Mouse House KWM-2A - Ugh....

Discussion in '"Boat Anchor" & Classic Equipment' started by K8CCA, Jun 7, 2021.

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  1. K8CCA

    K8CCA Ham Member QRZ Page

    Went to the first hamfest in a couple years on Saturday, and found a poor KWM2A that was the former residence for a mouse family. I ran across the gentleman selling this first thing in the morning, and he was asking $500 for the radio, power supply, and the remote VFO 312-B5. All had been stored in a garage for years and where very dirty, with the previously mentioned inhabitants. I decided to pass, but was thinking about it all day. Was getting ready to leave and decided to see if it was still there and it was. Well after a bit of negotiating, I now own it. I dragged it home and spent the day removing mouse turds and years of nicotine. I think that the nicotine coating actually saved this old radio. It cleaned up pretty well and I am pretty optimistic about getting it on the air. I will replace all the electrolytic and paper caps before I fire it up. Here are my first observations/questions for you guys:
    1. Some of the tubes do not match the markings on the chassis ie V7 has a 6DK6 vs 6DC6 but they all look to be a good substitute according to this page https://www.nostalgickitscentral.com/info/tubexref6.html. Why do people sub tubes and not just use what Collins had designed it for?
    2. This one has me really stumped. There is a 10uF Electrolytic cap paralleled to ground with a .01uf Ceramic disc cap C263 from pin 7 of tube V1 6AZ8 (first mic amp). It was obviously not a factory cap, but very old Sprague "Atoms". I have not read thru all the service bulletins, but was this a standard mod? I thought at first perhaps it was a black beauty cap that somebody had read the stripes wrong at first, but now I think it might be a mod. Any thoughts?
    Here is the schematic
    [​IMG]
    I think I am going to order the Hayseed hamfest can cap before I fire it up.
     
  2. KJ4YEV

    KJ4YEV Premium Subscriber QRZ Page

    That was probably somebody's mod to "fatten" up the bass response a bit.
     
    KP4SX likes this.
  3. N8YX

    N8YX Ham Member QRZ Page

    A little off-topic:

    Look up "bucket trap" if you have a garage or other space where critters like to get in and make a mess of stored equipment, autos and so forth. I can tell you from experience they work very, very well at drawing the attention of mice away from things you don't want destroyed.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Possibly it was a branch of the Mickey Mouse Club.

    I had a crush on Annette Funicello when I was about 8 years old and would have invited her into my KWM-2 any time, although I didn't have a KWM-2 at the time.
     
  5. WA1GXC

    WA1GXC Ham Member QRZ Page



    My first rule of Amateur radio acquisition: Never assume the clown who used your new-to-you radio knew more stuff than you do.
    It usually ends in heartbreak. And your cash has already crossed state lines.

    The first thing I do is go over it for a close visual inspection noting components that don't appear contemporaneous. For those who've been around
    a while, it's easy to spot ringers like Orange Drops in place of Sparague Atom or Acushnet AccuCaps.

    Then it's on to identifying anything out of place or time. All "improvements" get stripped-out and restored to factory schematic configuration.

    Your "improvement" is interesting. I bought a 1966-build Collins 75S-3c in 1985. All excited. I was younger then.
    Noted after a couple weeks the 6BF5 audio output tube was glowing dull-medium orange. On the plate.

    Seems my ham-genius ran with your crowd. 10uF electrolytic across the cathode resistor to ground. Must have been a common
    hint for the gifted.
    Removed it, threw it out, vacuum tubes all back to normal. Cooked and cracked the 5w cement power resistor in the P.S., way over-stressed
    a bunch of stuff.

    73
     
    KP4SX likes this.
  6. W1NB

    W1NB XML Subscriber QRZ Page

    I’ve not experienced this but I’ve heard other hams claim the 6U8A tubes are very prone to soft failure so it’s not uncommon to see them substituted with 6GH8S or 6EA8s.

    As KJ4YEV pointed out, the electrolytic was almost certainly installed to help boost the low frequency response in the speech amp.
     

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