Straange triodes
- Thread starter Ned Sheats
- Start date
It is customary that related to a tube's ratings, the voltage potentials always reference the cathode. However, under typical operating conditions, the voltages reference ground.
Dave
Dave
Ned Sheats
New Member
Back on it again. I finally got the 22 watts I think I should have. The distortion was comong from the PI and I missed it somehow. It doesnt show any signs of pink plates even though the indicated current per plate in 85 Ma per tube at idle. Jumps up to 120Ma prior to clipping and settles right back down with signal removed. Measurements are with the conventional 1KHz sine.
I included a small amount of negative feedback to eliminate the wave form distortion. I dont want to push it any farther. Still would like to know why I am getting more output on the 16 ohm tap with an 8 ohm load than I am on the 8. I would like to thank everyone for all the suggestions and explanations. The prototype is done .. on to the Stereo version. BTW I am using a set of military 6080s for the prototype I have a quad of new Svetlana 6AS7s for the finished product. Hope they will handle the current.
I'll work on some pictures as soon as I can figure out how to upload them.
I included a small amount of negative feedback to eliminate the wave form distortion. I dont want to push it any farther. Still would like to know why I am getting more output on the 16 ohm tap with an 8 ohm load than I am on the 8. I would like to thank everyone for all the suggestions and explanations. The prototype is done .. on to the Stereo version. BTW I am using a set of military 6080s for the prototype I have a quad of new Svetlana 6AS7s for the finished product. Hope they will handle the current.
I'll work on some pictures as soon as I can figure out how to upload them.
Ned Sheats
New Member
Not a problem. I am using 2 6CG7s with a plate supply of 365. Gives me around180V PP drive. THose are driven by a 12DW7 amp and PI.
Ned Sheats
New Member
Yes I am going for push pull parallel so th OT primary is center tapped and the secondary at 4, 8, 16. What is puzzling me is that using an 8 ohm load on the 16 tap I get more (about 4) watts than I do if I properly connect the 8 ohm load to the 8 ohm tap. I have never seen this happen before.
knockbill
Lunatic Member
[QUOTE="Ned Sheats, post: 9192180included a small amount of negative feedback to eliminate the wave form distortion. I dont want to push it any farther. Still would like to know why I am getting more output on the 16 ohm tap with an 8 ohm load than I am on the 8. [/QUOTE]
It may be because the OPT you are using matches up better with output tube at that ratio,,,, I was just checking turns ratios today for the amp I'm working on, and 16 ohm tap came out closer than the 8 ohm tap to get the 5K spec the schematic called for...
Haven't tried it yet, with this tx, but it makes sense...
It may be because the OPT you are using matches up better with output tube at that ratio,,,, I was just checking turns ratios today for the amp I'm working on, and 16 ohm tap came out closer than the 8 ohm tap to get the 5K spec the schematic called for...
Haven't tried it yet, with this tx, but it makes sense...
Ned Sheats
New Member
This has been an education. I am finding with triodes its all about getting enough drive to these power hungry tubes.
My operating specs now ar 225 P, -105 bias, 9 V cathode, 55 Ma "0" signal, and wonders of wonders 25 watts prior to clipping which is now perfectly symmetrical. The main difference is the supply for the drivers is now 420V rather than 365.
I am again going to try to attach pictures but dont know if I should use "upload a file" or the camera icon. Well that didnt work... At least the site saved my info so now Ill try "upload a file".
My operating specs now ar 225 P, -105 bias, 9 V cathode, 55 Ma "0" signal, and wonders of wonders 25 watts prior to clipping which is now perfectly symmetrical. The main difference is the supply for the drivers is now 420V rather than 365.
I am again going to try to attach pictures but dont know if I should use "upload a file" or the camera icon. Well that didnt work... At least the site saved my info so now Ill try "upload a file".
