Output transformer spec help

[Flipmoore]

I am wanting to order two output transformers from electraprint. But not sure if I am giving them the correct data. Running el34 push pull ul, fixed bias at 40mA, B+ 450v

For electraprint
105w
4.6k plate to plate
100mA/100mA
50%ul taps
Load impedance 8 ohm

Would this be accurate?

 

[Steve Morley]

Usually UL taps are between 20% and 43%. Do you have a schematic?

S.

 

[Brinkman]

105W seems very high. Electra-Print has very honest power ratings; a 25W rating will mean -1dB at 29Hz and 30kHz before the onset of core saturation. Edcor is another story…

 

[grovergardner]

Do you need 100 watts? With Electraprint I think 60 watts would suffice. UL taps would traditionally be at 43%, but personally I like them at 50%, sounds more triode-like.

 

[wg_ski]

Yes, that supply voltage and impedance look more like a 50 to 60 watt amplifier, not 105.

 

[Flipmoore]

You gentlemen are correct. My error. It is a 50-60 watt amp. Give me a second and I’ll draw up a schematic

 

[Flipmoore]

Apologize for the rough sketch, it’s been a long day

 

[Brinkman]

Ask Jack about his new enhanced A3 Iso-Linear circuit for use with EL34 tubes. It uses the same 50% screen taps you’re asking for.

 

[6A3sUMMER]

True Ultra Linear mode has a certain characteristic of a reduction in the level of the 2nd harmonic and/or the 3rd harmonic distortion(s). The curve has a dip in the distortion levels, and goes back somewhat on either side of the dip.
But these nulls are not only dependent on the UL Tap percentage %, they require a certain plate to plate impedance to make the null appear at a particular point.

Since many loudspeakers do not have constant impedance across the whole audio frequency band, I would not worry too much about the exact numbers.

Since some want to experiment with output tubes in pentode/beam power mode, Ultra Linear mode, and Triode wired mode, here is a generalization of the circuit modes:
Pentode/beam power mode: UL tap is at 0%.
Triode wired mode: UL tap is at 100%.
Taps that are >> 0% and << 100% are sort of Ultra Linear.

Have fun designing and building your push pull ultra linear EL34 pentode amplifier.
Then enjoy listening.

Tube rolling?
Plug in a pair of KT77 beam power tubes, re-adjust the bias for the same current as the EL34s were at, and then listen some more.

I have only used 40% UL taps on my UL push pull amplifiers (the only UL tap % on the UL transformers I have)
I have used 20%, 50%, and 80% UL taps on my UL single ended amplifiers.

 

[jcalvarez]

EICO HF-87 and HF-89 are quite simple and easy to build, EL34 UL, 50W.

 

[tjerneld]

True Ultra Linear mode has a certain characteristic of a reduction in the level of the 2nd harmonic and/or the 3rd harmonic distortion(s). The curve has a dip in the distortion levels, and goes back somewhat on either side of the dip.
But these nulls are not only dependent on the UL Tap percentage %, they require a certain plate to plate impedance to make the null appear at a particular point.

Since many loudspeakers do not have constant impedance across the whole audio frequency band, I would not worry too much about the exact numbers.

Since some want to experiment with output tubes in pentode/beam power mode, Ultra Linear mode, and Triode wired mode, here is a generalization of the circuit modes:
Pentode/beam power mode: UL tap is at 0%.
Triode wired mode: UL tap is at 100%.
Taps that are >> 0% and << 100% are sort of Ultra Linear.

Have fun designing and building your push pull ultra linear EL34 pentode amplifier.
Then enjoy listening.

Tube rolling?
Plug in a pair of KT77 beam power tubes, re-adjust the bias for the same current as the EL34s were at, and then listen some more.

I have only used 40% UL taps on my UL push pull amplifiers (the only UL tap % on the UL transformers I have)
I have used 20%, 50%, and 80% UL taps on my UL single ended amplifiers.

In a Single-end amplifier second harmonic has a dip.
In a Push-Pull amplifier second harmonic is 0 % (with matched power tubes), 3rd harmonic has no dip.

 

[tjerneld]

Look at the Push-Pull EL-34 amp with 50% UL-taps in Elektor-2003-04.pdf