GU-50 PP + 10k:16-8-4 Ohm ,20w OPT..what is the best to do? - Page 2 - diyAudio
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Old 16th January 2013, 05:39 AM   #11
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On such low B+ you have to drive it in AB2, look at curves, otherwise output power is limited by saturation.

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Old 16th January 2013, 07:51 AM   #12
palmas is offline palmas  Portugal
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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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Old 16th January 2013, 08:37 AM   #13
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Quote:
Originally Posted by Wavebourn View Post
On such low B+ you have to drive it in AB2, look at curves, otherwise output power is limited by saturation.

Click the image to open in full size.
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...
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Old 16th January 2013, 08:50 AM   #14
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Originally Posted by Junm View Post
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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Old 16th January 2013, 08:53 AM   #15
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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
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Old 16th January 2013, 09:19 AM   #16
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Quote:
Originally Posted by Junm View Post
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....
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Old 16th January 2013, 03:26 PM   #17
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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.
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Old 16th January 2013, 11:13 PM   #18
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Quote:
Originally Posted by Junm View Post
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

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Last edited by jazbo8; 16th January 2013 at 11:31 PM.
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Old 17th January 2013, 12:01 AM   #19
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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?.
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Old 17th January 2013, 12:07 AM   #20
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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...

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