BC-610 h Talkback ,Baking Transformers

[ve8xj]

I have tried a lot of thing as of late to stop my 610 from squawking at me . I recently moved into a different room for my shack and cannot escape the talk back  entering the audio chain and starting a feedback loop. Both the high voltage choke and mod tranny are like speakers.

Thing tried :

-Capacitors across all relays(moderate success ,perhaps 30%reduction)
-Isolating mod tranny from ground(useless)
-Built box for mod tranny and mounted externally (worked great ,but awkward and not at all the long term solution I was looking for. However choke still squawking)

The next thing I would like to try is baking the transformers  to redistribute the tar. Both the choke and mod tranny have hollow spots at the top when you tap on them . I would imagine this is undesirable,and a sign that the tar inside is all dried up and probably not doing it's job as well as it could.

Any advice on temperature and time to bake these suckers back to spec. I'm thinking pretty low temps but perhaps one of you has real experience in doing this.If I can get that tar between those laminations again I might have a chance . Had this junk pile apart so many times that it is losing it's charm on me and becoming a curse. If I had hair I would have pulled it out by now. 

Advice welcome please

[KL7OF]

I have never baked a transformer enough to make the tar liquid enough to flow.....I don't see why it can't be done however..If you could get a sample of the tar from the txfmr and see how hot you have to get it to make it flow then you will know how much heat you need to do the job. You have to consider what this heat will do to the other components of the txfmr as well as the tar....I reckon a domestic oven would do the job...Probably better if you used an old one out in the woodshed rather than the one in the kitchen....gonna be stinky..A buddy of mine once repaired a mod txfmr by digging the tar out around a broken wire enough to get a splice on there and then he filled the voids with transformer shellac...I don't know where you would get transformer shellac....I wonder if you could heat up the transformer  some and then just pour melted tar in there or shellac in there...  ...I want to hear that BC 610 on 20 meter AM this winter.......Good Luck...Steve

[K3YA]

Years ago I had a BC-610F with a noisy mod transformer.  Most of the noise seemed to be coming out of the top of the can, which had little tar under it.  I clamped a piece of plywood against the top, held down with all thread run back through the chassis.  I think I used some Moretite or some similar putty between the wood and steel top. This damped out most of the talkback and was easy to do.

[WBear2GCR]

I cleaned out a small can tar filled xfmr in my "industrial use only" electric kitchen oven (really, got one for noxious baking only) at a temp of <212deg F...


... but the can likely has a solder filled hole, I'd make sure that this hole is open before heating the xfrmr, as it might bulge a bit...

another trick would be to solder on some copper tube and hook that up to a vacuum pump... once the tar is hot that will pull all the air bubbles out of the tar and windings... a vacuum pump is also the input side to an air compressor...

but if the moretite or maybe silicone rubber and a plate works, that's simpler...

Also have you tried an isolation mounting set up for the mod iron? You can test that idea by just taking the bolts out and inserting somethings squishy (medium soft rubber for example) under the iron and between it and the chassis.

Hope this helps.

                           _-_-bear

[W2PFY]

I had a BC-610C model transmitter and it's mod transformer also talked back. My happiest day is when it blew out with me ringing chimes through it. I replaced it with a multi match at first and later got a nice open frame 610 transformer from K1KBW and it was quiet. I think the sealed ones are more prone to talk back than the old open ones with the end bells on them.

[AB2EZ]

Something that worked for me... and is easy to try:

My KW-1 had a very large amount of talk-back. The whole cabinet was acting like an excellent loudspeaker.

I removed the bolts holding the mod transformer to the cabinet. I placed a soft, spongy 1/4" thick computer mouse pad under the transformer. Obviously, gravity held it in place.

The talk-back was reduced to the point where it was not audible.

Stu

[ve8xj]

Thanks for all the advice gentlemen !

Sounds like before I try this I will have to find an oven that I don't mind perhaps getting contaminated with whatever is in these things if there is an accident . My wife would not be impressed if I got her nice gas range all gooey .
Every spring here the town hold a spring clean up and all large garbage is hauled away free of charge . This is a great time to keep an eye out for a transformer oven . Must be over a hundred thrown out every year because the colour did not match the reno.

The vacuum idea is also something I would like to do if I do this that makes a lot of sense but could be tricky in the kitchen .
 
 I imagine when these transformers are made the tar would have been all the way to the top ,but years of high heat from the tubes settles the tar as well as evaporates any solvent that might have been in the mix.

I think you are right that the potted transformers seem to be a lot more prone to this problem and I will for sure keep an eye out for a older style one . If there is room for one in there.

  Right now the mod iron is in a plywood box 12"x12"x16" with foam rubber all around it sitting behind the 610 out of site. It certainly works well now ,but it is a band-aid solution at best . I am however content with this till I find an easy bake oven big enough for the choke . I might in some spare time though try K3YA's clamping solution. Which is simple and could be very effective. Wish I had thought that one up myself. That is why this board exists I guess.

Something else I noticed yesterday as well when working on this problem was that the safety interconnects for the 110v which are placed on the top hatches
are also producers of talkbalk . Mine are the metal slug type which when closed rest in a V type trough to make contact . The area of contact is so small though that it is constantly pitting the slug with an arc. Same for the one on the back cover . Also if you do not put all the bolts back in the side and back covers the holes will spit modulated sparks. FREAKY ! What a TVI monster .

  I have actually been dreaming of redoing this 610 in a totally different way . Having the transmitter ,modulator and power supply all in individual cases . More of a desk set-up, with the PS under the table . It would take a while to make the harnesses but could be worth the effort . Allowing one to properly TVI proof the unit. I would use shielded cables for most runs ,build a cage around the RF deck etc etc. Wouldn't be true to the original but would be pretty easy to restore if I kept all the old harnesses and cabinet. But I have a lot of other projects on the go before I try this . As well not to sure I want to tamper with a piece if history like that.

By the way I have tried to isolate the mod transformer from the cabinet at least from ground potential with a plastic gasket and plastic washers around the bolt posts . To no avail though. But it was not a soft gasket and would not have stopped vibration . Perhaps something else to try .

Should be on 20m this weekend if we have condx . Been great up until 2 days ago. Go figure eh?