Which speaker tap when going from UL to triode

scottw · 5th July 2008, 06:52 PM

I have an amp with the ubiquitous PP UL EL34 output with a 4300:4,8,16 OPT.

When you change the output to triode mode, as i understand it, the transformer load is less than ideal. Could you improve the load for triode mode by changing which secondary tap you use? In other words, if you have 8 ohm nominal speakers could you improve the load for the triode strapped EL34 by using the 4 or 16 ohm taps? What about 6 ohm nominal speakers?

Thanks,

Scott

kenpeter · 5th July 2008, 08:31 PM

A loudspeaker can easily vary from 2 to 90 ohms depending what
it is asked to do and wether or not it abuses Zobels to fake a more
stable impedance...

Use whichever tap sounds best, and stop worryin about it.

andyjevans · 5th July 2008, 11:01 PM

Use whichever tap sounds best, and stop worryin about it.>>

Exactly! Could not have put it better.

ray_moth · 6th July 2008, 12:03 AM

For EL34, the 'ideal' P-P load normally recommended in tube manufacturers' data sheets (e.g. Mullard) for push-pull operation is 6.6k for UL and 5k for triode.

Neither of these modes is all that critical (unlike pentode mode) and I doubt if it matters at all if you continue to use the same speaker tap when you change from one to the other. You might possibly notice a slight reduction in both maximum output power and distortion.

My OPT was designed for EL34 in pentode mode, giving a load of 3.5k P-P but I wanted to use triode mode. By using the 4 ohm tap for my 8 ohm speaker, I got 7k P-P, which was 50% higher than recommended for triode mode, but it sounds fine.

scottw · 6th July 2008, 02:20 AM

kenpeter & andyjevans,

Me no worry, just curious. Transformers are still kind of a mysterious "black box" to me.

ray_moth,

Thanks for the details. Looks like the 4.3k ohm OPT will be "close enough" to the spec'd 5k ohm. Guess that's why I've never read about anyone recommending using a different output tap when changing to triode mode.

Thanks,

Scott

5th July 2008, 06:52 PM	#1
scottw diyAudio Member Join Date: Feb 2004 Location: Kalifornia	Which speaker tap when going from UL to triode I have an amp with the ubiquitous PP UL EL34 output with a 4300:4,8,16 OPT. When you change the output to triode mode, as i understand it, the transformer load is less than ideal. Could you improve the load for triode mode by changing which secondary tap you use? In other words, if you have 8 ohm nominal speakers could you improve the load for the triode strapped EL34 by using the 4 or 16 ohm taps? What about 6 ohm nominal speakers? Thanks, Scott __________________ "The Adobe Updater must update itself before it can check for updates. Would you like to update the Adobe Updater now?" -Adobe Updater

6th July 2008, 02:20 AM	#5
scottw diyAudio Member Join Date: Feb 2004 Location: Kalifornia	kenpeter & andyjevans, Me no worry, just curious. Transformers are still kind of a mysterious "black box" to me. ray_moth, Thanks for the details. Looks like the 4.3k ohm OPT will be "close enough" to the spec'd 5k ohm. Guess that's why I've never read about anyone recommending using a different output tap when changing to triode mode. Thanks, Scott __________________ "The Adobe Updater must update itself before it can check for updates. Would you like to update the Adobe Updater now?" -Adobe Updater

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5th July 2008, 08:31 PM	#2
kenpeter diyAudio Member Join Date: Nov 2007 Location: Dallas	A loudspeaker can easily vary from 2 to 90 ohms depending what it is asked to do and wether or not it abuses Zobels to fake a more stable impedance... Use whichever tap sounds best, and stop worryin about it.

5th July 2008, 11:01 PM	#3
andyjevans diyAudio Member Join Date: Sep 2003 Location: London	Use whichever tap sounds best, and stop worryin about it.>> Exactly! Could not have put it better.

6th July 2008, 12:03 AM	#4
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	For EL34, the 'ideal' P-P load normally recommended in tube manufacturers' data sheets (e.g. Mullard) for push-pull operation is 6.6k for UL and 5k for triode. Neither of these modes is all that critical (unlike pentode mode) and I doubt if it matters at all if you continue to use the same speaker tap when you change from one to the other. You might possibly notice a slight reduction in both maximum output power and distortion. My OPT was designed for EL34 in pentode mode, giving a load of 3.5k P-P but I wanted to use triode mode. By using the 4 ohm tap for my 8 ohm speaker, I got 7k P-P, which was 50% higher than recommended for triode mode, but it sounds fine.

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