Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid..... - Page 80 - diyAudio
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Old 22nd August 2012, 05:53 PM   #791
6L6 is offline 6L6  United States
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Bump.

I'm breadboarding a 12B4 preamp and want this thread towards the top where it can be found easily.
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Old 22nd August 2012, 08:43 PM   #792
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Default Some thoughts

One point to note on the 12B4 power. It really helps drive the baseline noise floor to zero if you use a separate power supply. DC heaters are also a good idie.
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Old 22nd August 2012, 10:52 PM   #793
6L6 is offline 6L6  United States
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The plan is CRCLC with a 20H choke and lots of capacitance.

I will try DC heaters as well. Thanks for the tip!
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Old 23rd August 2012, 12:16 AM   #794
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I have had a half-breadboarded, half-finished build of Eli Duttman's 12B4 amp in my system for the last few weeks. I built it on two chasses and converted to DC heaters. I am very pleased.
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Old 29th August 2015, 07:38 AM   #795
jcdrisc is offline jcdrisc  Australia
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Mark, here is my take on a 12B4 linestage.
Broskie's TUBECAD is well worth the money
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File Type: pdf 12B4linestage.pdf (440.7 KB, 127 views)
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Old 29th August 2015, 07:57 AM   #796
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I think there is an error in the Vmax out on your report, such large difference between the + and - swing suggests relatively high distortion.
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Old 29th August 2015, 10:31 AM   #797
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That scenario would require approx 25v input: not a very likely condition to be encountered in reality. At normal input levels around 2v the swing would be confined to an area of the plate curves where the +ve and -ve negative excursions would be far closer.
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Old 29th August 2015, 10:40 AM   #798
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We must have missed school that day, the whole thread is about using the 12B4 as a line amp...
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Old 1st September 2015, 03:10 AM   #799
jcdrisc is offline jcdrisc  Australia
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Default noisy gas tubes

I make again the firm assertion that ALL gas tube regulators are noisy, fdegrove.
Look at any Tek tube scope psu. Tek uses a 1M/100n filter before the grid of the error amp to get rid of all the hash. Why any amp designer uses them is beyond my comprehension. I enclose here a noise generator from Scroggie's book where an 85A1 is the noise source
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Old 1st September 2015, 04:05 AM   #800
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All of my 12B4 builds used stacked gas regulators and the noise floor was exceptionally low. Perhaps if this was a high gain circuit like a tape head or phono stage it would matter a lot. Not the case here. In fact my bench H-V supply is an old Eico tube supply and it is even exceptionally quiet, no,worse than a similar range H-V bench supply I have.

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