Musical Machine (triode PP EL34) question(s)
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tinitus
diyAudio Moderator R.I.P.

Join Date: Nov 2005
I was tought to do it like this
something to do with safety
that is, if I have drawn it ok
Attached Images
 NGV bias.png (18.6 KB, 265 views)

mr2racer
diyAudio Member

Join Date: Jul 2009
Correction

Thanks Tinitus,

I think it amounts to the same thing. Two voltage dividers in parallel. One variable and the other set. I think I have it right nowThe lower set divider, 37/22k divider yields 24.6 volts. The adjustable divider, 27/10/22k yields between 24.6 and 35.8 volts. Which makes gives the same range of adjustment as the original design. But if the wiper fails the minimum bias voltage becomes 24.6, the set divider output.
Attached Images
 bias 2.GIF (5.2 KB, 262 views)

Last edited by mr2racer; 17th February 2013 at 07:08 PM.

 18th February 2013, 11:24 PM #33 mr2racer   diyAudio Member     Join Date: Jul 2009 Hey All, I was looking at Poindexters schematic just now and he labels the plate as 6. From my information the plate is 5. And 6 is not connected? Is this a typo? Last edited by mr2racer; 18th February 2013 at 11:30 PM.
boywonder
diyAudio Member

Join Date: Jan 2008
Location: So.Cal.
Quote:
 Originally Posted by mr2racer Hey All, I was looking at Poindexters schematic just now and he labels the plate as 6. From my information the plate is 5. And 6 is not connected? Is this a typo?
Assuming that you are talking about the 6GK5, you are correct; the plate is pin 5. On the Poinz schemo I have, he has the upper 6GK5 plate labeled as 5 and the lower 6GK5 labeled as 6........a typo.

 19th February 2013, 01:49 AM #35 mr2racer   diyAudio Member     Join Date: Jul 2009 Thanks, I thought so. On mine the upper is hard to read and the lower is clearly a six. I'm building some boards and needed to know for sure.
mr2racer
diyAudio Member

Join Date: Jul 2009
CCS

Hey All,

I'm trying to understand how a constant current source functions using load lines. I'm assuming that if current is set, in this case at 8ma per tube. And maximum input is .785 volts in either direction, centered at .5 volts. The voltage swing would be about 78 volts with maximum output of .92 watts and 115 volts @8ma.

Math is not my strong point. But do these calculations seem accurate? I've included a graph that I hope shows what I'm thinking.
Attached Images
 6gk5-poindexter.JPG (74.4 KB, 186 views)

scott17
diyAudio Member

Join Date: Aug 2009
Do you mean .785V/2? If you mean .785 + and - then you will go beyond the 0V grid. Maybe -1V is a better bias point?

Quote:
 Originally Posted by mr2racer Hey All, I'm trying to understand how a constant current source functions using load lines. I'm assuming that if current is set, in this case at 8ma per tube. And maximum input is .785 volts in either direction, centered at .5 volts. The voltage swing would be about 78 volts with maximum output of .92 watts and 115 volts @8ma. Math is not my strong point. But do these calculations seem accurate? I've included a graph that I hope shows what I'm thinking.

Last edited by scott17; 21st February 2013 at 02:03 AM.

 21st February 2013, 10:18 AM #38 mr2racer   diyAudio Member     Join Date: Jul 2009 So you can still set the bias point? I guess you would still be able to by doing the calculation for the cathode resistor. The ma doesn't change much but the voltage does. So if the input voltage maxes out at .785 the input range is between 0 and .785? Not +.785 and -.785?
scott17
diyAudio Member

Join Date: Aug 2009
Quote:
 Originally Posted by mr2racer So you can still set the bias point? I guess you would still be able to by doing the calculation for the cathode resistor. The ma doesn't change much but the voltage does. So if the input voltage maxes out at .785 the input range is between 0 and .785? Not +.785 and -.785?
I found the 6GK5/EL34 schematic using the 10M45S for the LTP CCS. I should have read through the thread and actually knew what I was commenting on, before I commented about the bias.

It appears that the input voltage would be 0.785V P-P.

Last edited by scott17; 21st February 2013 at 02:37 PM.

 21st February 2013, 05:41 PM #40 boywonder   diyAudio Member     Join Date: Jan 2008 Location: So.Cal. Kevin: Your revised bias schemo in post # 32 doesn't help when the pot wiper goes open, it just burns more current from the bias circuit from the additional resistors in parallel. Take another look at the schematic I posted in post #29; the extra R divider chain connects to the grids.

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