He said one the previous page that a single 115v winding is possible. I was after a dual 115v, so i could use it here (in Florida 115v) and when i get back home (England 230v).
the dual 115v would satisfy us both. In parallel for 115v, and in series for 230v.
His last post only spoke of only 230V.
JD
His last post only spoke of only 230V.
JD
Indeed, however i already asked for dual 115v. He said no, only single, that's what i was trying to say. 😉.
See post 702 & 703
http://www.diyaudio.com/forums/grou...ndrea-ciuffoli-group-buys-71.html#post2086254
However i guess it would be possible for dual 115v if there was sufficient demand.😱
Can someone explain to Tube Noob what caps and resistors do in tube cathodes? Is that 3.8V marked in the schematic bias voltage?
Hi Jeffrey, Gerd told me that it is a problem to build this with 2 x 115V
because of the winding layers and the wires go out.
But it is no problem to build this as 1 x 115V or 1 x 230V only.
Michael
because of the winding layers and the wires go out.
But it is no problem to build this as 1 x 115V or 1 x 230V only.
Michael
Will "normal" heatsink with 1"/25.4mm solder tap spacing fit Salas IRFPs? Those have 23-24mm spacing, which isn't that common?
I found the same issue. That's a design error on the PCB unfortunately. The footprint is not also centered. The solution is to rip a pin off the heatsink and solder only one that will center the IRFP. I would not mess around enlarging the hole for both.
The resistor in the cathode makes the grid voltage negtive vs the cathode. The grid is connected to ground through the leakage resistors 2x470K. As you need to supply negative voltage to the grid to control the current through the space charge you can do by making the cathode slight positive or supply negative voltage to he grid and ground the cathode. In anyway there must be a negative voltage between grid and cathode or the tube will "short". The capacitor stabilizes the bias as the current changes through the tube also the bias would change. The cap in other words increases the gain of the tube.
OK, I would recommend for the capacitor use 220uF 16V Oscon or Elna Silmic II. I vote for the Silmic II but it's up to your personal taste. Yes the cap is low voltage 16V.
Calculation is very easy: B+ is 270V, plate voltage is 90V. Voltage drop accross R1+R2+R3+R4= 180V. The current for 1 tube (2 units) is 180/(47000/4)= ~15mA -> 7.5mA through each unit of one tube. Now the voltage drop on R5 or R6 or R17 or R18 is 470*0.0075= ~3.5V which is the self bias of the tube. If you have a look the tube chart you will see is very close.
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I would like to say that's an easy and expensive solution that could compromise performance. Return signal from different kind of loads (heater, digital, analog etc.) to the source (separate windings) can still jam each other because they all share the same transformer's core. Separate transformers is always an improvement (but less convenient to wire). In this case a stock R-core transformer for heater and B+ cost $30 and you would need to spend only another $30 for two standard 10va 9+9V transformers for D5+ and A+-5.
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........The cap in other words increases the gain of the tube. Actually in case of the self bias method the cap "maintains" the gain by holding bias voltage closer to constant (in AC). Without the cap the bias voltage would be modulated against the signal, resulting in loss of gain.
In fixed bias the cathode can be grounded. Self bias is the safest method. The fixed bias is more dangerous. If the device supplying negative voltage fails you would see in some cases the tube overloading going to full conduction, the cathode becomes red, the glass will melt and the tube will implode. I hope this will not become a new sport on YouTube like those showing woofers burnouts.
Sorry for the basic explanation, I hope it helps.
In fixed bias the cathode can be grounded. Self bias is the safest method. The fixed bias is more dangerous. If the device supplying negative voltage fails you would see in some cases the tube overloading going to full conduction, the cathode becomes red, the glass will melt and the tube will implode. I hope this will not become a new sport on YouTube like those showing woofers burnouts.
Sorry for the basic explanation, I hope it helps.
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Will these R-Core transformers be OK to use?
R80-36 260-230-0-230-260(90mA). 2.5-0-2.5(3A).(3.15-0-3.15)X2(3A)
100W R-Core Transformer 115V//230V ,Pre amplifier / DAC bei eBay.de: Transformers (endet 02.03.10 00:24:25 MEZ)
and
R26-29 0-9 X3(1.1A),9-0-9(1.1A)
50W R Core Transformer,115V//230V, for Preamp,DAC/R26-x bei eBay.de: Transformers (endet 11.03.10 01:01:21 MEZ)
Thanks
R80-36 260-230-0-230-260(90mA). 2.5-0-2.5(3A).(3.15-0-3.15)X2(3A)
100W R-Core Transformer 115V//230V ,Pre amplifier / DAC bei eBay.de: Transformers (endet 02.03.10 00:24:25 MEZ)
and
R26-29 0-9 X3(1.1A),9-0-9(1.1A)
50W R Core Transformer,115V//230V, for Preamp,DAC/R26-x bei eBay.de: Transformers (endet 11.03.10 01:01:21 MEZ)
Thanks
No, I missed that post. Thank you very much for pointing me in the right direction.
Is R3/270k little smallish (in size) in the High Voltage Power Supply? P = V²/R = (350V(?))²/270kohm = ~0.45W so 0.5W is too small, 1W minimum? I can't find any ~8mm long 1W 270k resistor..
So it needs to be at least 1W? Minimum 5pcs, I think I missed it because of that. Thanks. 🙂
Yes, for a matter of power dissipation AND voltage ratings of the resistor.
For example some 1/2 Watt resistor would not handle 350V drop across and they short. You would need two in serial at least.
Those are fine I just received from DIYclub.biz . You obtain AC for the heater rail from 2.5+2.5+3.15.
Yes, please post your codes and where you have ordered parts for the other boards also. It's much appreciated.
Thank you very much.
Thanks, so that Vishay/BC mentioned by Ferrari isn't enough, just 350V. I will go for a bigger one and drill a hole for it. 🙂
Maybe Little Demon will do
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