• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EL34 push pull ultra linear transformers for new build

6A3sUMMER

Member
2016-06-07 6:50 am
artosalo,

I agree. That is a good test.
If a transformer does not have enough core laminations versus the primary Amp x Turns, then low frequencies will cause earlier core saturation.

Global Negative Feedback does not fix that . . .
There is no fooling mother nature.
 
How about trying something different? Forget ultralinear, and regulate the screens with a Maida style LM317 regulator. Run the screens 20V or so below the rating. Simple mod. Pete Millett sells a PCB on eBay No personal experience with this board, but he has been selling them for years with good feedback. Recommend using the 1uF 400V film caps for C1 and C2 in the original schematic in LB-47 Fig 1. I use a TV horizontal sweep transistor mounted directly to the chassis as a heat sink.
 
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hbc,

The magnetic core has a limit of how strong the magnetic field can become; at that point any increase of the current in the primary does not cause a corresponding proportionate increase of the magnetic field.

Some 'Boutique' core materials and/or special core materials activate early (like at small current changes). Nice for small signals.
But they also do saturate very early, at lower current levels than more traditional core materials.

When a core material is in saturation, a sine wave current that is applied to the windings, causes the magnetic waveform to look more like a square wave, or at least like a distorted sine wave. Generally the shape of that distorted sine wave looks different on a single ended amplifier, versus a push pull amplifier.

I hope that answers your question.
 

6A3sUMMER

Member
2016-06-07 6:50 am
hbc,

"adding high frequency bias to the output transformer"?

Are you referring to magnetic tape recorder's high frequency bias that effectively "modifies the hysteresis curve" the audio signal rides on?
Are you going to apply it to a power amp output transformer?
That is an interesting idea to get rid of the near zero area of the hysteresis curve.

Some modern signal sources have audio outputs that have some low level clock and other high frequencies out (beyond the audio frequency range).
Those spurious signals might beat with a high frequency bias, and the beat frequency may be in the audio frequency range and be heard as a continuous tone.
Attention to details is needed to prevent that.
 
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