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Old 16th December 2013, 07:42 AM   #1
6J7 is offline 6J7
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Default spudnik, spudMiG ?

Just finished these monoblocs, driven by an asus xonar D/A converter.

Input transformers are LL1681 (1:13)

It sounds pretty good

Unfortunately I don't see how to remove these coupling caps because of fixed bias and I don't like the idea of cathode bias with that kind of tube..
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Last edited by 6J7; 16th December 2013 at 07:57 AM.
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Old 16th December 2013, 07:55 AM   #2
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Another view with meters, they are directly in the path to measure anode current on each plate.
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Old 16th December 2013, 08:05 AM   #3
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If you can split the OT primary you can load each plate with a CCS followed by a capacitor before each half of the primary winding. I have used this successfully in one of my designs and it ensures perfect DC balance with grounded cathode and no coupling caps.

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Old 16th December 2013, 04:58 PM   #4
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Looks like some resistors are missing in the feedback arrangement.
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Old 16th December 2013, 08:31 PM   #5
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Quote:
Originally Posted by 6J7 View Post
Just finished these monoblocs, driven by an asus xonar D/A converter.

Input transformers are LL1681 (1:13)

It sounds pretty good

Unfortunately I don't see how to remove these coupling caps because of fixed bias and I don't like the idea of cathode bias with that kind of tube..
get the Feedback from the primary

M.
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Old 11th January 2014, 07:53 PM   #6
6J7 is offline 6J7
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Thank you for your input.

Quote:
Looks like some resistors are missing in the feedback arrangement.
No.

This amp sounds fine with Cornwall III's despite the DF a little bit on the low side.

Time to start another spud, this time with GU17 and CFB
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Old 11th January 2014, 10:11 PM   #7
seppoa is offline seppoa  Sweden
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One possibility to eliminate the coupling cap is to connect the input trafo directly to the grid, and attach the bias to the ground end of the trafo, parallel to a gridleak and a cap to ground. Not sure thou if it will improve the sound, as the signal current passes thru the cap?
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Old 12th January 2014, 12:23 AM   #8
Zekk is offline Zekk  Singapore
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Hi 6J7... That's gorgeous! A thing of beauty is a joy forever. Love those exotic tubes. Wish to built one but do not have a reliable schematic.

BTW, where did you buy those anode caps?

Thanks for sharing.
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Old 12th January 2014, 01:23 AM   #9
lhgin is offline lhgin  Malaysia
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1:13 input transformer?

did you manage to measure the frequency response? i'm just wondering if there would be setback with such a high step-up ratio on the input side.

thanks!
ken
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Old 12th January 2014, 03:03 AM   #10
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The input impedance looks like it is about .29 Ohm? (x4 for differential)
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Last edited by smoking-amp; 12th January 2014 at 03:10 AM.
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