KWM-2 Restoration Project: what next?

Discussion in '"Boat Anchor" & Classic Equipment' started by KJ7MX, Dec 7, 2019.

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  1. KJ7MX

    KJ7MX Ham Member QRZ Page

    I recently acquired a complete KWM-2 station (KWM-2, 516F-2, 312B-5, 30L-1) that belonged to an uncle who was the original owner. Although it's in very nice physical condition, it's in the "sat in a closet for 20 years" electrical condition. Well, mostly a garage, and everything is filthy. The KWM-2 worked the last time it was used, and now it doesn't - imagine that!

    What is happening is when powered on, I get dial lights, and the tubes light up except for the finals, which appear to have a very dim glow. No audio from the speaker or the phone jack, and no relay engagement when attempting to switch the rig into xmit. Before I ever powered it up I recapped the 516F-2. I've also cleaned the contacts on all three relays: the two plug-ins underneath and the one in the final cage. I brought the rig up on a variac after recapping the power supply, saw these results, and then installed a recap kit (including the can) for the KWM-2. After recapping both I'm getting the same exact results mentioned above: no smoke, but not much of anything else either. As luck would have it my B&K tube tester went south a week before the station arrived so I'm unable to test tubes at the moment. I highly doubt these issues are related to a bad tube, and more than likely it's multiple failures points at the moment.

    So...just curious if anyone might have a suggestion based on this information? I do ok with alignments and cleaning the internals switches and controls, not so much with troubleshooting. Unless there's an "AH HA!" step I'm missing, it will most likely get sent off to one of the Collins experts who can bring it back to factory performance.
    KL7KN likes this.
  2. KL7KN

    KL7KN Ham Member QRZ Page

    I would pull the tubes and clean the pins - as dumb as that might sound. Ditto for the tube sockets. Ditto for the crystals and sockets.

    If this has been sitting for that extended a period of time in a non-climate controlled area, oxidation would be a concern.

    You did good to recap the P/S.

    Please post updates, while I once owned a station just as you described, before going all solid state, I don't miss having it in the shack. These really are a classic piece of gear, if just horribly's just that there are so many better radios today.

    Best of luck!
  3. KK6IYM

    KK6IYM Ham Member QRZ Page

    These radios look very complicated: however, like everything, they can be understood one area at a time. I would suggest you do not activate the transmitter until you get the receiver working. The first thing I would do is check all the tube pin resistances, then if those check out, the tube pin voltages—except for the finals. When you say that you don’t hear anything at the phone jack—do you mean nothing at all? That would indicate a problem with the audio stage and that should be checked out first. I have found that many times the reason the radio was put in the garage in the first place was because it stopped working for some reason.

  4. VE2GCE

    VE2GCE Ham Member QRZ Page

    I recently restored a KWM2 and it did not work after I plugged it in initially.

    For idle rigs, I find you have to do the following two steps as a minimum.

    1) Clean oxided electrical contacts
    Get yourself a can of contact cleaner, unplug each tube in turn and spray the socket.
    Then spray the variable controls and finally spray all the rotary switch contacts.

    2) Paper and electrolytic capacitors dry out and usually need to be replaced after 50-60 yrs.

    If the rig worked before storage, the tubes will still be good.
    At this point, if you get life out of the rig, you can align it for maximum performance.
    If it is still not working at this point, check the voltages against the service manual troubleshooting chart (available on the Collins Collector website).
    Last edited: Dec 7, 2019
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd encourage you to join the Collins Collectors forum also:

    Unless the rig's been dropped or something dropped inside it when the cover was open, I doubt "tubes" are a problem. Tube contacts can definitely be a problem, as can contacts on all switches.

    If it sat in an uncontrolled environment for 20 years, there should be lots of oxidation on what were once silver-plated contacts all over the place. I'll bet the dial string that works the LOAD control (which is only active when transmitting, not receiving) is either broken or will break when you go to use it.:)

    "No audio" from speaker or phones can easily be oxidation/dirt on the phone jack contacts, which are in series with the speaker when phones aren't plugged in and still need to work when phones are plugged in.

    There's hundreds of things that "might" be wrong, but taking data and writing it down so you're not relying on memory in discussions, and then asking questions on the Collins reflector can bring wonderful advice. I'd do that.
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Over the years, I have worked on a fair number of Collins KWM-2 and KWM-2A units.

