Yes, you are right 😱 Thanks
I've found a 175VA
Triad magnetics:
VPS230-760 Triad Magnetics Power Transformers
Or Hammond:
185G230 Hammond Manufacturing Power Transformers
I've found a 175VA
Triad magnetics:
VPS230-760 Triad Magnetics Power Transformers
Or Hammond:
185G230 Hammond Manufacturing Power Transformers
I have made a draw in Visio:
Anyone knows what is the function of the 12k resistor and the 220k condenser at the triode anode? That was not included at the original schematic from the manufacturer, it looks that someone made that modification.
An externally hosted image should be here but it was not working when we last tested it.
Anyone knows what is the function of the 12k resistor and the 220k condenser at the triode anode? That was not included at the original schematic from the manufacturer, it looks that someone made that modification.
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ΟK , in this schematic it looks more complicated than it really is. So first imagine the 220n terminating to the other end of the 220K resistor. This is the feedback compensation, to limit the high freq response in order to make THIS "pole" the lowest high-frequency (dominant) pole in the system (and not the output transformer high frequency cutoff). So the amplifier remains stable. Refer to The Willamson Amplifier analysis (plenty floating around)
The G2 voltage tap is incidental, (any AC is shunted by the electrolytic cap there). The designer just saved a resistor and a capacitor to ground by doing this.
The G2 voltage tap is incidental, (any AC is shunted by the electrolytic cap there). The designer just saved a resistor and a capacitor to ground by doing this.
What is your opinion of this schematic?
I will appreciate any advice. I am a HVAC engineer, not expert in electronic circuits. Tube DIY is just my trial-and-error hobby, “frankensteining” ideas from different schematics and the great collaborations at this forum 🙂 Thank You, Thank You!!
I am wondering how it will sound with the absence of Negative Feedback.
If I run the simulation with the Duncan Amps PSU, it gives me a warning: “The rectifier IFSM (forward current surge maximum) of 1.80A has been exceeded with a value of 1,82A, at time 0.001325S” What can that be? I have frankensteined the PSU from this Mullard Amplifier: Three Watt Economcal Stereophonic Amplifier
I still have not started because I am waiting for the construction of the PS transformer. I have ordered 280-0-280 100mA and 0-6.3V 2.5A. I guess that it will be enough for the two ECL86 and one EZ81
An externally hosted image should be here but it was not working when we last tested it.
I will appreciate any advice. I am a HVAC engineer, not expert in electronic circuits. Tube DIY is just my trial-and-error hobby, “frankensteining” ideas from different schematics and the great collaborations at this forum 🙂 Thank You, Thank You!!
I am wondering how it will sound with the absence of Negative Feedback.
If I run the simulation with the Duncan Amps PSU, it gives me a warning: “The rectifier IFSM (forward current surge maximum) of 1.80A has been exceeded with a value of 1,82A, at time 0.001325S” What can that be? I have frankensteined the PSU from this Mullard Amplifier: Three Watt Economcal Stereophonic Amplifier
I still have not started because I am waiting for the construction of the PS transformer. I have ordered 280-0-280 100mA and 0-6.3V 2.5A. I guess that it will be enough for the two ECL86 and one EZ81
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PSUD II is telling you that the inrush current as the two power supply caps "fill up" exceeds the rating of the rectifier.
There are several ways to overcome this, but first, check to see whether you have "soft start" selected as an option in your simulation. This models the behaviour of a rectifier tube starting from cold. From cold, the tube doesn't fully conduct - it slowy gets lower forward resistance as the heater warms. This automatically overcomes the inrush current problem, but for sim purposes you have to let PSUD II know about it....
There are several ways to overcome this, but first, check to see whether you have "soft start" selected as an option in your simulation. This models the behaviour of a rectifier tube starting from cold. From cold, the tube doesn't fully conduct - it slowy gets lower forward resistance as the heater warms. This automatically overcomes the inrush current problem, but for sim purposes you have to let PSUD II know about it....
I have found a company in Bangkok that is building the PS transformer for me: SACThailand. Their Silk OT's look good. I will use them on my next 300B or 2A3 project.
In the meantime, I am having fun with the bitmap symbols from the Tube Pad Library
In the meantime, I am having fun with the bitmap symbols from the Tube Pad Library
An externally hosted image should be here but it was not working when we last tested it.
Not so quick, but quite dirty so far. The tranny is huge. Almost finished.
This is the latest schematic. Some choices are based in components that I had on the drawer rather than in maths. Please, let me know if you see someting strange 😱
An externally hosted image should be here but it was not working when we last tested it.
This is the latest schematic. Some choices are based in components that I had on the drawer rather than in maths. Please, let me know if you see someting strange 😱
An externally hosted image should be here but it was not working when we last tested it.
G'day, has there been any further progress with this build. Very interested in build it, and the component layout drawing make it so much easier to reference the schematic especially for someone like me who has a little trouble decifering schematics.
Cheers
Cheers
Hi Whiting. Still experimenting.
Today I have connected everything, exactly as in the schematic above, and I am surprised to read +340V at B+ !!! I have disconnected it inmediately
The transformer is correctly supplying 280-0-280 AC, and the rectifier tube is connected as indicated (DC from pin 3, AC to 1-7, center tap to ground). What could be wrong?
Today I have connected everything, exactly as in the schematic above, and I am surprised to read +340V at B+ !!! I have disconnected it inmediately
The transformer is correctly supplying 280-0-280 AC, and the rectifier tube is connected as indicated (DC from pin 3, AC to 1-7, center tap to ground). What could be wrong?
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Yes, with the 3 tubes in. Everything connected, and a 4,7 Ohm speaker dummy loads. And the heaters of the 3 tubes are lighting normally
That actually sounds like about the voltage you'd expect... I could easily have believed higher.
All good fortune,
Chris
Of Course!!! That is what I read on Duncan Amps PSU 2 months ago... How can I be such a chicken? My dumbness is getting worst with old age
I have connected the speakers and it is working!!!!!
The dummy speaker load was not working (open circuit). I have connected the real 4 Ohms speakers, and this are the actual readings:
- B+: 244V
- Pentode cathode: 231V
- Pentode anode: 6.2V
- Triode cathode: 123V
- Triode anode: 1.1 V
When I raise the pot volue up there is a nasty sound, like it enters in oscillation with multiple frequencies. Perhap it needs a grid-stopper resistor at the input but, after the obtuseness that I have experienced today, I will take the DIY day off and I will continue tomorrow
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