KWM-2 in rough shape

Discussion in '"Boat Anchor" & Classic Equipment' started by KK6IYM, Aug 6, 2017.

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  1. KK6IYM

    KK6IYM Ham Member QRZ Page

    This past weekend, I installed a new relay for K3. I did not use the exact replacement relay because it had not arrived and probably won't for some time. I did use a new Panasonic HL2-H-DC110V which is a 10A, 250VAC, 10 Kohm coil, general purpose relay from Mouser for $13.23. The relay was the right size, but had no mounting hardware. I took the cover off and used a small drill to start a hole at the right spot in the side of the cover. Fortunately such a spot existed that didn't interfere with the action and could hold a machine screw that would then use the original hole through the chassis. Next, I heated the screw and melted the hole from the outside. Then I placed the screw through the hole from the inside, holding it with a pair of needle nose pliers. The plastic case rested on the side of the chassis where I utilized an existing hole and the pliers were holding the screw on the other side of the hole. Then I used my soldering iron to heat the screw. When it was hot enough, I gently pulled it to seat the head into the plastic case slightly. I let it cool and mounted the relay in position with the screw very loose. The wires and capacitors were attached and then the relay fastened fully in place, with a final few connections made at the end.

    It works! And it has been working great while I continue on with the project. I now get about 30 watts out on several bands, less on others. But progress is better than no progress. The rest of the weekend was spent repairing the meter, cleaning the meter switch, and replacing all the meter circuit resistors. I removed, took the works out, tried this or that, and then replaced the meter at least 10 times--maybe more. I lost count after a while. Eventually, I went to the garage and retrieved a meter from another rather decrepit KWM-2. It had its own set of problems.

    These meters are typical of many meters. They have a glass held in by a ring (loose and needed to be cleaned and re-glued), a zero set screw (post broken off the rear which had to be drilled and a small piece of wire inserted with glue to be a new post), a permanent magnet field, a moveable armature on a delicate pivot with coil springs attached, and a brass fork that attaches to one spring and can be shifted to change the zero position of the needle. One problem is the needle, attached to the armature, is on a pivot with sharp points at either end. There is a screw at the front, that can be used to adjust the end play. If it is too loose, there is play and the armature will pull off center and hang up on the field. If it is too tight, it won't swing freely. The big problem arrises when very small bits of steel are introduced into the meter. It only takes a tiny grain of metal to screw things up. These get trapped in between the field and the armature and hang up every time the needle swings. The strong magnet makes removal very difficult or impossible. Never work on a meter with it out of the case in an environment that is not completely free of any small metal fragments. I had these in both meters when I got them and the meter would operate sporadically. I ended up using a strip of paper bout 1/4" wide to slip up in between the armature and the field and clear away the problem fragment. So far it hasn't returned. Another thing to be aware of is that the tension on the spring loaded washer holding the zero adjustment should not be very much-- just enough that it won't move on its own. Otherwise you run the risk of shearing the plastic post on the rear of the front screw head.


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  2. W6ELH

    W6ELH Ham Member QRZ Page

    Still enjoying the "battle reports" Norm. Thanks for sharing! Cheers... Jim W6ELH
  3. KK6IYM

    KK6IYM Ham Member QRZ Page

    Yesterday, I was back at it again. This time, I went through the transmitter signal injection protocol, checking signal voltages needed to start grid current flow at the various stages of the transmitter. This led me to discover an open 1k plate resistor for V5. By open, I mean broken clean in half and hidden against one of the turrets. The radio does work better with plate voltage to V5. I also added the diode to the PA screen feed which has greatly helped the switching between transmit and receive. With those things done, I re-did the alignment, neutralizing, carrier, IF, and loading trimmer adjustments.

    After following the manual procedure, I ended up with 100 watts out on 80 meter, and about 40 watts on all the bands but 20 meters where I get about 10. This led me to play around with the slug for the RF plate. I was able to reach a compromise where I get 80 watts on 40 and 80 meters, 45 watts on the higher bands, and still end up with 10 to 15 watts on 20 meters. It has always been very weak no matter what I have tried to do to increase the performance--even at the loss to other bands. What I do notice is that the RF trimmers are all maxed out capacitance-wise when this compromise state is reached and the RF plate slug does still have a peak point.

    The radio has come a long way from its original state. Now, I need to find out why the 20 meter band is so weak, which hopefully could lead to helping some of the other bands as well.

    KD2ACO likes this.
  4. KK6IYM

    KK6IYM Ham Member QRZ Page

    The Mixer Plate trimmers were all at or near maximum capacitance which made me want to adjust the inductance slug a little at a time so that the 7.0 trimmer would be closer to 1/2 capacitance. The Mixer Plate 14.0 trimmer never did much and the slug had been earlier adjusted to get some output on the 20 meter band. I tested the capacitance of the 14.0 trimmer and it was not changing when I moved from full to minimum so I took it apart. The lower disc had moved off the contacts. After cleaning with denatured alcohol and reassembling the trimmer, it read and operated correctly.

    This led me to try other trimmers. These are easy to test with the cans removed. A capacitance checker is place across the leads and the capacitance is read. Then the trimmer is adjusted slightly up or down and the capacitance is read again. It can then be reset to the original position by checking that the capacitance agrees with the original reading. If the capacitance doesn't change when it is adjusted or if it reads wildly incorrect at various settings, then the trimmer needs to be disassembled and cleaned.

    I found another non-functioning trimmer, this time for the 40 meter band, at the RF Plate.

    The radio now has about 70 to 90 watts on all bands (except 10 meters is lower) and seems to be working as it should. It is very sensitive as a receiver--low noise, good calibration except 10 meters, plenty of gain, and the S meter is responsive. The transmitter gets good grid current for low mic gain settings at Tune on all bands. I am not sure it is worth chasing down a higher RF output. It seems to be in the driver stage. There is a little fading during tune up, but the driver tube tests strong.

    If a person really wants to learn about the KWM-2, then find one from the Peruvian military that dates back to the first year of production (#1048). You will be fully educated by the time it starts to work normally.

    KW4H and WA2FXM like this.
  5. W9GB

    W9GB Ham Member QRZ Page

  6. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    :D Norm, that comment gave me a chuckle -- I'm in pretty much the same boat with an old receiver at the moment. By the time I get it operating normally again I'll be "fully educated" (if I don't go stark raving mad first).

    Anyway -- a note for you -- if you ever need replacements for those Collins trimmer caps, you can find them over at Surplus Sales of Nebraska. I ordered a few this morning -- they will work fine in a National receiver I'm working on.

    73 - Steve
    KK6IYM likes this.

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