&
2) Does anyone have experience with this and does it really make a big difference in the sound ?

I ask because it seems to me that if you go for low DCR it means getting a unit that will be designed to supply a greater current and that will mean that voltages will run higher .
Recently I bought a 12.6V fil transformer spec'd for a max . of 2.5 Amps . Running it with four tubes drawing a total 1.2A netted a voltage of 13.6 , down only 0.2V from the spec'd 13.8 no load V .
It seems to me that trying to use a big honker on a B+ power supply might be unpredictable , forcing fine tuning with voltage lowering resistors and that's just a waste of power + bad design. Are there any really accurate ways of working this out beforehand ? ( oops, I guess that's three questions. )

Thanks

 butt in w/another question - Sector-7G 18:41:56 10/26/02 (1)
 No downside. - gdahl 21:15:30 10/27/02 (0)
 Thanks for the answers guys , 't helps . (nt) - Ian L. 22:37:54 10/18/02 (0)

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 butt in w/another question - Sector-7G 18:41:56 10/26/02 (1)
 No downside. - gdahl 21:15:30 10/27/02 (0)
 Thanks for the answers guys , 't helps . (nt) - Ian L. 22:37:54 10/18/02 (0)
 Re: Question about Using Low DCR Power Xfrmrs in amp circuits - gdahl 15:12:28 10/17/02 (0)
 Re: Question about Using Low DCR Power Xfrmrs in amp circuits - MQracing 21:53:07 10/16/02 (1)
 Re: Question about Using Low DCR Power Xfrmrs in amp circuits - KevinC 03:33:24 10/17/02 (0)
 Re: Question about Using Low DCR Power Xfrmrs in amp circuits - kevinc 05:21:49 10/13/02 (0)

I'll leave the other questions to others. I've never made a comparison such as is suggested, so I have no practical experience.

Kevin

Hope you don't mind me making a comment on this subject.

RE: low DCR in power tranneys several thoughts come to mind.

1) most DCR measurements your see are of the windings cold and not at operating volts and currents. The "hot" windings can be signficantly higher. And there is not a relationship that the lower the cold DCR then, ipso facto, the lower the HOT DCR will be.

2)the DC resistance of the copper circuit is only one of several IMPEDANCES in a power transformer. By itself, even taking into account point 1 stated above, the DCR of the copper winding could well be (in some designs) the smallest impedance of the transformer overall. The impedance of the core assembly can and does in some designs swamp the loss mechanism of the DCR of the copper circuit.

And these core losses will be present in any trans made on the planet. Thing is a trans with a real, real low copper DCR but built on a junk core could still have a cumulative impedance that is much, much higher than another specimen built on a better core but which has, as an example, a slightly higher DCR in it's copper circuit.

Point is that DCR vastly underdescribes what is important in a power transformer is considered solely and exclusively as a barometer of quality in a power transformer.

MSL

I think that when people suggest looking for a low DCR secondary, they really mean they are looking for a power transformer with low temperature rise and good regulation. As MQRacing so aptly explained, low DCR isn't by itself a measure of quality. A good power transformer is unlikely to have high DCR, but it takes more than low DCR to make a good power tranny!

The true goal, a power supply with low output impedance, is truly worthwhile. If a power transformer has good regulation, the ouput voltage will be close to the nominal value even when there is little or no load. Since it is often hard to find a power transformer with good regulation, sometimes people look instead for a transformer that has excess current capacity and a low-DCR secondary, in order to lower the supply's output impedance. Unless the transformer also has good regulation, the output voltage will be too high. The other unfortunate side effect is too much fluctuation of the output voltage as the load changes.

Gary Dahl

Gary Dahl