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jdef 2nd March 2012 11:01 PM

valve/tube output transformer construction
 
Hi,

I am thinking of winding a pair of output transformers for an EL34 PP based circuit. I have looked at the Williamson transformer design details and also gone through the Radio Designers Handbook (ed4) and roughly worked out turns ratio, core size etc., but I am interested in knowing more before constructing a coil winding machine to help with the process. Firstly, the Williamson amplifier uses two bobbins with one put on the other way to make the windings symmetrical yet I see few commercial amplifiers employing this method; so is it necessary and if so what sonic advantages does it give ?

Also, the RDH refers to electrostatic shielding between sectionalised primaries and secondaries. Is this between every boundary between the primary and secondary windings, and what form does it take, a brass shim; or would an aluminium one do ? What's the purpose of these, is it to reduce the effect of winding capacitances, and again, are they used in commercial transformers ?

Any information or insight would be very much appreciated.

Yours,

Jolyon

AJT 2nd March 2012 11:09 PM

lots of threads here on the topic, please seek out posts by BudP, cerrem, YvesM and smoking-amps......

aardvarkash10 2nd March 2012 11:37 PM

spend a few hours on Patrick Turner's site too - near-impenetrable theory stuff, but worth it

AJT 2nd March 2012 11:41 PM

yes, Patrick Turner is a good read indeed......

jdef 3rd March 2012 12:00 AM

Thanks everyone, just been looking. Very valuable stuff there. I'll need some time to take it in !

Yrs,

J.

Eli Duttman 3rd March 2012 02:39 AM

J.

Williamson style topology requires O/P "iron" of the VERY best quality. Otherwise, the phase shifts in the circuitry will eat you alive. I suggest you consider Mullard style circuitry, as it is less problematic in the stability dept.

jdef 3rd March 2012 01:18 PM

Hi Eli,

I was going to use the Lowther LL26 circuit as the basis for my amplifier and am planning on using c cores for the op transformers. I just mentioned the Williamson cct as it came with reasonable detail on transformer construction. However, no mention is made of electrostatic shielding in the Williamson op tx.

Yrs,

Jolly

LinuksGuru 3rd March 2012 01:46 PM

Audio transformers have NO electrostatic shields !

Yvesm 3rd March 2012 02:31 PM

Quote:

Originally Posted by jdef (Post 2930925)
Hi,
. . .
Firstly, the Williamson amplifier uses two bobbins with one put on the other way to make the windings symmetrical yet I see few commercial amplifiers employing this method; so is it necessary and if so what sonic advantages does it give ?

Using two bobbins is not necessarly used to make windings symmetric but it's a mean to reduce the end to end capacitance of a winding.
RDH4 uses the term of "vertical sectionizing". Browse for that, but this not the only way.
End to end capacitance of windings are responsible for peaks of resonance at high frequencies and should be avoided at less than, say, 50Khz, that is 2 or 3 octaves above the usual 20Khz limit in order to do not produce excessive in band phase shift.
Quote:

Also, the RDH refers to electrostatic shielding between sectionalised primaries and secondaries. Is this between every boundary between the primary and secondary windings, and what form does it take, a brass shim; or would an aluminium one do ? What's the purpose of these, is it to reduce the effect of winding capacitances, and again, are they used in commercial transformers ?
In output transformers, impedance ratio is usually large enough to allow looking at the secondaries as being at (or near) the ground potential for the primaries.
Browse RDH4's chapter 5 again, and again and again . . . :D

Yves.

jdef 3rd March 2012 04:41 PM

Thank you all; it's great to be able to discuss this with people who know and are willing to share their knowledge.

Yrs,

Jolyon.


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