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Old 28th October 2012, 02:15 PM   #1161
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OK thanks.
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Old 28th October 2012, 04:15 PM   #1162
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Quote:
Originally Posted by SGregory View Post
AC voltage on the heaters for the 6v6 was inho the way to go. I tried various DC set-ups including a SSLVR and all of them sounded dead to me. So I am back to a simple tranny and a resistor to keep the voltage down to 6.1V. It is a matter of opinion though.
No Hum.
Did you also try the 317 chip current source heater like in the original schematic by the way?
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Old 28th October 2012, 04:58 PM   #1163
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Yes, I did try it. If I recall correctly, it was a similar perception. Kind of dull, or missing the life. Hard to describe exactly. In truth none sounded really bad, just prefered the AC set-up better.
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Old 28th October 2012, 05:07 PM   #1164
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Is there there a bit different harmonic content in THD measurement when with AC heating?
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Old 28th October 2012, 05:48 PM   #1165
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This is what I have. I don't recall why I stopped testing it as I don't really like the trash that I see with the 60Hz harmonics. I know I had a significant reduction in 60,120,and 180Hz with DC.

Regarding the 1kHz signal and harmonics, virtually identical or at least no difference I could see. +/- 1 or 2dB

I recorded this almost a year ago, 30Dec11, so I am a little sketchy on all the details, but I know I had better traces for the AC filament
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Old 28th October 2012, 10:30 PM   #1166
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So red is some time not your best AC heating, blue is DC heating. 1kHz harmonics have a nice fall scale.
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Old 28th October 2012, 10:32 PM   #1167
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Salas. Did you try lifted AC heater.
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Old 28th October 2012, 11:22 PM   #1168
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Yes red is a not so good AC spectrum. If you recall I was having a bit of an issue back then with ground loops on my test bench. I know I have a clean one somewhere in my files, but that was a computer ago. The 60,120, and 180 Hz peaks were about the same magnitude however.
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Old 28th October 2012, 11:28 PM   #1169
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i heard reports by some local diy'ers that using a CMC on the ac filament yielded improvement, the choke is a ferite type sized to handle the current required...
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Old 28th October 2012, 11:38 PM   #1170
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Salas. Did you try lifted AC heater.
Not in this one. DC voltage source and DC current source. I preferred the later.
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