never had a failure of the modules and
they are very easy to mount. Left is a shot of a HV bridge using four(4)
K2AW modules on another project, not the 30L1.
During the "de-mill process the weapons hit several of the driver coils.
Since the coil bases were ceramic, I really had to dig
into into the junk box to find replacement ceramic forms.
Replacing
the coils involves more than just removing the wire and putting it on
a new form. I wanted the replacement driver coils to have the same "tuning
range" as the previous coils. . . this would help tuning on the repaired
bands. I dipped "working coils"to get a good feel for the response
of a good coil and noted the approximate tuning range. It was very difficult
removing the old coils, lots a disassembly of the main chassis.
Once I got the new coils wound I replaced
them an dipped and added or removed turns, positioning the wire on the
form to get the proper tuning bandwidth
Remember this tool? Its a Heathkit nut holder great for those tight places and putting assemblies back together.
Now comes the fun, testing the amplifier. The piece of red plastic tubing made from an old test probe is used to over ride one of the safety grounds or interlocks of the HV supply which is activated any time the covers are removed.
One of my favorite pieces of test equipment is a home brew isolation station consisting of a large isolation transformer, AC amp meter system and a large variac. This system makes it easy for trouble shooting large power supplies as you can bring the line voltage up slowly and keep an eye on the amp meter, if the amp meter starts to peg out then sit back and enjoy the show, you will soon know which component is bad.
Another good safety precaution while "testing"
is to cover the component area with a piece of lexan plastic, this prevents
the shrapnel from leaving the chassis area and becoming embedded in parts
of your anatomy, always wear safety glasses or stand in another room.
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The tubes were replaced and looks like the filaments are at least working. The picture may look strange because the 811 finals in the 30L1 are mounted horizontally. If you don't like the 811's mounted sideways causing "filament sag" then simply put the amplifier on its side.
The
30L1 ready for action. The meter was repaired after careful surgery.
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