    Although it can happen, I have never had to replace the dial cord that is used to tune the antenna loading capacitor. Collins used some very good cord and, even after several decades, is virtually always in good condition.

    Since you replaced the capacitors in the 516F-2, go back and make sure that they are installed properly. There are a couple of capacitors that have the positive terminal, not the negative terminal, grounded. These are in the bias supply. Also, did you replace the selenium bias rectifier? This needs to be replaced and a 1N4007, very cheap, diode works very well. Make sure that the cathode (end with the line) goes towards the transformer.

    Make sure that there is the lower B+ voltage present. You will not get any sound out of the unit if this voltage is not present. The wire, for this voltage, might have been accidentally disconnected in the power supply or it may have gotten broken in the 11-pin connector on the end of the power cable. A good indication as to if the lower B+ is present is if the "S" meter goes to the pin and then, slowly, goes back to zero when the r.f. gain control is fully clockwise.

    There are several paper capacitors and electrolytic capacitors in the unit. If you haven't replaced them, do so. As in the power supply, there are a couple of electrolytic capacitors with the positive terminal connected to ground. You don't need an expensive "can" to replace that capacitor. It is MUCH cheaper to disconnect the terminals and then use discrete capacitors. Remember, "modern" electrolytic capacitors will have slightly different values than the older type. Instead of 20 mfd, the new one will be 22 mfd, instead of 30 mfd, the new one will be 33 mfd, instead of 40 mfd, the new one will be 39 mfd, and so forth. Using a capacitor with a slightly higher mfd will work fine. The original capacitors usually had a tolerance of -50% / +80% and new ones will have tolerances of +/- 10% or +/- 20% either of which will work fine.

    Turn all of the VOX controls (located on the shelf just behind the front panel) all the way counter-clockwise. If these are set too high, the unit will be in a transmit mode and there will be no sound coming from the speaker.

    Clean the tube pins. I dip them in Goddard's Silver Dip or Tarn-X. Use one of those very small brushes sold for cleaning between your teeth to clean the tube sockets. You can dip the brush in Goddard's or Tarn-X or use DeOxit (I really do not like that product and do not use it).

    The center of the RCA jacks do become loose over the years. Use a pair of needle nosed pliers to slightly compress the contact from inside the unit.

    It really doesn't do much good to use a Variac because, unlike a fully sold-state power supply, the 5U4 and 5R4 rectifier tubes do not really start working until around 100 VAC is applied to the supply.

    Slightly loosen, and retighten, all of the connectors that go through the chassis because all of the grounds are made through these connectors. This includes the machine screws that hold the tube sockets in place.

    Clean the switches and potentiometers (i.e. r.f. gain and a.f. gain).

    Clean the relay contacts using a cleaner on strips of computer paper, etc. Do NOT use a file, sandpaper, etc. If the relays are wire-in they are going to be a pain in the posterior to clean. However, such is necessary. If plug-in, remove from the socket and then use a small screwdriver inserted at the bottom to remove the plastic cover. These relays are easier to clean. After cleaning, the cover will "snap" into place as it is returned to position.

    Make sure the brown 9-pin plug is inserted in the socket to which it will just reach because of the metal chain attached. Do not plug in the 312B-5 until you get the unit working.

    Check the contacts on the phone jack. If these are dirty / not making contact / etc., there will be no sound from the speaker.

    If the audio output tube is dead, there will be no sound even a "hum" coming from the unit. Otherwise, even if there just happens to be a bad tube, there should be some sound coming from the speaker.

    Of course, make sure that the speaker is working. A dirty switch in the 312B-5 can "kill" the speaker.

    There are other possibilities. However, all of the above need to be checked before getting more involved.

    Glen, K9STH

    technical adviser-1a.jpeg
  7. KJ7MX

    KJ7MX Ham Member QRZ Page

    Thanks guys - lots of great tips!

    For some reason I just felt there was something going on in the power supply so for the heck of it I ordered a new pair of tubes for the 516F-2 and that cured the problem! Specifically it was a bad 5u4.

    Glen - thank you for that info on the variac and the power supply tubes - that is some good information that I was not aware of. So basically I recapped the power supply, replaced both tubes, and recapped the KWM-2. All relays were cleaned using deoxit and strips cut from cardstock (think business card). I also pulled each tube and cleaned the pins using tarnx with a denatured alcohol rinse. With the new tubes installed in the 516F-2, the receiver immediately came to life and man, is it hot! Unbelievable. I let it warm up for about 15 minutes and tried transmit. It loads perfectly on all bands with output between 85 watts on 10 and around 110 watts on 80. For now everything appears good - not even any scratchy controls, which I find odd since it had been in storage for 20 years, with the last 6 or 7 in only a semi climate-controlled environment. None of the pieces have any obvious signs of oxidation, so that's good too!

