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desperateaudio 1st December 2008 10:58 AM

6as7/6080 Se Otl
2 Attachment(s)
Attached is a schematic posted here a few years back from I believe Joel on a single ended OTL using 6080/6AS7's driven by a single 6SN7. Has anyone built this? I am thinking about giving it a go. The only real change I would think to make right off the bat is to give each cathode a resistor as I am under the impression that the 6080/6AS7 should have each cathode held to current on its own. Does anyone else have any thoughts?


JBLoudg20 1st December 2008 12:06 PM

My only suggestion is to make sure you sink those cathode resistors well. They will get VERY hot.

I have built a very similar design, and it sounds great. I think you'll love it.

poynton 1st December 2008 12:24 PM

I have been thinking of building a variant of this.

How would you couple the output to seperate cathode resistors?

What about the grid bias?


desperateaudio 1st December 2008 05:20 PM

I would put a 250ohm resistor on each cathode and tie the base of each together. I parallel that gets me to 41.3 ohms and the original schematic shows 40ohms for the top resistor. then i would go and attach that to the final 40ohm resistor to ground and tie the grid resistor in between as originally designed. I will drawin it up and post it.


desperateaudio 1st December 2008 05:48 PM

Do either of you gents have the schematics for the OTL's you discuss in your responses to my post?

I will pot my marked up schematic in a few hours.


Klimon 1st December 2008 07:10 PM


Do either of you gents have the schematics for the OTL's you discuss in your responses to my post?
I'll second that interest. BTW the schematic desperateaudio posted emerged from this thread:


desperateaudio 1st December 2008 11:18 PM

Yes that is where I got it from. I have an email into Joel to see if he ever built it but no response as of yet. I will post the marked up schematic with the resistor change in the AM as I had an emergency at home.

poynton 2nd December 2008 03:57 AM

The circuit I was thinking about is the one with a cathode choke. I think it is in that thread although not a very clear picture. It dates from the '50s.


desperateaudio 2nd December 2008 11:10 AM

Yeah a few people had raised some problems with that design which i was unable to completely figure out so i decided on the one i attached. The minute i can get into work here today i will post the schematic revisions for comment.

JBLoudg20 do you have the schematic of your's?

Thx in advance.

poynton 2nd December 2008 11:52 AM

I have read several reports (where?) from people that this design does work. ( )

On your proposal, where is the output cap going to be fixed??


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