How would you drive an EL509 in enhanced triode mode.

[Sorento]

.... I have searched through the topic but did not find the schematics that you have used to build the amplifier ....
If I am right you could just remove the resistor ...

maybe not so in Danielak's as the 7.5k is part of the nfb loop ... ?
https://www.diyaudio.com/community/attachments/el509-6bm8-sweep-tube-amp-pdf.921208/

 

[Bas Horneman]

I have searched through the topic but did not find the schematics that you have used to build the amplifier.

Sorry only saw your question today.

 

[Francois G]

Hi Bas,
How do you like your Danielak EL509 “Enhanced Triode” amp? Is it worth building? I’m eagerly awaiting your assessment; you may recall I have a pair of the One Electron UBT-1s in storage.

 

[Bas Horneman]

Hi Francois,

First impression when first put in my main system was good. But I started hearing something strange....(Back in May of last year) and decided to investigate. But never did. This week it will go on the bench. I suspect the 6bm8 pulls.

 

[Bas Horneman]

Hi Francois, I like it! Lovely amp worth building . But... without the feedback. Unlistenable with the feedback. Perhaps I did something wrong. But when I cut it out the amp came alive. Before that it sounded as if it was governed. Enjoying it as 'we speak'.. Track after track. Because it's late at night. Just pop music.

 

[Bas Horneman]

 

[Francois G]

Thanks Bas. Looks great! Congratulations.

Could you please mark up the schematic (#142) with the changes you made, if any. Photo of the marked-up schematic would be fine.

Also, have you measured the power output (and perhaps done other measurements) performance?

 

[Bas Horneman]

Will do. No measurements possible. I have no equipment.

 

[Bas Horneman]

Sound was very soft because it was late at night and have to think about the neighbours. I could not drag myself away from listening. Kept playing song after song and not zapping to the next constantly. I am a very happy chappy!

 

[Bas Horneman]

This is what it became. Just global feedback removed. YMMV. And not potentiometer for volume control. Just a 100k resistor in lieu of the pot.

 

[Kay Pirinha]

I'd not remove global NFB, but modify the circuitry in order to remove the bias trimpot's impact on it.

Best regards!

 

[Chris Hornbeck]

What's the purpose of the positive feedback in the driver stage?

All good fortune,
Chris

 

[Bas Horneman]

 

[Bas Horneman]

 

[Bas Horneman]

Some shots of the inside.

 

[Kay Pirinha]

What's the purpose of the positive feedback in the driver stage?

Hi Chris,

Bob Danielak explains it in the bulletin that already was linked to some postings above. Anyway, I also don't think it is really necessary and omitted it in my rendition of this amp.

Best regards!

 

[Francois G]

Bas,
Excellent! Enjoy your listening and music.

Thanks for fessing up to all you secrets; finally! 😉 And thanks for taking the trouble to share your modifications to Mr. Danielak’s design.

Interesting to note that you are running B+ of 400 Vdc with the (relatively) low impedance UBT-1. It makes more intuitive sense to me than the original 5k output transformer in the EL509 circuit, but I have not checked the loadlines (I think I have seen a screen-drive graph somewhere). Glad to know it sounds good.

One final question - what is the cathode current of the EL509 (for future builders to check)?

 

[Bas Horneman]

One final question - what is the cathode current of the EL509 (for future builders to check)?

Will check..might take a week or so.....

 

[Bas Horneman]

Pin numbers are wrong for the EL509S by the way. Will update soon.

 

[Bas Horneman]

Oeps