    The full story on this station is that it belonged to my elmer and uncle, Norm, W0KCJ, who became SK in 2016. Around 1998 or '99 he gave the station to his brother as an enticement to get back on the air. It was used briefly and put away, then moved from closet to closet, and finally to the shop. When I passed my general at age 13 in 1978 I would visit Norm and was allowed to run the Collins gear under supervision. Doesn't sound like a big deal these days but man when you're 13 years old and that gear was still in production it's about like being given the keys to a new BMW. Well, it was for me anyway!

    I got a call last summer from my other uncle who had the gear saying that if I wanted the Collins station to come pick it up. Before Thanksgiving we flew back to Minnesota, packed it up, and shipped it back out to Olympia, WA. It's not in the pristine condition it once was, but the front panels are perfect on all pieces, and after spending several hours cleaning cabinets, chassis surfaces, etc, the most it will probably need is some refinishing of the trim rings to make it look near new. The SM-3 was missing the small emblem on the end of the mic and someone had pushed the screen in to make it basically "flat". I couldn't believe it that someone on eBay was selling a replica emblem for the SM-3 for $6 so I bought one and spent a couple hours bending and reshaping that dang mic screen until it's hard to tell it was ever deformed.

    So, hoping the KWM-2 holds together and this isn't a flash in the pan. My next project will be the 30L-1. I've got the replacement PS board from Harbach on the desk with new tubes coming this week. When all is said and done it will be pretty cool to have the station I was only allowed to use under supervision back up and running, forty years after the last time I used it!
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Don't try to use the KWM-2 on CW. Unfortunately, Collins used side-tone CW generation in the KWM-2, KWM-2A, 32S-1, and 32S-2. That method produces at least 3-simultaneous signals and can, under some circumstances, produce 5-signals. For SSB, the KWM-2 / KWM-2A is excellent.

    There can be a slight frequency shift between transmitting and receiving with the KWM-2 / KWM-2A. There is a fairly simple modification, often called the "Vietnam modification", to correct this. Although never "officially" adopted by Collins, this modification has been widely promoted. Instructions on doing this modification can be found at the following URL:

    Glen, K9STH
    W4NNF likes this.
  9. KJ7MX

    KJ7MX Ham Member QRZ Page

    Here's the progress so far: the KWM-2 and power supply. All cleaned up & checked into a few nets with good reports. A few gremlins are showing up, but nothing to worrisome. Relays are going to need a round #2 cleaning as they don't always go back into full receive. The USB audio is "tinny" sounding so an alignment will be done once all the other pieces are up and running.

    Next will be the 312B-5. I hooked it up to the KWM-2 to see where things were at & the vfo switch dies when it's set to receive/xmit on vfo #2 (external). I got as far as verifying continuity in the vfo cable is ok, so it looks like more switch cleaning will be in order.

    So far, better than expected! IMG_0487.JPG
  10. KJ7MX

    KJ7MX Ham Member QRZ Page

    I've now got the 312B-5 up and running a-ok. All that was required was a little cleaning and it came to life.

    I also just wrapped up (I hope) the 30L-1 after installing the Harbach power supply upgrade and a new set of tubes. It turns out Surplus Sales of Nebraska has a limited supply of the original Cetron 811A's. Even though they were more expensive than the Chinese Taylor tubes, I was still able to get a complete set for $210 shipped. The initial power up went smooth with just under 2k volts at idle. Tomorrow I'll put it in line and see if she'll load up. Here's a shot of the inside with the new board and tubes installed 30l-1 pt 2.JPG

    And here's a shot of the old caps, you think it was time for an upgrade????

    30l-1 pt 1.JPG

    If all goes well tomorrow the rest of the project will be cosmetic. There appears to be some sort of electrolysis scars on the face of the watt meter for the 312b-5 and the meter for the 30L1. I found a seller on eBay who makes an adhesive vinyl replica of the meter face for the 30L-1 so I ordered one to see if it will do the trick. Surplus Sales has the 312b-4 / 5 watt meter although they're quite expensive. They're NOS so will probably end up ordering one.

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