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Old 22nd February 2012, 02:10 AM   #101
scott17 is offline scott17  United States
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Originally Posted by debk View Post
One more LED bias question. I have done some reading on this circuit. Some are advocating biasing the 6N1P at around 3.2V or so (two 1.6V red LEDs) , instead of the 4V the specified resistor will give you. This bias point should run the tube at a slightly higher current. If you were to do this does the 47K plate load resistor need to be tweaked?

Also has anyone tried replacing the plate load resistor with a constant current source?

Debra
Biasing at 3.2V is about twice the current of the original circuit. To run this tube correctly, biased at 3.2V, you would be running at 8mA instead of 4mA. The plate resistor would be 22.2K. Conventional RC cathode resistor would be about 400R.

Have not used a CCS in this circuit. May be worth a try.

I would say try the circuit as designed first, 47K plate resistor, 1K cathode resistor, then proceed from there.

Scott

Last edited by scott17; 22nd February 2012 at 02:22 AM. Reason: cathode resistor correction
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Old 23rd February 2012, 06:56 PM   #102
scott17 is offline scott17  United States
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Originally Posted by scitizen17 View Post
Biasing at 3.2V is about twice the current of the original circuit. To run this tube correctly, biased at 3.2V, you would be running at 8mA instead of 4mA. The plate resistor would be 22.2K. Conventional RC cathode resistor would be about 400R.

Have not used a CCS in this circuit. May be worth a try.

I would say try the circuit as designed first, 47K plate resistor, 1K cathode resistor, then proceed from there.

Scott
You could also run at 3.2V bias with a 33K plate resistor at 6mA. It can be calculated several different ways. Just follow the load lines.
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Old 23rd February 2012, 08:06 PM   #103
debk is offline debk  United States
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I have been looking at the curves and will try a few operating points. I will of course build it stock and then experiment with it. Should be a lot of fun.

I want to try the led bias and maybe a ccs plate load.

looking forward to building the amp

Debra
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Old 24th February 2012, 10:16 AM   #104
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Originally Posted by scitizen17 View Post
The capacitors are Panasonic:
DS371506-CA
DS371306-CA
Thank you so much!
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Old 26th February 2012, 01:00 AM   #105
debk is offline debk  United States
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Finished building the amp. What a great sounding amp. Very warm and detailed.
It was a lot of fun to build.


Click the image to open in full size.


Debra
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Old 26th February 2012, 01:17 AM   #106
scott17 is offline scott17  United States
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Finished building the amp. What a great sounding amp. Very warm and detailed.
It was a lot of fun to build.


Click the image to open in full size.


Debra
Wow Debra! No time like the present so they say. That was very quick. What are you going to do tomorrow?

I'm very glad you like the amp. Looks great! What are those KT88s? EAT?

I suppose experimentation with the driver cathode bias is next?

Best regards,

Scott
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Old 26th February 2012, 02:41 AM   #107
debk is offline debk  United States
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The KT88s are Shuguang Treasures. I have been very impressed with the Treasures and Psvane line of tubes.

Next I want to play around with led cathode bias. I also want to experiment with a CCS, I have some DN2540 mosfets in my parts bin I can use.

The amp is great as it is, it is dead quiet, and there is something to be said about it having no sand. But I like to play around and tweak things.


Debra
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Old 26th February 2012, 12:21 PM   #108
debk is offline debk  United States
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Been putting the amp through it's paces. Just played the album I always play first with a new amp. UHQR vinyl release of Supertramp Crime of the Century.

Other components used are a Bottlehead extended foreplay preamp, Bottlehead Eros phono stage. Speakers are Madisound BK-20 backloaded horns,with Fostex FE206 drivers.
The amp is dead quiet, quieter than my DIY 300b amp

On rock music the amp sounds better than my 300b amp. The Bass is deeper, and the music has great presence. Very good sound stage. I can sit on my couch with my eyes closed and easily become immersed in the music.

On solo piano music that I like to listen to alot. It is close to my 300b amp. The 300b is slightly more liquid and more detailed.

In all fairness, I expect this amp to improve as it breaks in. I didn't take the time to preburn in the coupling capacitors. The Mundorfs silver/gold oil I used in the build take a little time to smooth out, and the tubes are new also.

After some burn in time I will play with LED bias on the 6N1P, and maybe a CCS plate load.

All in all this is a fantastic sounding amp! The circuit layout is very well thought out. The instructions are very well done and the amp is a lot of fun to build.

Debra
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Old 27th February 2012, 02:47 AM   #109
scott17 is offline scott17  United States
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Originally Posted by debk View Post
Been putting the amp through it's paces. Just played the album I always play first with a new amp. UHQR vinyl release of Supertramp Crime of the Century.

I don't have that release, just the CD. Had not heard it in a while, listened to it tonight. It is a great album.

After some burn in time I will play with LED bias on the 6N1P, and maybe a CCS plate load.

Please keep us posted on your experiments with the LED bias, and CCS. That's also on my list of things to do.

All in all this is a fantastic sounding amp! The circuit layout is very well thought out. The instructions are very well done and the amp is a lot of fun to build.

Debra
Thanks so much for your great comments. I appreciate it.

Scott
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Old 27th February 2012, 09:26 PM   #110
debk is offline debk  United States
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Been playing the amp a lot over the last two days. Have about 20hrs or so on it. It is noticeably smoother now.
I will let it break in for about 100 hours or so and then try the led bias.


Debra
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