Tin box of HMV Gramophone needles in Top unused condition.
Free, last week I bought a couple of boxes of Kriesler parts and they were in the box. As my interest is only TVs and Radiograms I have no use for these. So if you want them put your hand up and I post them too you, if no takers its in the bin.
Pete.
Now how did I go with the box of parts ?
Every speaker Transformer was stuffed!
Some nice odd bits though, badges etc and 1 good Alnico Rola speaker .

a couple of boxes of Kriesler parts ... Every speaker Transformer was stuffed!

Not surprised. Kriesler speaker transformers had a high failure rate. I've mentioned before that it would be instructive to perform post mortems on a bunch of them to determine why they fail.

Hi G , mostly they were Rola. But I spoke to a guy called David who runs a vintage radio transformer re winding service in Victoria and he really knows his stuff about Transformers. He said that the lacquer coating on the wire gets cracks in it, Then corrosion forms and resistance increases and eventually it leads to a dead transformer. Lucky I do not need any Transformers at the moment and the boxes I bought was only just for extra spares.
But he is re winding me a Transformer for anther project that has been sitting in waiting for years. But I dont need any for my Krieslers touch wood!!

Hey Pete I wouldn't mind the needles . Happy to pay postage or send you some caps.

All yours Carl, send me your address and I will pop them in the post for you. No need to give me caps etc etc, I just dont want to put them in the Bin and I'm not into Gramophones.
All the best Pete

Re Speaker Transformers failing by going O/C.

A long while ago in PMG days we had our own Workshops for making all manner of things and one of their roles was to rewind relay coils and in some cases actually make relay coils.
When some of their rewinds were suddenly failing in use they started to look into it and discovered that the winding guys would often/always use a small piece of Scotch/ Bear/ (whatever you want to call the clear general purpose) sticky tape to hold turns in place so they could bring the leads out to terminate on the tags.
About that same time in the early 1960's Rola also discovered their speaker transformers were going O/C. With both lots looking at a similar problem they collectively worked out that the adhesive used on the tape would soften and almost dissolve the enamel coating on the rather fine wire and then eat into the copper finally making the wire go open or very high resistance.

Was quite obvious with a relay coil as through the often clear outer wrapping you could see a small spot of green verdigris and at that point the wire would be open circuit.
Often in the field as quick fix we would remove the outer wrapping, remove the corroded section of wire and unwrap enough turns to be able to re-terminate the wire onto the relay coil tag and we would be back in business.

Had done that myself on a few Rola speaker transformers where the corrosion was obvious.

Lindsay

Hello Lindsay,
Interesting, Because all those 60s Rolas use that type of Tape under the first layer of paper.
We all have experienced the disappointment in restoring a Radiogram or Radio only to find the speaker Transformer is stuffed and then comes the often impossible job to find a matching one.
Im only a beginner with electronics ,but I have read a enormous amount on transformers as it interests me and I have also spoken to guys who are experts with this type of thing.
But just as GTC suggested I will open a couple up take some pics and see if I identify at what point the Transformers are becoming O/C .
On the advice of Ian and a Article I read about heating transformer up in the oven and the dipping them in polyurethane to preserve them , I chose to Dip my good transformers in polyurethane.
Pete

they collectively worked out that the adhesive used on the tape would soften and almost dissolve the enamel coating on the rather fine wire and then eat into the copper finally making the wire go open or very high resistance.

Puts me in mind of Telstra's "Seal the CAN (Customer Access Network)" debacle:

QUOTE: In 1999-2000 Telstra embarked on a campaign to try and encapsulate its network. It was called Seal the CAN 2000. Some of you may be familiar with that. Its concept was great. The idea was fantastic. But in practice it was miserable. Unfortunately the [3M] encapsulant that was used ended up attracting the water and had a non-desired effect, actually accelerating corrosion of the copper network once it was installed. That was done on a proactive basis. Members and employees in Telstra were told, and they were policed around this stuff, if they did not encapsulate the whole of the network—every time you went into it, you were asked to encapsulate it in this gel substance. If you did not, you were disciplined. That went on for six years, despite the fact that the union and the actual employees themselves were continually telling Telstra, 'Look, this is bad for our network; we need to stop this practice.' It wasn't until 2006 that we saw a national ban actually stopping this.

. . .

It has got to be chopped out and the joints remade. So there is another problem, in that not only do they have to remake the joint but they have to pull new copper in to facilitate a joint so that they can get rid of that gel affected network. The gel had a habit of actually making its way down, up to 1½ metres, into the copper network. In fact, it would go down into the pipe entry points inside the pit, so remediating it on the spot became impossible. (John O'Donnell Communications Division, CEPU, to NBN Select Committee in 2014).

