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Old 2nd January 2013, 03:43 PM   #51
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The C1 Capacitor is under the E-Choke.

I have tried replacing the e-choke with a 5H choke I had from a other project, this changed B+ alot....

440V 100mVac

Output noise is reduced to 3,7mV still too much, but much better...

I don't think the E-choke is doing it's job
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Old 2nd January 2013, 08:51 PM   #52
euro21 is online now euro21  Hungary
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If your first cap less than 47uF, this type e-choke almost useless.
When C1 only 30uF, B2 hum about 7Vpp. At 47uF humming only 100mVpp.
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Old 2nd January 2013, 09:00 PM   #53
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Ok, I will try to change the first cap to 60uF, have read that others uset GZ37 with that big caps.
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Old 2nd January 2013, 11:23 PM   #54
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Found a bad mistake on the e-choke pcb, will try to fix it tomorrow...
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Old 3rd January 2013, 11:36 AM   #55
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Ok, good news.

The E-choke bug fixed a lot

B+ now has 10mV ac noise

And output noise is down to 2mV ac, hope I can improve this a little more when I get the layout cleaned up after all the trouble shooting.

But the MEC50 still isn't working as expected, will try to increase the current through it, to see if that changes things ?

Thanks for all the help

Suggestions for further improvements are welcome
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Old 3rd January 2013, 01:46 PM   #56
euro21 is online now euro21  Hungary
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I am glad that you found the problem.
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Old 4th January 2013, 04:45 AM   #57
dinoc is offline dinoc  United States
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How was the sounding?
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Old 5th January 2013, 02:11 PM   #58
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will report on the sound quality, when I finish both channels
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Old 8th January 2013, 02:56 PM   #59
Alexsk is offline Alexsk  Canada
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Default yamamoto A-09s design

Hi everyone,
I'd like to add a few comments. I am using C3M-300B topology for a few years now, I was experimenting with number of drivers for 300b, including number of C3M topologies.
From a number of available C3M-300B schematics, Yamamoto A-09S is probably the worst design. Yamamoto-sun basically copied Weco91 design, just replacing we810 driver with C3M and finding suitable G2 voltage ....well, Western Electric engineers use whatever tube was available that time. As a result driver runs with 91K anode resistor and rolling down at about 16 KHz due to Miller C of 300b. C3M is capable of running at 16ma anode I with 10K anode R, bringing bandwidth to 400kHz. That is Siemens recommended operation,,
150V G2, 10K anode R and 250 R cathode R. That i more or less the topology in Thorsten "Legacy" and Italian amp in Glass Audio. With some little tweaking, that is probably the best driver available.
Another note is regarding mentioned "electronic choke" . Please note that "real" choke is storing energy, where "electronic" is just a filter. It makes a huge deference in PS for power amplifier. Also, regulated DC heater supply for indirect heated C3M is waist of resources IMHO.
Someone may disagree with me, it is OK. Just built c3m/300b with really good output transformers , best c3m-300b coupling caps and (highly recommended) with non-electrolytic, oil caps in power supply. Then try both C3M topologies , measure amplitude/frequency and distortions and, most important, listen what sounds best to you.
BTW, what is IMHO is really great about A-09 is film caps in PS and 300B cathode. However 20uF for 300b cathode is a bit too low, bringing 20Hz to -2dB and, more important, changing LF phase. 33uF is a minimum, better 47. Oh, and speaking of a-09s PS. Yamamota-sun uses 400v film caps in the c3m B+ . It is OK when c#m is in-place. Without C3M 400v cap sees 435v across. Not exactly great engineering.
Thanks,
Alex
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Old 8th January 2013, 07:13 PM   #60
Alexsk is offline Alexsk  Canada
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Quote:
Originally Posted by fonnesbek View Post
Ok, good news.

The E-choke bug fixed a lot

B+ now has 10mV ac noise

And output noise is down to 2mV ac, hope I can improve this a little more when I get the layout cleaned up after all the trouble shooting.

But the MEC50 still isn't working as expected, will try to increase the current through it, to see if that changes things ?

Thanks for all the help

Suggestions for further improvements are welcome


Hi,
Your G2 chain is not working properly: you have 220k + 100k connecting B+ to G2/ Zeners. Current is 435-65 / 320 = 1.1 ma
C3M runs at 435-115/133=2.4 ma
G2 current is about 1/4 of Ia = 0.6 ma
That makes current flow through Zeners 1.1 - 0.6 = 0.5 ma Way not enough ! BTW in A-09s Zeners supplies via 50k+33k resistors.
Schematics of the Yamamoto A-09s is published somewhere in this thread, I strongly recommend you not to try make it better before you know exactly how it works,
just follow the design.
Good luck,
Alex
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