The rule to calculate the load impedance of two or more valvces connected in parallel - diyAudio
 The rule to calculate the load impedance of two or more valvces connected in parallel
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 4th February 2004, 03:38 PM #1 diyAudio Member     Join Date: May 2002 Location: Lesina (FG) - Italy The rule to calculate the load impedance of two or more valvces connected in parallel Which is the rule that allows to calculate the load impedance (and so, the impedance of the output transformer) of two or more valves connected in parallel ? Is it possible to connect in parallel two or more valves having a different internal resistance (i.e. 1000 and 2500 ohm) ? ...If so...is the rule the same ? With anticipated thanks.
 4th February 2004, 04:11 PM #2 diyAudio Member   Join Date: Nov 2003 Location: Leeds 1/R = 1/r1 + 1/r2 .... + 1/rn
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Posted by Paul D. Scearce on March 22, 2002 at 10:52:01
In Reply to: Load line posted by Bas Horneman on March 22, 2002 at 03:43:34:

From Ohm's law, impedance is V/I. To add an impedance line to a tubes plot, you need to find two points on the load and draw a straight line through them.
For a resistance coupled tube, start with the B+ voltage. If the plate of the tube is at that voltage, the voltage accross the load resistor is 0. From Ohm's law, current is V/R, in this case 0 ma. So the first point is at B+ v,0 ma. You can than pick any voltage less than B+ to find your second point. Lets pick 0 volts. If 0 volts appears at the plate of the tube, the voltage accross the load is B+ volts. Using Ohm's law again, current is B+/R, and your second point is B+/Rma,0v.

For example say B+ is 200v and the load is 20kohm. Draw one point at 200v,0ma and another at 0v,200/20ma(0v,10ma in other words). Then draw a straight line through these points. That is the load line.

This line passes through the grid voltage lines of the tube, so you can tell what the plate voltage will be for any grid voltage. Bear in mind this is only an approximation, but it should give you a fair idea of how the tube will opperate.

Hope this helps

Paul

Quote:
 Is it possible to connect in parallel two or more valves having a different internal resistance (i.e. 1000 and 2500 ohm) ? ...If so...is the rule the same ?
Don't think it is possible...well it could be done... but won't sound good ...methinks

 5th February 2004, 12:38 PM #4 diyAudio Member     Join Date: May 2002 Location: Lesina (FG) - Italy Thanks to all. However, I think that it is not clear for me. For example, if I want to connect in parallel two triodes (having rp=1200 ohm) + 3 pentodes (having 5400 ohm)...how should I calculate the total impedance (i.e. the useful value for output transformer) ?
 5th February 2004, 12:41 PM #5 diyAudio Member     Join Date: May 2002 Location: The great city of Turnhout, BE Blog Entries: 8 I'm no tube specialist, so not sure on the way to calculate it, BUT I am pretty sure that whatever it is, you aend up with very unequal load sharing by the tubes. If you do this, at least use same tubes to parallel. That way, the total output power can be made the sum of the individual output powers. Jan Didden
 5th February 2004, 03:52 PM #6 diyAudio Member   Join Date: Nov 2003 Location: Leeds Paralleling up a mixture of triodes and pentodes seems a bit odd to me too but I think it should be possible if they are all separately biased. 1/r = 1/1200 + 1/1200 + 1/5400 + 1/5400 + 1/5400 = 0.0022222 r=450 Ohms
 6th February 2004, 12:53 PM #7 diyAudio Member     Join Date: Jan 2004 Location: Scandinavia This could very well be the virge of a scientific breakthrough! Actually I'm not joking. This has probably never been tried. Parallelling pentodes and triodes, what an interesting idea. You only wait, next year we'll see the Audio Note 'Asagohan' amp with 2A3 _and_ KT88!!!
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Hi,

Quote:
 You only wait, next year we'll see the Audio Note 'Asagohan' amp with 2A3 _and_ KT88!!!
It could also be named "Kondo San Nogo"

Cheers,
__________________
Frank

 6th February 2004, 03:17 PM #9 diyAudio Member     Join Date: May 2002 Location: Lesina (FG) - Italy ... The eyes see what the mind knows !
 6th February 2004, 03:36 PM #10 diyAudio Member     Join Date: Jan 2004 Location: Scandinavia Hehe.. nice one there On a more serious note, I realize the difficulties in not just differing plate r, but also the drive requirements of triodes vs pentodes. But my point was, that everybody *knows* it can't be done, so nobody does it. And so there is no progress. One of these days I'm gonna make a lab-amp with 10 spare sockets just for testing these crazy ideas when the urge comes over me... Everybody *knows* that flea-power triodes have too high distorsion to be of any good. But the sound is still to die for.

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