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Old 24th March 2012, 06:15 PM   #101
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Quote:
Originally Posted by avp1 View Post
According to this Barefoot Sound | Vintageking.com you can get a nice 5.1 setup for around $20K. This not out of reach for many people - compare it with price of Honda Accord or other "affordable" car.
As I said, even with such nice monitors I still hear sound of monitors amplified by amps. I don't hear sounds as if they are alive. That's the problem between your theoretical conclusions and my practical experience.
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Old 24th March 2012, 06:15 PM   #102
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Hello Sy,
I just reread Jones 3rd Edition section on test method and results for medium mu tubes. Perhaps we see your inspiration to use D3A tubes. All the tubes were tested at 8ma and 19.5V RMS output. The results show an order to things at the test conditions. I think that there is still room for us DIYers to play with the “lesser” tubes.
I bought a box of 9AU7’s for a dollar each. I also bought a box of 6BK7’s that I have used for line output buffers. Also in the stash is a box of 12SN7’s mostly WWII vintage JAN RCA in the plain cardboard packaging of the time. They are all fun to play with. I have been playing with 5763 transmitter tubes as power output tubes, could be junk.
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Old 24th March 2012, 06:36 PM   #103
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Quote:
Originally Posted by DualTriode View Post
Hello Sy,
I just reread Jones 3rd Edition section on test method and results for medium mu tubes. Perhaps we see your inspiration to use D3A tubes.
You see correctly. Morgan gave me two of them to duplicate his test setup. Before I wired things up, I stuck a D3a into mine (CCS plate load, LED bias) to check its distortion spectrum, just for fun. I thought my test equipment was broken! I asked him if he had measured them before doing his 6SN7 work. He responded, no. I suggested that he had put the wrong tube on the bottom of his mu follower.
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Old 24th March 2012, 06:36 PM   #104
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If you want something more extreme, Vkf=200V for ECC99 let us work up to 800V
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Old 24th March 2012, 07:09 PM   #105
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I dont know about mathematical models, but in real life higher plate voltages require lower currents and higher negative bias voltages that lead to island-effect, when each gap between grid wires act as a separate deevice in ray deflecting mode, lots of them in parallel. I don't think how it can be more linear than in case of traditional usage.
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Old 24th March 2012, 10:15 PM   #106
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I know nothing of mathematical models of valves, I can barely handle LTSpice, but the sims are consistent with what you say

+B=650V i=6mA Vgk=-13V THD=0.074%
+B=800V i=4.5mA Vgk=-17V THD=0.058%

I will try to explain following the approach suggested by SY in post # 6, by using curves of post#49
Sorry, but are the only ones I have on hand.

On curves mu vs. I, at low Vak, clearly sees that as decreases the electron cloud, mu increases, reaching a maximum, and from there begins to weigh secondary emission, then mu decreases.
When Vak increases, the electron cloud is increasingly weak, whereas secondary emission is increasing, and mu decreases.
At high levels of Vak, mu tends to be linear, and its slope tends to decrease, then distortion decreases.

You may not like my physical interpretations, but I'm just a TV repairman.

Last edited by popilin; 24th March 2012 at 10:22 PM.
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Old 24th March 2012, 10:33 PM   #107
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You've basically got half the B+ across each tube (equal cathode resistors), so you can easily pick off the operating point on the characteristic curves (325V Vak). It's safely in the conventional space-charge region, no need for fanciful explanations.
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Old 24th March 2012, 10:54 PM   #108
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OK, I know how to do some calculations, but I did not say otherwise.
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Old 25th March 2012, 01:26 AM   #109
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In my childhood I read how to increase the gain of a small signal triode reducing the filament voltage.
How to explain this in a not fanciful way?
Or will that in this hemisphere the laws of physics are reversed, or the books are written the other way around? Or am I reading the wrong books?

Last edited by popilin; 25th March 2012 at 01:39 AM.
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Old 25th March 2012, 01:58 AM   #110
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Quote:
Originally Posted by Wavebourn View Post
As I said, even with such nice monitors I still hear sound of monitors amplified by amps. I don't hear sounds as if they are alive. That's the problem between your theoretical conclusions and my practical experience.
Actually for natural sound like frogs, surround is much better. It also has an advantage in reducing influence of room acoustic on resulting sound.
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