Another Power Supply Question

soundbadger · 9th October 2007, 10:27 AM

right so to deisgn a power supply i need to know the voltage desired and the current that will be drawn,

but from the curves for the kt88 (my output tube of choice for my amp) i have noticed that when in triode mode (as i want a switch to allow mode changing) the kt88 idles at 60mA as opsoed to ultralinear mode at 80mA.

Tweeker · 9th October 2007, 10:46 AM

Anode voltage will be somewhat higher in triode mode, depending on regulation.

If choke input you must size the inductance for triode mode. Triodes like a stiff psu.

Hotswitching modes may be problematic.

soundbadger · 9th October 2007, 10:58 AM

i did i simulation of an idea in duncun psu designer and when i go from 120ma draw (both tubes in triode mode) to 160ma draw (both tubes in UL) i get a voltage drop of about 15V,,,

is there anything i can do about this?

oh and i wouldn't ever hot switch anyway to many expensive components to potentialy damage..

soundbadger · 9th October 2007, 11:07 AM

just to let you know the amp is kt88 based single ended design with an HT / B+ voltage of 500v....

Tweeker · 9th October 2007, 11:43 AM

About the only thing you can do to reduce or eliminate it is build a beefier supply with less losses, or active regulation.

A somewhat higher anode voltage in triode mode isnt a disaster (assuming it doesnt take parts past ratings), check for the current it will draw at this different operating point.

Alternate bias for triode mode is another possibility.

soundbadger · 9th October 2007, 11:57 AM

i think ill just work out what voltage it will be getting in in triode mode, draw an appropriate load line and have a look. as like you say the 15v increase shouldnt affect its behavior too much.

soundbadger · 9th October 2007, 12:22 PM

heres the schematic

soundbadger · 9th October 2007, 12:25 PM

and heres a plot of the voltages over the 2 current dains (the 400v line is for the preamp) at 5 seconds the main drain switches from 120mA to 160mA.

zigzagflux · 9th October 2007, 02:13 PM

That 31 ohm resistance for the transformer seems a little low. That would be a fairly large transformer. You sure about that?

soundbadger · 9th October 2007, 03:31 PM

no not sure at all, neither am i sure of the cap's resistance ,,

they are just the figures that were on the parts in the psu designer,,, i should adjust them accordingly but i dont know what to ,,, a bit of reading might be order...

9th October 2007, 10:27 AM	#1
soundbadger diyAudio Member Join Date: Sep 2007	Another Power Supply Question right so to deisgn a power supply i need to know the voltage desired and the current that will be drawn, but from the curves for the kt88 (my output tube of choice for my amp) i have noticed that when in triode mode (as i want a switch to allow mode changing) the kt88 idles at 60mA as opsoed to ultralinear mode at 80mA.

9th October 2007, 10:46 AM	#2
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	Anode voltage will be somewhat higher in triode mode, depending on regulation. If choke input you must size the inductance for triode mode. Triodes like a stiff psu. Hotswitching modes may be problematic. __________________ Be sure your foil hat has a good low impedance ground.

9th October 2007, 11:43 AM	#5
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	About the only thing you can do to reduce or eliminate it is build a beefier supply with less losses, or active regulation. A somewhat higher anode voltage in triode mode isnt a disaster (assuming it doesnt take parts past ratings), check for the current it will draw at this different operating point. Alternate bias for triode mode is another possibility. __________________ Be sure your foil hat has a good low impedance ground.

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9th October 2007, 10:58 AM	#3
soundbadger diyAudio Member Join Date: Sep 2007	i did i simulation of an idea in duncun psu designer and when i go from 120ma draw (both tubes in triode mode) to 160ma draw (both tubes in UL) i get a voltage drop of about 15V,,, is there anything i can do about this? oh and i wouldn't ever hot switch anyway to many expensive components to potentialy damage..

9th October 2007, 11:07 AM	#4
soundbadger diyAudio Member Join Date: Sep 2007	just to let you know the amp is kt88 based single ended design with an HT / B+ voltage of 500v....

9th October 2007, 11:57 AM	#6
soundbadger diyAudio Member Join Date: Sep 2007	i think ill just work out what voltage it will be getting in in triode mode, draw an appropriate load line and have a look. as like you say the 15v increase shouldnt affect its behavior too much.

9th October 2007, 02:13 PM	#9
zigzagflux diyAudio Member Join Date: Oct 2006	That 31 ohm resistance for the transformer seems a little low. That would be a fairly large transformer. You sure about that?

9th October 2007, 03:31 PM	#10
soundbadger diyAudio Member Join Date: Sep 2007	no not sure at all, neither am i sure of the cap's resistance ,, they are just the figures that were on the parts in the psu designer,,, i should adjust them accordingly but i dont know what to ,,, a bit of reading might be order...

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