DavidBohmfan,
The data sheet says 8 Ohms.
Were you hoping for:common, 4, 8, and 16 Ohms to be able to ground 4, and use Common and 16 Ohm for cathode feedback?
The transformer is built with very many layers of interleaving, and with a single 8 Ohm output, is probably the best it can be.
But to wind it with a common, 4, 8 (9), and 16 would lower the performance of that transformer.
Just my opinions
The data sheet says 8 Ohms.
Were you hoping for:common, 4, 8, and 16 Ohms to be able to ground 4, and use Common and 16 Ohm for cathode feedback?
The transformer is built with very many layers of interleaving, and with a single 8 Ohm output, is probably the best it can be.
But to wind it with a common, 4, 8 (9), and 16 would lower the performance of that transformer.
Just my opinions
Hello,
Maybe you can get some idea from my build:
https://www.diyaudio.com/community/threads/push-pull-807-amplifier-without-global-nfb.384100/
I think you need either high B+ voltage or lower OPT turns ratio for anything around 10 to 15 Watts. You can use e.g. 600V for the anode and 300V for g2 with your OPT. 300...350V simply not going to give enough voltage swing at the secondary.
Maybe you can get some idea from my build:
https://www.diyaudio.com/community/threads/push-pull-807-amplifier-without-global-nfb.384100/
I think you need either high B+ voltage or lower OPT turns ratio for anything around 10 to 15 Watts. You can use e.g. 600V for the anode and 300V for g2 with your OPT. 300...350V simply not going to give enough voltage swing at the secondary.
12.5W @ 8 ohms = 10V rms. That is 14.1V peak. Using the Sowter U082 it has turns ratio 31.6 : 1. The primary peak will be 14.1 x 31.6 = 445V. You would need some 500V B+ or more. The 807 can't be triode connected (or UL) in this case, because the g2 voltage is limited to 300V. (Although I am using it in UL with B+ 350V without any issue).
Oui avec un tel transfo il te faut plus de B+.
Jetez un œil à Vtadiy.com, cela vous sera utile.
le mien est en 4k.
Have a look to the STC 807 report.
regards
Jetez un œil à Vtadiy.com, cela vous sera utile.
le mien est en 4k.
Have a look to the STC 807 report.
regards
My amp allows me to adjust the b+ and bias per tube. It uses Monolithic Magnetics 8k transformers. Looking around for operating points for the 807 in triode PP I came to Duncan’s and saw that it recommends 320v 40ma into 8k for a whopping 6 watts of class A power. It is also claiming .6% of THD though without any details on how that measurement was made. I gotta say, the amp positively sings with these settings.
https://tdsl.duncanamps.com/show.php?des=807
Saw these numbers above from Morgan Jones and thought I’d give them a try. More power is better right? I don’t have any way of measuring my amp but it really didn’t sound as good at these settings as compared to the ones from Duncan’s. The bass is weaker and there seems to be a haze throughout the range. I wonder what is going on? I am running Cossor branded vt60a tubes which are supposed to be equivalent to the 807 but maybe there’s a difference at higher powers? They certainly work incredibly well at the figures for 807 on Duncan’s. Or maybe there’s something in the circuit or transformer or whatever. Point is that you might want to experiment at different operating points for best sound. I know people cringe on getting that few watts out of a pair of 807 but it works well with my speakers and listening habits.
807s will run in triode mode with up to 400Vp. Early American Williamson amplifiers used the 807 this way and they were found to hold up fine. You can get 12wpc from triode-wired 807s, depending on the load. The Stancor Williamson kit ran therm just this way and you can find examples of these amps with the original 807s still operating.
Sure. I guess my question is what operating point sounds/measures better? Given the same transformer, would we expect the same performance at 320v 80ma vs 400 116ma? Obviously there would be more power at the higher voltage but it measure as well? I assume Williamson was aiming for max power, did distortion or sound quality of sort suffer to get that power?
Williamson was aiming for bandwidth and very low distortion. For some rough distortion figures for an 807 Williamson, you can see the "Musician's Amplifier" article and the Stancor brochure. Sarser and Sprinkle acknowledge that the 807 cannot measure up power-wise to the KT66, but they were difficult to obtain in the US at theat time:
https://dalmura.com.au/static/Musicians Amp Audio 1949.pdf
http://www.technicalaudio.com/pdf/G...Linear_Williamson_Amplifier_w_A-8054_xfmr.pdf
https://dalmura.com.au/static/Musicians Amp Audio 1949.pdf
http://www.technicalaudio.com/pdf/G...Linear_Williamson_Amplifier_w_A-8054_xfmr.pdf
Why would you use the same transformer for push pull triode wired 807 tubes that have quiescent voltage and current of:
320v 80ma vs 400 116ma?
You might have a higher damping factor in the Class A region of one of those two setups.
You will have to look at the triode wired curves, check the slope of the plate impedance, rp, at those two different operating points.
320v 80ma vs 400 116ma?
You might have a higher damping factor in the Class A region of one of those two setups.
You will have to look at the triode wired curves, check the slope of the plate impedance, rp, at those two different operating points.
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Because that is what is in my amp and I can set those operating points. Like I said, the 320v sounds great but thought I would try the higher operating point because why not? The amp is designed to allow me to use different operating points, potentially with a few different types of output tubes. I’ll admit to not knowing why one operating point will work well and the other does not. This is the transformer in my amp:
http://monolithmagnetics.com/sites/default/files/B-8_8k_0.pdf
And this is the amp:
https://www.head-fi.org/threads/oblivion-ultrasonic-studios.902926/page-444#post-17216420
I don’t remember whIch circuit design was used but it was a pretty standard one, no gyrators or followers or anything. The B+ is regulated and can be run between 250v-400v. The regulator is rated at 20 watt dissipation. The upshot to that is that I am limited to 30ma per tube when I run it at 250v But can apply more as I go up in voltage.
Anyway, I don’t know enough to know why the different operating points sound different. Was hoping to hear some likely explanations, hope the info wasn’t too vague.
http://monolithmagnetics.com/sites/default/files/B-8_8k_0.pdf
And this is the amp:
https://www.head-fi.org/threads/oblivion-ultrasonic-studios.902926/page-444#post-17216420
I don’t remember whIch circuit design was used but it was a pretty standard one, no gyrators or followers or anything. The B+ is regulated and can be run between 250v-400v. The regulator is rated at 20 watt dissipation. The upshot to that is that I am limited to 30ma per tube when I run it at 250v But can apply more as I go up in voltage.
Anyway, I don’t know enough to know why the different operating points sound different. Was hoping to hear some likely explanations, hope the info wasn’t too vague.