RE Autopsy on 60s Speaker Transformers to try and understand why they have such a high Rate of failure with O/C . Both Kriesler and Rola from the early 60s seem to have a high fail rate.
So I have 2 Transformers to strip down and see if I can see where things are going wrong due to corrosion? Or whatever It may be causing it.
This is not intended to repair of a Transformer, Its only to help me understand why they are so prone to O/c and a good chance for me to learn something.

Ok 1st Transformer is a
ROLA K9 1960 , 7k 2ohm.
Readings
Primarily is fine and has continuity.
Secondary is Open and has no continuity.
No shorts bewteen primary and secondary on any leads.


2nd Transformer
Rola 1958 K9,, 7k 2ohm.
Readings
Primarily is O/C
Secondary has no continuity.
No shorts between secondary and primary.

I will start with Transformer No 1

On removing the first paper covering to expose the windings I see No corrosion. I see a cotton tape under one end of the winding and its of a non adhesive type and is in excellent condition.
I do see dark Tarnish spots on the Primary winding.
Which makes me wonder is this were the breaking down starts? Are the coatings breaking down?

After Removing the primary windings , I tested the secondary again and there was no continuity.
There is layer of very light type plastic paper between Primary and secondary, This is also in good condition.
After Removing that plastic paper I then have a layer of Wax paper which is extremely soft , wet ,sticky.
After Removing the Wax paper I can plainly see where the coil windings are broken.
It is not near any tape ends.
But the interesting thing is the Windings are brittle, rotten!
Although I cant see a corrosion by eye , They have rotted! By a corrosion of some type and are breaking up in many places.

Im wondering this? If the paper that was used is not Acid free than it would more than likely contain Chlorine dioxide
Which turns paper yellow and eats copper in time !!!!
We have yellowed paper and rotting copper, a corrosion of some type. See pics!!

Well , lets wait and see whats going on in number 2 Transformer?
Im sure there are plenty of people here who are experts with Transformers who can shine some light on these Rolas.
Pete

1 https://imgur.com/a/Y7EBjyK

The DC voltage on them hastens the demise through electrolysis.

I reckon if you have a good one, soak it in oil-based Estapol or similar and bake it in a warm oven.

I've found a good source of quite well made single ended speaker transformers out of the States. They actually have them made in Mexico. For push-pull circuits you can use a number of Altronics PA speaker matching transformers. No good for SE circuits without first gapping the core.

Hello, Ian
I dont need one , I have good ones and spares too,but I'm going through that box of parts and the topic came up of 60s Rolas and Kriesler speaker Transformers mostly always being O/C so I was wonder why by looking inside one.
Hope your well, Pete

Good work Pete.

Brad, can you possibly move this to a new Tech Talk thread titled 'Output Transformer Failure Modes'? (I took it off topic from gramophone needles).

"But the interesting thing is the Windings are brittle, rotten! "

The observation that the copper wire appears brittle without any green corrosion product (verdigris) makes the type of the corrosion appear to be intergranular.

All metals are made up of small individual crystals of metal (except some very specialist products made from single crystals and glassy metals). Something like a sugar cube made up of individual grains of sugar. The boundaries between individual grains are disordered compared to the crystal structure of the body of the grains (which for copper is a cube with an atom at each corner and the centre of each face - face centred cubic).
This difference in structure means that the grain body and grain boundary have different electrochemical potentials. So given the right environment the grain boundary can be attacked electrochemically. In transformers this seems to be sulpher compounds in oils used used in transformer oils, or probably in this case oiled tape or paper. Because the grain boundary is only a few atoms wide very little corrosion product is produced. If the corrosion goes right through the wire then it becomes brittle. (In some cases of intergranular corrosion the metal literally falls apart ie the sugar cube goes back to a bowl of sugar).

There may be other chemical causes - corrosion can be very subtle in its causes.

Thats interesting STC..
Bleached paper or Acid paper also has sulpher in it by memory.
Its been years since I had to do any chemical study .
I will know more when I pull the other one down as to whether the Transformer mentioned about is perhaps a one off issue?
Monday is my day off work so I will have a look at the other Transformer just for fun.
Its just a way of understanding what maybe going on in these old Rolas , because we do have transformers that are 80 years old and still working.....Pete

I couldn't find an exact description of your sort of failure, only other failures and general descriptions of the mechanism. I suppose water must be involved for the ions to exist in for corrosion but that wasn't mentioned. If so a good drying before applying the polyurethane should help. Excluding air should also help but a bit harder - would require putting the transformer in a pot of the polyurethane and applying a vacuum. when the vacuum is broken atmospheric pressure would drive in the polyu.