Mikael Abdellah's kt88, (LOADLINES)

soundbadger · 2nd February 2008, 10:12 AM

can anyone help me,
i am trying to work out this scehmatic:
http://www.diyaudio.com/forums/attac...amp=1119993206

ive heard people in this forum saying that the kt88s are operating at 75mA but when i draw the load line for a HT voltage of 400v and a primary impedance of 5Kohms (like on the schematics) the anode voltage at 75mA would only be about 60v,
can anyone help me
cheers

Svein_B · 2nd February 2008, 10:45 AM

The DC conditions define your operating point.

The load impedance define your dynamic (AC) loadline, centered on the operating point.

SveinB.

soundbadger · 2nd February 2008, 11:01 AM

so should the operating point be in the middle of this ac loadline, because if 75mA is the operating current then it is not anywhere near the center of the line.

also could you explain what you mean by DC and AC conditions, how should i go about calculating my operating point and current when i know my opt primary impedance and my HT voltage.

i thought i understood this, but working through this amp i dont seem to get the same figures as everyone else

thanks

ed

soundbadger · 2nd February 2008, 11:41 AM

after a bit more reading of morgan jones book i think i have it.

if i do ht over rl 400/5000 i get 80mA

so if i wanted a cathode bias voltage of 37.5v i would do 37.5/0.080 and get about 470 ohm

or about 440ohm for a bias voltage of 35v

could anyone how has built this amp let me know if this sound right

cheers

ed

porkchop61 · 2nd February 2008, 01:11 PM

I have some voltage charts for this amp on my web page.
I have them for kt88's as well as el34's, running in all three modes (UL, Triode, Pentode). This might help you see where this amp operates.
Glenn

KT88 SE full schematic w/voltages

arold19 · 19th April 2011, 01:09 AM

It is better with 470 or 560 Ohm cathode resistor??? Maybe 500 Ohm is ¨perfect¨?

arold19 · 3rd January 2012, 02:30 AM

Why there a 100 Ohm resistor on the UL transformer tap on the (porkchop61) schematic and there no resistor on the Mikael schematic??
Also, can enyone answer me about the cathode risistor?

Thank.

2nd February 2008, 10:12 AM	#1
soundbadger diyAudio Member Join Date: Sep 2007	Mikael Abdellah's kt88, (LOADLINES) can anyone help me, i am trying to work out this scehmatic: http://www.diyaudio.com/forums/attac...amp=1119993206 ive heard people in this forum saying that the kt88s are operating at 75mA but when i draw the load line for a HT voltage of 400v and a primary impedance of 5Kohms (like on the schematics) the anode voltage at 75mA would only be about 60v, can anyone help me cheers

2nd February 2008, 01:11 PM	#5
porkchop61 diyAudio Member Join Date: Aug 2004 Location: Mansfield, Connecticut	I have some voltage charts for this amp on my web page. I have them for kt88's as well as el34's, running in all three modes (UL, Triode, Pentode). This might help you see where this amp operates. Glenn KT88 SE full schematic w/voltages __________________ "Imagination is more important than knowledge"

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2nd February 2008, 10:45 AM	#2
Svein_B diyAudio Member Join Date: Oct 2005	The DC conditions define your operating point. The load impedance define your dynamic (AC) loadline, centered on the operating point. SveinB.

2nd February 2008, 11:01 AM	#3
soundbadger diyAudio Member Join Date: Sep 2007	so should the operating point be in the middle of this ac loadline, because if 75mA is the operating current then it is not anywhere near the center of the line. also could you explain what you mean by DC and AC conditions, how should i go about calculating my operating point and current when i know my opt primary impedance and my HT voltage. i thought i understood this, but working through this amp i dont seem to get the same figures as everyone else thanks ed

2nd February 2008, 11:41 AM	#4
soundbadger diyAudio Member Join Date: Sep 2007	after a bit more reading of morgan jones book i think i have it. if i do ht over rl 400/5000 i get 80mA so if i wanted a cathode bias voltage of 37.5v i would do 37.5/0.080 and get about 470 ohm or about 440ohm for a bias voltage of 35v could anyone how has built this amp let me know if this sound right cheers ed

19th April 2011, 01:09 AM	#6
arold19 diyAudio Member Join Date: Nov 2002 Location: montreal	It is better with 470 or 560 Ohm cathode resistor??? Maybe 500 Ohm is ¨perfect¨?

3rd January 2012, 02:30 AM	#7
arold19 diyAudio Member Join Date: Nov 2002 Location: montreal	Why there a 100 Ohm resistor on the UL transformer tap on the (porkchop61) schematic and there no resistor on the Mikael schematic?? Also, can enyone answer me about the cathode risistor? Thank.

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