PSU id and help (psu designer ii)

[surfstu]

I have a transformer from an old heathkit s99, I presume it is approx 200ma but I'm not sure. I've attached a schematic for the circuit it came from. It was powering 4ecl86 and 3 ecc83's and 2 ef86's.

I have no idea of what values to enter into duncans psu designer, is the RMS V = 270 x 1.414 = 381V - and then how do I calculate the source resistance?

Is there a way to calculate more info from this transformer seeing as on the full scematic

HT 1 = 320V
HT 2 = 270V
HT 3 = 250V

cheers Stuart

 

[DUG]

"I have no idea of what values to enter into duncans psu designer, is the RMS V = 270 x 1.414 = 381V - and then how do I calculate the source resistance?"

look at the data sheet for V10: GZ34

http://www.wooaudio.com/docs/tube_data/5AR4.pdf

Hope that helps.

 

[DF96]

RMS voltage is 270V. Peak will be 381V. I believe PSUD2 uses RMS, so enter 270V. For source resistance measure primary and secondary resistance with a DVM, and then enter the results into the PSUD2 transformer calculator (or do the calculation yourself).

 

[surfstu]

Thanks Df96, I didn't realise I could just stick a DVM on primary winding (mains side?) and then over the secondary winding (leave CT out?) to get resistances - that I could then apply to a formula to find the source resistance!

If I then setup a circuit in PSUD2, using full wave rectifier (GZ34) followed by CRCRC will I be able to identify the current throught the circuit by seeing what flows through the final 5K resistor that PSUD2 puts in by default?

Or do I change that final 'resistor to ground' to a resistance that matchs the perceived resistance of the amp I wish to build?

If I wish to build the original Baby Huey amp that gingertubes modded for UL operation, should I be changing the value of the final 5k resistor of PSUD2?

Thanks again for everyones help here, and thanks Dug for the data sheet

 

[DF96]

I'm not sure about the CT, as I can't remember what PSUD2 assumes for secondary resistance.

You can use either a resistor or constant current load for your PSU. A resistor may better approximate the load of a real valve amplifier. Set it to whatever value is appropriate.

 

[surfstu]

Thanks DF, but how do I know what value is appropriate for the final R in PSUD2

and... I just read somewhere that the primary resistance is taken across the mains, and the secondary is HALF the secondary... I'm guessing this means CT to one side of the secondary?

 

[surfstu]

If this is the circuit I intend to build then is there a way of approximating the final R value?

 

[surfstu]

better image!

 

[DF96]

Find the current, then use Ohm's Law.

 

[surfstu]

Would it be safe to say that the current drawn by this circuit (4 x ecl86) will be 4 x 35mA which is 140mA?

 

[DF96]

That may be a reasonable estimate. You can calculate quiescent current by using Ohm's Law on the cathode resistors. A typical push-pull Class A output will increase its current draw by 10-20% at full output, but that will only be on music peaks so can almost be ignored. Class B will increase more, of course.

A design should say what current it draws. The designer must know, because it is part of the design process.

 

[kstagger]

with PSUD2, instead of an end resistor, you can use a constant current load. It's much handier than a final resistor - especially if you really do know what the "average" mA will be. Obviously easier with a Class A circuit.

 

[surfstu]

Great guys thanks...

So for the circuit posted below I can assume that V across the cathode of final stage is 10.5 V and the cathode R is 390ohms...

Therefore I = 10.5 / 390 = 0.0269 or 27mA

This is the idle current which would be the same as the quiessent current seeing as this amp operates mainly in class A (is this correct?)

and.... I,m still trying to figure out how the first stage only draws around 1mA and has a constant current source to determine this...

my limited background in physics always taught me that the current was the same for the entire circuit?

 

[surfstu]

Source resistance calculated 1

Ok, thanks to all here - I'm making headway!

primary resistance = 9ohms

secondary resistance = 63ohms (CT to Sec)


Source resistance = (primary resistance / (Vpri/Vsec)2) + Secondary resistance

Vpri = 230
Vsec = 270

(Vpri/Vsec)2 = 0.726

therefore Source resistance = 75.3ohms