74' Dagnall Power Transformer: Rewind Specs & Flux Band Noise Reduction?

[jgab]

Hi,

I have been reading about the Power Transformer Copper Flux Bands, like the one in the photo below.



My question is: why do some Power Transformers have them and some don't? I noticed a couple of my Dagnall Power Transformers from the 70's have them but my Drakes from the 80's don't. I also noticed Chris Merren makes transformers with the copper flux band, but Brian Wallace, Heyboer, Hammond, Mercury and most others don't.

Have any of you installed them and did it make a difference in noise reduction? Am I safe to assume it is not need?

Thanks,
J

 

[Pete Farrington]

@william vogel ?

 

[william vogel]

I’ve put them on transformers and I’ve left them off but I’ve never A/B tested identical winds to be able to tell you. I put them in place because what I wound used them originally and did it for the original look and design same as Merrin. My amps are quiet but I don’t credit it to the flux band.

 

[Pete Farrington]

I put them in place because what I wound used them originally

Any idea what they're supposed to do, how they're supposed to work?

 

[playloud]

Any idea what they're supposed to do, how they're supposed to work?

My understanding is that they're in that plane to mitigate leakage flux. The laydown type have a copper shield wrapped around the windings (same principle).

 

[william vogel]

Any idea what they're supposed to do, how they're supposed to work?

They operate as a shorted winding of a single turn and of course on the outside of the lamination stack and the fact that it’s a shorted turn, it collapses the magnetic field in close proximity to the turn. It definitely can’t collapse all the magnetic flux lines radiating out of the transformer but it does make quite a difference.

 

[jgab]

Ok thanks. Brian Wallace recommended that Heyboer rewind my 74' Dagnall Power Transformer, so I am going to go with them.

Here are their specs Heyboer plan to rewind my transformer. I think there is an error on the bias secondary spec. One of the bias secondaries should be 0 volts right?:


Is 180vac/180vac on the high voltage secondary's a good spec? I also see 175VAC from some aftermarket PT's. I am hoping to get about 470 vdc on my EL34 plates.

I know tube current draw, tube bias, OT, etc. effect the 470 vdc I am trying to get on my EL34's, but will a 180vac/180vac from my Power Transformer get me close?

What do some of your power transformer high voltages secondary's measure?

Thanks,
J

 

[TAZIN]

A secondary voltage of 180-0-180 should be close to delivering a rectified voltage of 470v. It could produce a tad higher voltage depending how much the output valves draw for bias. It seems the general consensus is roughly 175-0-175 for approx. 470vdc.
Yes, one of the Blue bias wires should be labeled 0v.

 

[jgab]

Sounds good Heyboer said they can wind the secondary to give me 175-0-175 with 120vac on the primary.

Looking forward to it.