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SE 811 amp schematic...
SE 811 amp schematic...
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Old 3rd October 2014, 12:06 PM   #21
knockbill is offline knockbill  United States
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Quote:
Originally Posted by artosalo View Post
This is the 811A SE amplifier I built some 4 years ago. Max. power output is some 15 W and the linearity is quite good even without any GNFB.
This looks simpler then other schematics I've looked at,,, The 680K pot is the volume control, correct? Any suggested substitutions for 6N1P, I like to use what I have, if possible...
I'm pretty new at this, and appreciate teh input and schematics...

Regards,
John
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Old 3rd October 2014, 02:40 PM   #22
artosalo is offline artosalo  Finland
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Quote:
Originally Posted by knockbill View Post
...The 680K pot is the volume control, correct? Any suggested substitutions for 6N1P...
680k pot is for adjusting the pentode stage to optimum distortion.
It is not very critical at all, but the schematic is from my prototype and I usually have some adjustments that are not actually needed, but usefull when prototyping.

I also used one half of 6N6P as a driver.
I assume 6DJ8 could be one that works, 6BL7 for sure...
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Old 3rd October 2014, 02:44 PM   #23
artosalo is offline artosalo  Finland
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Quote:
Originally Posted by multi View Post
Very few manufacturers, DIYer's ever give the out put impedance.
Phil
I usually do such measuremets to my prototypes and not that much listening tests. I never built this amplifier as a complete stereo version, only one channel prototype.
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Old 3rd October 2014, 02:47 PM   #24
knockbill is offline knockbill  United States
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Thanks again for teh info,,, I use pots in mock ups also, usually for dialing in FB...
Not sure I have teh tubes on hand to try your design, but I printed it and will keep it for reference,,,

Regards,
John
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Old 3rd October 2014, 02:48 PM   #25
artosalo is offline artosalo  Finland
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Quote:
Originally Posted by kmaier View Post
Would like to see a few pics of your amp if they are easily linked

Regards, KM
I found one:

Edit: A couple more with better resolution:

My output tube was soviet G811.
Attached Images
File Type: jpg 811A proto.jpg (36.9 KB, 677 views)
File Type: jpg L1000081.JPG (363.8 KB, 660 views)
File Type: jpg L1000085.JPG (359.9 KB, 649 views)

Last edited by artosalo; 3rd October 2014 at 02:51 PM.
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Old 7th October 2014, 01:04 AM   #26
knockbill is offline knockbill  United States
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I built one channel of the amp in post 12,,, Its rough, but works pretty well... Voltages are close to specs, and its running on 2 different FTs (AC, for now) so the B+ can be adjusted with a variac, without affecting teh heater V...
Looks promising, so far... DC heater supply is the way to go, tho...
Still trying to learn!!!

Regards,
John
Attached Images
File Type: jpg P7170007.jpg (601.1 KB, 594 views)
File Type: jpg P7170004.jpg (366.1 KB, 561 views)
File Type: jpg P7170002.jpg (522.5 KB, 186 views)
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Old 7th October 2014, 06:44 AM   #27
artosalo is offline artosalo  Finland
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My experience is that 811 works with better linearity at essentially higher supply voltage and load impedance.
What is the present operating point ?
And especially the grid current (without signal) ?
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Old 7th October 2014, 12:05 PM   #28
kmaier is offline kmaier  United States
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I always prefer a classic breadboard approach for new designs. It's much easier to make changes, much safer from inadvertent shorts with probes and loose components and you can easily move it around. Attached is a pic of the initial 3C24 SE amp. Granted, it takes a bit of extra time to do the initial breadboard, but you reuse much of it for later designs, as the BB was initially done for a SE with single-plate 2A3s.

Regards, KM
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File Type: jpg 3C24-BB.jpg (898.9 KB, 307 views)
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Old 7th October 2014, 12:17 PM   #29
knockbill is offline knockbill  United States
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Nice layout,,, I've used these "test mules" for 4-5 amp builds so far...I find it easier to be able to flip teh chassis over for access to the tube pins, and use a color code to follow wires...
If I am sure of teh circuit, I make a masonite "chassis" the same size as teh final chassis and try everything in its ultimate position, to make sure there's no hum before final assembly...
Whatever works, have fun...

Regards,
John

Last edited by knockbill; 7th October 2014 at 12:19 PM.
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Old 7th October 2014, 03:10 PM   #30
knockbill is offline knockbill  United States
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Here's some voltage readings I got, with the amp warmed up no signal, at 254VDC B+,,,, I added a 1.0/200V input cap, to protect CDP...
Other then the hum, it sounds pretty good...

811,,,340V Plate, 22V Grid
6V6,,, 268V Plate
6SN7,,, 69V Plate

Regards,
John
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