Frozen IF transformer cores. What is your secret?

Discussion in '"Boat Anchor" & Classic Equipment' started by K5MIL, Oct 13, 2017.

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  1. K5MIL

    K5MIL Ham Member QRZ Page

    What is your secret for un freezing the ferrite cores in an IF transformer?

    Bill - K5MIL
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Sometimes, applying heat to the core will unfreeze it. Basically, sticking a soldering iron with a pointed tip into the coil.

    Unfortunately, the majority of time the core is broken. When that happens, you are going to have to use a small probe to "chip out" the core. This takes time and you have to be very careful not to damage the coil form.

    I have run into this situation numerous times. There is a problem in that finding replacement cores may be difficult.

    Glen, K9STH
  3. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    I use a heat gun on "gentle" to warm the coils. Sometimes, people use beeswax to hold the cores in place and a bit of heat will help loosen them up.

    Gentle is the word!

    What radio is this trouble in? The era it was made or brand/model can alter the diagnosis.
  4. K5MIL

    K5MIL Ham Member QRZ Page

    The set is a Collins 32S-1 transmitter, 1958 according to the date on the crystals.

    Bill - K5MIL
  5. KM1H

    KM1H Ham Member QRZ Page

    Using a metal hex wrench will crack cores in a heartbeat, and if it is already cracked it has to come out a bit at a time.

    I use heat plus Kroil; and even a bit of RF on the wrong frequency as a heat source for amp input coils.

  6. KK6IYM

    KK6IYM Ham Member QRZ Page

    I heat up an Allen wrench with my soldering iron and then stick it into the core and let it transfer the heat to the core. Repeat a few times and then I immediately use a plastic hex tool to try and turn the slug. If I can get it out, then I use a different cheap plastic tool to insert into the core and chuck it up in my drill motor. I then turn the core against some emery paper or a file to reduce the diameter a bit. Surplus sales of Nebraska has replacement cores. They are cheap. Getting a broken core out is really tricky and some cores just refuse to break loose. Which transformer is it?

  7. KD2AZI

    KD2AZI Ham Member QRZ Page

    They definitely can if you aren't careful.

    Also, cheap plastic hex wrench can crack them too, if they are low-quaility and prone to twisting. I had to adjust the coils the swan to the left and broke many. I went through a very frustrating period trying to find a high quality set of alignment tools - General Cement were crap. I used baby powder to loosen them up; heat was not an option since the forms looked like they were waxed. I purchased replacement slugs and paper tubes from Nebraska Sales as previous poster. Ultimately I made two hex adjustment tools by molding technique (after consulting the family plastics scientist - they're handy to have around ;)

    This works. Also, you can file the inside of the coil form too.
  8. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    I don't even mess with them unless you really, really need to. I believe in the philosophy that if it ain't broke, don't fix it. :)

    You're more likely to see marked improvements by simply replacing other aged components like out of spec resistors and caps in the same circuit that are connected to them.
    Last edited: Oct 14, 2017
    K8PG likes this.
  9. G3YRO

    G3YRO Ham Member QRZ Page

    These cores are often held in place by the rig manufacturers (after alignment) by a kind of paint/glue . . .

    But this is designed to free up when heat is applied (which is why the soldering iron tip into the core usually works.)

    Roger G3YRO
    K8PG likes this.
  10. WB5WSV

    WB5WSV Ham Member QRZ Page

    For the small ones that use flat screwdriver adjustments I have on occasion removed a cracked one by putting a tiny drop of Super Glue on the tip of a jeweler's screwdriver and allowing it to bond to the core.

    I was building a Ten Tec kit several ears ago and found that the VFO coil cores were good for about two travels over the length of the coil after which they would move up and down no more - it was not tight enough inside. The coils were closed on one end and there was no way to poke them out. I had no choice but to order new coils from Ten Tec.

    When the new coils came I wondered how to keep it from happening again. Then I recalled something I had seen on some GE commercial radios. I took a rubber band, cut it, stretched it though the middle of the coil and the screwed the core in. That made it tight enough that the adjustment capability would not wear out.

    By the way, in order to adjust the screwdriver type it is better to take a suitable size of wooden dowel and file one end to a chisel point. Then lop off the end of the chisel to make it a bit flat and coat the end with either varnish or superglue. That will fit the transformer core much better than a metal screwdriver and is much less likely to crack the core. If you break the end of the dowel off, the just file it again and start over.
    N3AB likes this.

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