Transformer potting material??

[ThSpeakerDude88]

Ok I have an RCA 5t am reciever I'm restoring.

The trafo has puked its guts, because someone added solid statde diodes across the rectifier causing extra stress on the trafo. The trafo also has cloth covered wiring that is deteriorated, and is unsafe.

I'm looking for a replacment transformer, but I was wondering if the tar in the transformer is safe or not?

my main question: Does this tar contain PCB's? If not I will just tear down the transformer and clean it up and repot it.



Thanks for any help,

TSD88~

[jlsem]

Does this tar contain PCB's?

No, it's just tar. Dirty, messy, sticky tar.

John

[ThSpeakerDude88]

Phew~! Ok so after reading that , I've removed most of the tar from the case. Now to dissasemble the transformer laminates. Its tiered in 3's, so it should be easy.

[ThSpeakerDude88]

alright so today I removed the rest of the potting, I tore apart the laminates and cleaned each one with paint thinner and SOS. I unwound the 5vac and 6.3vac taps on the core because the wires to them were so messed up, and the tar was so goopy it would have been impossible to get to them. Its just 22gague coated wire, so I'll just rewind it. I measured the 5vac wire length at 183", and the 6.3vac at 229 inches for rewinding.

[poobah]

Don't go bonkers using abrasives to clean the lams... they have an insulating coating... silicon compound I believe. If they are bright shiny steel now... you have issues.

This coating is to minimize eddy currents. There is a fix though... one coat of clear lacquer before re-assembly will do the trick.

What is the appearance of the lams now?

[Tweeker]

PCBs reek. If it smells like johnny cake/mothballs or menthol, youve probably got PCBs. There are tarry heavily chlorinated PCBs that saw use as potting material, but they reek, and tend to be labeled with a PCB trade name as the PCBs were a selling point that cost more.

[ThSpeakerDude88]

eh, about the same as a new transformer, only more tarnished. Actually there wasnt any tar between the lams they were pretty clean, just rusty.

anyways........ Well the trafo still gets hot when i plug it in , even with no load... I'm still getting the right voltage reading ( 338v-0-338v) a little low from the 345 but I guess thats to be expected. The transformer still hums ( as it did before) , its too hot, unsafe....

bah..

I think I'm gonna ditch the field coil speaker and get a regular one, which will allow me to drop the B+ by 100v. So all I need is a trafo that will get me 255v. I've found some hammonds on tubesandmore that I think will work. Heres one question, should I do away with the LC filter ( field coil is the choke in this case) and just use a simple RC network or should I actually order a choke ?

[kevinkr]

I'd keep the field coil speaker unless it is totally roached. I imagine that a suitable Hammond transformer to replace the current one would probably cost less than the choke/speaker/transformer combination you propose.. Plus is this a "restoration" or something else?

The other alternative would be to get someone like Peter Dahl or Electra-print, audio transformers or a local to rewind the existing one.I am pretty sure you have a partial short in one of the windings, most likely the high V secondary. There are several vendors listed in Audio Express that can do this sort of work.

Good luck

[sorenj07]

Always order a choke if you can. It's always worth it. They do a better job of filtering hum than resistors, no question.

[kevinkr]

Another thing to consider about the fieldcoil speaker that was originally installed in this thing is that it is probably far more efficient than most reasonably priced pm speakers that will fit..