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Quad II Output transformer rewinding question

I am in the process of having some Quad II output transformers rewound and have unwound a faulty one and can confirm that the basic arrangement is as shown here




(As mentioned later in the post there is no connection between Z-U or W-X)

The laminations are TU and measure 90X62mm with a 42X22 window. They are alternated with no stacking. There are in effect 14 windings, 8 primary and 6 secondary. Each of the primaries consists of 3 layers of 160 turns and each of the seconderies 1 layer of 51 turns.

I don’t have a wire guage to hand but each layer is full, the bobbin is 38mm wide and 160 turns of 34 swg = 0.2337mmX160 = 37.4mm however 51 turns of 24 swg = 0.5588mmX51 = 28.5mm, but 22 swg = 0.7112mmX51 would be 36.3mm which is much closer.

The 3 bottom seconderies are in parallel and the small wirewound device is inserted between the top of the 3rd and 4th windings.

The winding arrangement is p-s-p-s-p-s-p-p-s-p-s-p-s-p. Each of the primary layers as separated by 2 layers of thin paper and the primary and secondary layers are separated by 2 layers of thicker paper. As modern transformers use plastic film between layers how will changing the material affect the transformers performance, is the thickness important and should I have the transformer vacuum impregnated.
405man said:
As modern transformers use plastic film between layers how will changing the material affect the transformers performance, is the thickness important and should I have the transformer vacuum impregnated.

Having faced a similar dilemma i decided to use as original materials as possible in order to preserve the "sound" of the transformer. The thickness and type of the insulation will have an effect upon the high frequency response and if matching to another channel is important one should use similar paper. Modern wire is in any case better isolated.

I went for a wax dip and no vacuum and did the job myself.
Thanks for the advice, I still have some of the layers to be unwound and I shall check the number of turns again, I have 2 transformers, one from about serial number 18000 and the other about 42000, they look identical.
Though they may still be available from Quad they are very expensive, I had some mains transformers wound at a considerable saving and I have listed the extra ones on eBay from time to time with great success.
I shall be in touch with the transformer manufacturer in the next couple of days to see what insulation material is available, would the main difference be caused by the thickness or the dielectric properties

A few years ago, I wound a few xformers. I used teflon band to isolate the primary layers plus a layer of thin paper. Teflon is a good insulator with low dielectric coefficient (Er=2). Use the gas type as it is thicker than the water type.

For some time, I had this idea of using synthetic flyscreen to separate the layers. IMO it is ideal, since it is more than 50% air, and the thickness of the plastic wire is about 0.3mm. Mmmmh.
I appear to have a problem with my attachment...Stuart


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    output 22.jpg
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Any impregnation will increase capacitance. If it wasn't impregnated before, why impregnate now?

Exactly. vacuum Impregnation with an insulating varnish is the opposite required for reducing the capacitance.......if one has used Kraft paper to reduce it. Why ruin by increasing the dilectric capacitance with impregnation ? An end dip to seal but not fully impregnate output transformers.
Modern day materials & esp winding wire have vastly improved lifetime stabilities, just look how many times transformer wire can be manipulated and bent before insulation breakage occurs ?

By going to parallel push pull with much reduced primary impedances the critical dilectric permittivity becomes less critical (fewer turns) and a larger wire diameter is often used, that impregnation or yellow polyester can be used. I find these creep with time. However those who have designed transformers for true class B stages will soon realise how careful the design has to be, to err the losses.

I have recently had my dad's old Quads rebuilt by Keith Snook, a valve sound magician in Cardiff. He replaced all the dud transformers with new ones wound by Majestic transformers in Poole www.[B]transformers[/B].uk.com/. He repotted them in modern compounds in the original boxes. I guess if you contact him via his website at www.[B]keith[/B]-snook.info/ then I expect he will be able to fill you in on any information you need.