Hey All, thanks again for all the help! It's made the early planning stage much easier. The biggest change is a lateral shift in output tube. This morning I bought four Winged 'C' 6N13S tubes. They were also billed as 6AS7's but they aren't really the same. They seem to be an improvement. The grid voltage is only -30 volts so they should be easier to drive. And the cathode resistor is only listed as 250 ohms. I don't have an audio data sheet for this tube so if anyone has one it would be much appreciated.
I did find a schematic that listed a 2500 ohm output transformer primary with a rated power output of 10.5 watts. With four tubes I intend to run the outputs in push pull parallel. If I'm correct that would drop the plate to plate to 1250 or so and give a power output of around twenty watts.
The purpose of this amp is to build an all triode 20 watt amplifier with little or no feedback. Since triodes produce mostly even order distortion and push pull tends to cancel even order distortion that might work out well. Another target is to make the amplifier as simple as possible. Cathode bias and AC filaments, old school.
Power supply will be solid state. This puppy will have a B+ supply of almost an amp so there would need to be too many rectifiers to use tubes. And I don't want to complicate the power transformer with a five volt winding. Also, I'm going to need a big choke.
As for the front end? Basic layout will be a differential amp. I've used Edcor line matchers as input transformers with good effect, and they're cheap! With only a 60 or so volt swing needed to drive 6N13S a couple driver tubes come to mind, 12AU7, 6SN7/6CG7 or maybe 6N6P? Other suggestions are welcome.
With a B+ of 250 volts I won't have to isolate the drivers from the output tubes. So I'm inching out on a limb here and thinking of making the stages direct coupled?
And rather than handles I might put some wheels on it.
I did find a schematic that listed a 2500 ohm output transformer primary with a rated power output of 10.5 watts. With four tubes I intend to run the outputs in push pull parallel. If I'm correct that would drop the plate to plate to 1250 or so and give a power output of around twenty watts.
The purpose of this amp is to build an all triode 20 watt amplifier with little or no feedback. Since triodes produce mostly even order distortion and push pull tends to cancel even order distortion that might work out well. Another target is to make the amplifier as simple as possible. Cathode bias and AC filaments, old school.
Power supply will be solid state. This puppy will have a B+ supply of almost an amp so there would need to be too many rectifiers to use tubes. And I don't want to complicate the power transformer with a five volt winding. Also, I'm going to need a big choke.
As for the front end? Basic layout will be a differential amp. I've used Edcor line matchers as input transformers with good effect, and they're cheap! With only a 60 or so volt swing needed to drive 6N13S a couple driver tubes come to mind, 12AU7, 6SN7/6CG7 or maybe 6N6P? Other suggestions are welcome.
With a B+ of 250 volts I won't have to isolate the drivers from the output tubes. So I'm inching out on a limb here and thinking of making the stages direct coupled?
And rather than handles I might put some wheels on it.
6080 (6AS7, 6N13) is a really screwed choice if you are such a beginner, read again what Shoog commented on it.
Search for the topics on his and others' experiences with it. E.g.
Help designing a tube amp...
Ideas for a simple 6080/6AS7 Push-Pull amplifier
And, of course, this one:
Idea for a 2 tube 6080 PP amp.
Search for the topics on his and others' experiences with it. E.g.
Help designing a tube amp...
Ideas for a simple 6080/6AS7 Push-Pull amplifier
And, of course, this one:
Idea for a 2 tube 6080 PP amp.
6N13S is functionally identical to a 6080 apart from its dissipation.
I would go with something like a ECC99 as a driver. With the horribly low gain of a practical 6080 valve you can expect to need to go into positive grid territory to get your target 10Watts and that will need a strong driver with a reasonably high gain, not a combination easily found in triodes. Better yet a pentode driver would suit better. A more realistics expectation is 7watts from a pair.
I always found (and others agreed) that these valves sound best when driven hot at 100mA and just 100V of plate to cathode voltage.
Shoog
I would go with something like a ECC99 as a driver. With the horribly low gain of a practical 6080 valve you can expect to need to go into positive grid territory to get your target 10Watts and that will need a strong driver with a reasonably high gain, not a combination easily found in triodes. Better yet a pentode driver would suit better. A more realistics expectation is 7watts from a pair.
I always found (and others agreed) that these valves sound best when driven hot at 100mA and just 100V of plate to cathode voltage.
Shoog
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Joined 2009
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With these numbers you can get some 2 W (as PP) from one 6AS7G and then the output transformer should some 500 to 1k.
With planned 2.5 OPT hardly 1.5 W is possible.
So, to get the required 10 W, just 5 tubes should be put parallel
.I would like to know what is wrong with the well tested and fully functioning
construction with 12 W output power, 375 V supply voltage, 5k OPT and cathode bias, which I suggested??
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I want to build a simple all triode amplifier. Emphasis on simple. And I want enough power to drive 91db speakers. That means PPP with this tube to make it possible. I bought four Winged C 6N13S tubes and they cost all of $52.80. The seller claims they are all matched within 2%. Which may or may not be true. But to buy 8 JJ 300B's would be more than a grand!
Just need to find the transformers...
Just need to find the transformers...
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Chinese comrades even can get 35W from one driving it by a 6F1 tube. Cheap!
Finished 6N13P+6F1 Tube Amplifier Stereo Bluetooth Power Amp Lossless decoding | eBay
Finished 6N13P+6F1 Tube Amplifier Stereo Bluetooth Power Amp Lossless decoding | eBay
"All great discoveries happened because nobody explained that that was impossible!"
Good luck! ;-)
The seller would say anything to sell that soviet garbage.
You disagree to pay the full price for peach, so you buy a cheap potato and now wondering why it is not eatible? you gotta cook it. properly.
Why 8 pcs of 300 btw? 4 would be more than enough.
If you wanna save buy e.g. 6BX7GT. You can get a quad even for $20 and parallel them same way. With these you get better outcome, simple-&-common topology, and much less hustle of making it out.
Otherwise just copy-cat what others done with 6080, what you are dealing with is not that "simple".
Atma-sphere my orse?? No matter how much glorification the makers put in specs, I never yet heard an OTL that I liked. Neither any of my friends.
It just occurred to me that a bifilur primary and a dual parafeed arrangement for the output transformer might be the answer? That way the output transformer would only need to be capable of 20 watts and no DC current. I don't know much about transformers but it seems that any wire capable of 400ma of DC would not take kindly to only 15 or 20 watts of signal output? And they would be a lot cheaper.
And if I could find a simple 120 to 240 step up transformer the power transformer would be handled.
And if I could find a simple 120 to 240 step up transformer the power transformer would be handled.
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