Attachments
Ned Sheats
New Member
While I'm waiting for the second output transformer I need to clean up some loose ends. This puppy will have to be set up accurately because I have found there is no such thing as "matched pairs" or matched singles. In fact the 6080s take about 15 minutes to stop drifting around I have bought "matched sets" with 15% difference within the same tube. I has one "NOS (yeh right) that never did stop drifting. Thats what the stack of Ma meters in the picture is for. I will need to adjust bias on 8 triodes. My thoughts are running to 8 window op amp conparator circuits and a single LED per triode to indicate when the current is the same and at spec on each triode. Hopefully I can get a narrow enough window by using some precision resistors.
Now All I need to do is find the power for this circuit. It will be interesting, when I publish a print for this, to listen to all the "you could have just". LOL. Remember, with the exception of the output transformers and 6080s, most of this was stuff I had in the shop for working on SW receivers and other audio projects. I still have to much modify a PAS2 to get rid of hum and make the equalization somewhere near RIAA . The FM3 after a couple of tubes and a by the book alignment turned out better than I had ever expected.
Again thanks for all the hints, quips and quotes.
The Tri-odd kid.
Now All I need to do is find the power for this circuit. It will be interesting, when I publish a print for this, to listen to all the "you could have just". LOL. Remember, with the exception of the output transformers and 6080s, most of this was stuff I had in the shop for working on SW receivers and other audio projects. I still have to much modify a PAS2 to get rid of hum and make the equalization somewhere near RIAA . The FM3 after a couple of tubes and a by the book alignment turned out better than I had ever expected.
Again thanks for all the hints, quips and quotes.
The Tri-odd kid.
Hi Ned,
Have you seen this article. It might have some ideas for you about keeping the bias currents set. I haven't used the 6080/6AS7 family of tubes, but I've built this sort of differential amp and it really sounds good to me.
http://www.triodeguy.com/Triodeguy PDF files/6AS7 Current Balanced PP Amp.pdf
Best of luck,
John
Have you seen this article. It might have some ideas for you about keeping the bias currents set. I haven't used the 6080/6AS7 family of tubes, but I've built this sort of differential amp and it really sounds good to me.
http://www.triodeguy.com/Triodeguy PDF files/6AS7 Current Balanced PP Amp.pdf
Best of luck,
John
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jazbo8
Well-Known Member
It's a good design, however the output power is much reduced, not sure if it will meet Ned's needs.
tri-comp
Well-Known Member
Hi jazbo8,
Sorry, I got into reading this thread rather late and have first noticed your request today.
Here's the article you asked for.
About doing an 6AS7-PP amp., that's been on my to-do list for some time.
I actually don't have 6AS7's but I do own some NOS Svetlana 6H13C's that should perform just the same (Latin: 6N13S).
I am definately going to set them up with fixed bias and use a cathode-follower-drive to get into Grid-current territory.
Expecting something like 1-2KOhm P-to-P imp. of OPT should produce satisfactory results running class AB2.
DRIVING these beasts are NOT going to be easy and will absolutely require an amplifying stage between the P/I and the cathode-follower driver.
Sorry, I got into reading this thread rather late and have first noticed your request today.
Here's the article you asked for.
About doing an 6AS7-PP amp., that's been on my to-do list for some time.
I actually don't have 6AS7's but I do own some NOS Svetlana 6H13C's that should perform just the same (Latin: 6N13S).
I am definately going to set them up with fixed bias and use a cathode-follower-drive to get into Grid-current territory.
Expecting something like 1-2KOhm P-to-P imp. of OPT should produce satisfactory results running class AB2.
DRIVING these beasts are NOT going to be easy and will absolutely require an amplifying stage between the P/I and the cathode-follower driver.
I wouldn't count on the Svetlanas to handle those operating parameters. 1960's era JAN-6080WB's by Sylvania or RCA are the way to go IMO.
Good luck...looks like a neat project!
jazbo8
Well-Known Member
Yes, the 6080's appear to be more robust than the run-of-the-mill 6AS7's.
Thanks!