Small Push Pull tube amp build, advice sought.
- deltafred
- Opamp Operator
I used EL84s. As they are out of my spares box and untested I tried 4 different ones with no change in output.
Thanks for the correction on parallel/series, it was bothering me that parallel didn't seem right.
Thanks for the correction on parallel/series, it was bothering me that parallel didn't seem right.
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
- deltafred
- Opamp Operator
Manfred, I got a bit of time on it with the scope.
It's the PI that is clipping not the output stage, it is biased too high so is clipping to the HT. I'm using the one from the 18Watt Lite IIb. When I get some more free time I need to get that sorted out.
It's the PI that is clipping not the output stage, it is biased too high so is clipping to the HT. I'm using the one from the 18Watt Lite IIb. When I get some more free time I need to get that sorted out.
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
- Manfred
- Tube Twister
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Here is the corrected dimensioning.
To reach the Ra of 4.8 kOhm you now have to connect an 8 Ohm speaker to the 15 Ohm tap or a 4 Ohm speaker to the 7.5 Ohm tap.
The maximum output power that can be reached is about 3.4 Watts.
To reach the Ra of 4.8 kOhm you now have to connect an 8 Ohm speaker to the 15 Ohm tap or a 4 Ohm speaker to the 7.5 Ohm tap.
The maximum output power that can be reached is about 3.4 Watts.
Last edited by Manfred on 13 Dec 2020, 16:59, edited 2 times in total.
- Manfred
- Tube Twister
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Hi Deltafred
you had written:
The transformer must supply about 40 watts for the power output stage including heater voltage supply and should be
should have a power value of 50VA for this alone. In addition, there is the power consumption of the preamplifier and the phase inverter.
What is the power rating of your transformer?
If your transformer has a smaller power value,
then you could make the power of the output stage less.
It is a disadvantage of the class A power amplifier that the current consumption in idle mode is high.
you had written:
With the new circuit, the current consumption is higher with the new quiescent current setting.The MT was just warm to the touch after about 30 minutes at full power (5W), the OT still felt cold.
The transformer must supply about 40 watts for the power output stage including heater voltage supply and should be
should have a power value of 50VA for this alone. In addition, there is the power consumption of the preamplifier and the phase inverter.
What is the power rating of your transformer?
If your transformer has a smaller power value,
then you could make the power of the output stage less.
It is a disadvantage of the class A power amplifier that the current consumption in idle mode is high.
- Manfred
- Tube Twister
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I made a mistake in the output power calculation.
I took (Ua~_peak * Ia~_peak) / sqrt(2) this is wrong, corredt is Ua~peak/sqrt(2) * Ia~_peak) / sqrt(2) = (Ua~peak* Ia~_peak)/2.
So the output power is about 1.7 watts per tube so 3.4 watts total.
I have corrected the diagram above accordingly.
I took (Ua~_peak * Ia~_peak) / sqrt(2) this is wrong, corredt is Ua~peak/sqrt(2) * Ia~_peak) / sqrt(2) = (Ua~peak* Ia~_peak)/2.
So the output power is about 1.7 watts per tube so 3.4 watts total.
I have corrected the diagram above accordingly.
- Manfred
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Here the Class B version provides more output power without quiescent current.
If the transformer has a 12.6 VAC winding for the heating filament, you can generate the bias voltage by means of a double-wave rectification.
If the transformer has a 12.6 VAC winding for the heating filament, you can generate the bias voltage by means of a double-wave rectification.
Last edited by Manfred on 14 Dec 2020, 22:33, edited 1 time in total.
- deltafred
- Opamp Operator
Thanks for all this design work Manfred, it is really appreciated.
I can generate a -22v bias voltage easily with a separate small transformer, I have lots to choose from and am sure I can find one suitable.
I haven't got back to it yet as other jobs keep getting in the way.
I can generate a -22v bias voltage easily with a separate small transformer, I have lots to choose from and am sure I can find one suitable.
I haven't got back to it yet as other jobs keep getting in the way.
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
- Manfred
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In the circuit diagram I had entered the bias voltage value with -22VDC instead of -20VDC I have corrected the circuit diagram above.
You can also generate the bias voltage from the high voltage winding.
You can also generate the bias voltage from the high voltage winding.
- deltafred
- Opamp Operator
No progress has been made on the amp, I see it every time I go in my store cupboard and it reminds me that one day I will have to get back to it.
I've just had a PM for info on Partridge transformers so am posting what I have in case anyone else needs it.
I've just had a PM for info on Partridge transformers so am posting what I have in case anyone else needs it.
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012