Collins 32V2 resuscitation attempt

Discussion in '"Boat Anchor" & Classic Equipment' started by W6BRY, Mar 30, 2020.

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  1. W6BRY

    W6BRY Premium Subscriber QRZ Page

    Hey guys... I found a really crusty 32V2 (1800 serial) locally and made a deal on it last year but after looking closer I decided it needed too much work so I stuck it on a shelf. A few months later at a hamfest I found an absolutely beautiful 32V2 that looks like it has been completely restored so I made a trade and got it home.

    So #1 is the beast and #2 is the beauty.

    I checked out #2 and everything looked perfect so I started powering it up and found the VR75 regulator comes on SUPER bright and within 5 seconds it's so bright it starts turning purple so I did more testing and thought the LV transformer was bad. I ended up buying a new Hammond and it still does the same thing. I've probably spent 20 hours on this thing and I just can't figure out what the problem is. After installing the new transformer I tested the old one and it seems fine... so I'm thinking maybe L301 or L302 is shorted?

    Ok so the longer I worked on #2 I looked at #1 and thought maybe I would try to clean it up and give it a shot and it ends up that old ugly beast is not as bad as I thought.

    I replaced the power cord and built SS rectifiers, cleaned contacts, etc. I fired it up and I have LV and I am able to get B+ and dip the plate successfully.

    At this point I have the antenna connector hooked to a dummy load and I am getting about 30w on tune mode. I don't have the correct mic connector but I figured out a way to get my D-104 connected and now when I tried to get some audio it makes a cracking noise in a nearby receiver. Also makes a cracking noise down near the audio amp tube.

    I found the audio gain pot seems loose so I pulled it apart and cleaned it but I think there is a bushing missing maybe? The brass shaft is loose in the collar so I think I need a new pot.

    The bathtub caps located under the modulator tubes are leaking oil, I have not pulled them out or tested them but I need to figure out where to get replacements or rebuild these.

    At this point I am thinking of pulling the audio/mod assembly out of the beauty and swapping it into the beast. That would take care of the bad caps and the audio gain pot problem, assuming the parts in the beauty are good.

    Well that's where I'm at. Could use some pointers or suggestions on what I should check on the Thermo-nuclear VR-75. Also anyone have a source for parts like the bathtub caps or the audio pot?

    Thanks Brian W6BRY
     
  2. W1NB

    W1NB XML Subscriber QRZ Page

    That’s a voltage regulator tube. It is supposed to glow fairly brightly. Check the bias voltage and if it’s in spec you should be good to go.

    As for the caps in the speech map on #1, you can replace them with electrolytics. Use terminal strips mounted at the screw holes that currently hold the bathtub caps. There are a couple in and around the mic amp and second speech amp stage that will also likely need replacing.
     
    Last edited: Mar 30, 2020
    W1TRY likes this.
  3. W6BRY

    W6BRY Premium Subscriber QRZ Page

    I realize the tube is supposed to glow, as I have cycled it in my tester and it works great. I am also seeing the correct operation when installed in the working transmitter. The glow of the VR tube in the #1 transmitter is like the Sun and gets so bright that it starts to turn pink. I connected my meter to it and it was 105v which is the correct voltage, but it's only supposed to have 40Ma thru it so I am thinking something past it is shorted and allowing it to draw excessive current. I will try to poke around more today and see what I can find.
     
  4. DK7OB

    DK7OB Ham Member QRZ Page

    These tubes are usually run as a shunt regulator (like a Zener diode) with the load in parallel to the tube. So if it draws too high current, there is a problem in the feeding circuit, maybe the series resistor has low value or the feeding voltage is too high or maybe a very low or missing load. A higher load will reduce the current in the tube (and the glow) until voltage drops below the "burning voltage" (translated from German, may not be the correct word) and the tube stops glowing at all.

    At least that's what I remember from my "tube days" 45 years ago...
     
  5. WA3VJB

    WA3VJB Ham Member QRZ Page

    Please consider posting a version of your query to QRZ.com's Amplitude Modulation forum.

    I've had a 32V2 since 1972, and learned that there was a manufacturing defect in the LV transformer. Chronic failure item. The windings were apparently done too tightly, and it took 50 years or so and -x- number of thermal and electrical cycles for the failures to start showing up. I had my rewound by the late Jess Price in 1973 or so.

    For any continued problems, the AM Forum that I recommended has many, many users of this transmitter who may have some troubleshooting advice.

    Hope you get both beasts on the air some day.
     
  6. W6BRY

    W6BRY Premium Subscriber QRZ Page

    Thank you all for the replies, I will post to the am forum.
     
  7. W1NB

    W1NB XML Subscriber QRZ Page

    That tube regulates the bias, not the low voltage. It’s a VR-75 so you should be seeing -75V, not 105V. You may be seeing -105V somewhere in the voltage divider but you shouldn’t have -105V of bias.

    If the transformer were experiencing issues, like some shorted windings, the secondary voltage, and thus the low voltage and bias, would be lower than it should be. If you are seeing 240V under load for low voltage and maintaining -75V bias then I would think the transformer is fine. I may be wrong but I thought the inherent premature transformer failures were manifesting themselves as openings in the windings, which would cause a complete failure in both the LV and bias.

    I am a bit confused as to which radio (1 or 2) is experiencing the issue. I thought you said it was #2, the clean one you recently purchased. In the response above you said it was glowing brightly in #1, not #2.
     
  8. W6BRY

    W6BRY Premium Subscriber QRZ Page

    I'm sorry about the mix-up, yes it is the pretty one that has the problem with the regulator tube.

    My neighbor is a broadcast engineer and long time ham so I was able to talk him into coming over today to look at the radio. We played with the ugly one for a while and got it working real good on CW but when I switch to phone it is arcing in the modulation transformer.

    I packed everything up on the ugly one and moved it off the bench and got the pretty one back up to work on it. We re-tested my old LV transformer and confirmed none of the windings are shorted to each other or to ground. Then we removed all the tubes and tested the voltage at the VR tube. I measured -315v on pin 2 which makes no sense at all, but does explain why the VR tube is getting so dang hot!

    After looking everywhere trying to figure out where the problem may be, I thought maybe someone had wired the LV transformer incorrectly as I simply copied the wire connections when installing the new transformer. I decided to put the old transformer back in so I could trace each connection and verify them all. I then tested all wiring connections and finished installing the original transformer.
    Looking at the schematic it seemed like every possibility for the -315v on the VR was tested and ruled out, but then we noticed the board at the rear that has the rows of resistors is giving some strange readings.

    R307 & R311 are wired in parallel but when we measured across them in circuit I see only 30 ohms across the pair. When I clipped one lead I am seeing 100k as expected, so something on either side of these resistors is shorted.

    We tried pulling things off the board and also tried running the wires all the way to the meter function switch and still couldn't find the problem.

    At this point I had to take a break and I'm going to order all of the resistors on that board at the rear and replace them so I know the values are correct.
     

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