GU-50 PP + 10k:16-8-4 Ohm ,20w OPT..what is the best to do? - Page 2 - diyAudio
 GU-50 PP + 10k:16-8-4 Ohm ,20w OPT..what is the best to do?
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 16th January 2013, 06:39 AM #11 diyAudio Member     Join Date: Sep 2006 Location: Pleasant Hill, CA On such low B+ you have to drive it in AB2, look at curves, otherwise output power is limited by saturation. __________________ The Devil is not so terrible as his math model is!
diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by Junm I've tried plotting the loadlines for GU-50 PP triode for B+=400v and Ia at 60mA. I also do calculations based on Turner Audio computation and assumption and i came up with the attached. I just wandering why is it that the AB1 power is lower than Class A power...Does it mean that the tube is only a PP class A? or Am I doing the correct calculations and plotting? any comments please?
is it just my eyes or you mixed up the A point with the AB point?
AB has a little more swing, as I see it, so a little bit more power

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Join Date: Dec 2008
Location: Dau
Quote:
 Originally Posted by Wavebourn On such low B+ you have to drive it in AB2, look at curves, otherwise output power is limited by saturation.
Thanks,

What particular curves I will refer to? I'm just learning to look the curves and a little bit confused.

So 400v B+ in triode is too low? does the b+ reffered to is the B+ from PSU or the one measured on the GU-50 Plate?

I will try B+ 450v and see what it takes...

diyAudio Moderator

Join Date: Jan 2011
Location: In Transient
Quote:
 Originally Posted by Junm Thanks, What particular curves I will refer to? I'm just learning to look the curves and a little bit confused. So 400v B+ in triode is too low? does the b+ reffered to is the B+ from PSU or the one measured on the GU-50 Plate? I will try B+ 450v and see what it takes...
B+ refers to the supply voltage, for triode you can use the chart on the lower right corner - but you alrady have one - the one that you posted earlier is a triode chart. IMO, GU50 is not the ideal candidate for your PT and OPT combo.

Jaz

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Join Date: May 2003
Location: Palatiw, Pasig City
Quote:
 Originally Posted by Junm I'm a little bit confused on plotting loadline for GU-50 triode mode. can somebody help me draw loadline for 10k load and 450v B+..TIA
there is a good explanation found on RCA tube manuals, can be downloaded at Pete Millete's site.....Tube Data
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....

diyAudio Moderator

Join Date: May 2003
Location: Palatiw, Pasig City
Quote:
 Originally Posted by Junm I've tried plotting the loadlines for GU-50 PP triode for B+=400v and Ia at 60mA. I also do calculations based on Turner Audio computation and assumption and i came up with the attached. I just wandering why is it that the AB1 power is lower than Class A power...Does it mean that the tube is only a PP class A? or Am I doing the correct calculations and plotting? any comments please?
at idle you are running your tubes at 24watts or 48watts total and you are in classA region, not a bad thing...not much of a concern....

your grid bias of -70volts will require more from your drivers.....i am curious how you will supply the needed drive....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....

 16th January 2013, 04:26 PM #17 diyAudio Member     Join Date: Sep 2006 Location: Pleasant Hill, CA Right, saturation of driver is one more thing that can cause such limitations, except saturation of output tubes. It can supply enough swing for class A (lover bias voltage, lower swing required), but saturate on lower swing than is needed for class AB (higher bias, and higher swing is needed). Since transconductance of output tubes is higher on higher current, you are getting more power from the same output from driver. __________________ The Devil is not so terrible as his math model is!
diyAudio Moderator

Join Date: Jan 2011
Location: In Transient
Quote:
 Originally Posted by Junm I've tried plotting the loadlines for GU-50 PP triode for B+=400v and Ia at 60mA. I also do calculations based on Turner Audio computation and assumption and i came up with the attached. I just wandering why is it that the AB1 power is lower than Class A power...Does it mean that the tube is only a PP class A? or Am I doing the correct calculations and plotting? any comments please?
I don't think the load line for Class A is correct, at least not with B+ of 400V... See if the below makes sense, I also changed the bias point a bit, hope I got it right...

For Class AB1
Class B Calculation
===
Irms = 0.115 / SQRT(2) = 0.081
Po = 0.081^2 x 2500 = 16.53
Iavg = 2 x 0.081 / 3.14 = 0.052
Pdc = 400 x 0.052 = 20.71
Pd = Pdc - Po = 20.71 - 16.53 = 4.18 (both tubes)

Class A Calculation
===
Ia = 400 / 5000 = 0.08
Ia' = 0.08 + 0.03 = 0.11
Vt = 260
Vrms = (400 - 260) / SQRT(2) = 99
Po = 2 x (99^2 / 5000) = 3.92
% into Class A = 3.92 / 16.53 = 23.71%

For Class A
Vrms = (400 - 240) / SQRT(2) = 113.14
Po = 2 x (113.14^2 / 5000) = 5.12

Last edited by jazbo8; 17th January 2013 at 12:31 AM.

 17th January 2013, 01:01 AM #19 diyAudio Member     Join Date: Dec 2008 Location: Dau Thanks for all your comment guys... @Jazbo...I can't see the picture you attached...i hope you drawn your loadlines for me to refer...I greatly appreacite it... kindly re attach the picture... Okay guys...how about reducing the OPt impedance to 5k by making the 16ohm secondary for 8 ohm speaker...does it make sense?...i just dont know if the opt can handle the primary current needed and how it will affect the bandwith?.
diyAudio Moderator

Join Date: Jan 2011
Location: In Transient
Quote:
 Originally Posted by Junm Thanks for all your comment guys... @Jazbo...I can't see the picture you attached...i hope you drawn your loadlines for me to refer...I greatly appreacite it... kindly re attach the picture... Okay guys...how about reducing the OPt impedance to 5k by making the 16ohm secondary for 8 ohm speaker...does it make sense?...i just dont know if the opt can handle the primary current needed and how it will affect the bandwith?.
Sorry, I thought I attached it... might be dropbox acting up. Yes, 5K would be a much better load, but may exceed your OPT's 20W rating.Try play with the curves a bit to make it work...

Last edited by jazbo8; 17th January 2013 at 01:12 AM.

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