Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid..... - Page 61 - diyAudio
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Old 30th November 2006, 08:11 AM   #601
arnoldc is offline arnoldc  Philippines
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hi pengboon, around 80 something volts... IIRC
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Old 30th November 2006, 12:01 PM   #602
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Thanks, Arnold. So you have only a single 100uF BG (35V, I presume) in the CCS? I only ask because the original states 445uF + bypass, which is quite a bit more capacitance.

Quote:
adam, I'm sorry for the crappy schematic... the left side is the input from the bridge rectifier. The right side is the output to serve 2 channels.
I thank you for the schematic, whether you call it crappy or not.
So, the - point on the left comes from the bridge and the one on the right connects to ground, n'est-ce pas?
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Old 1st December 2006, 02:53 AM   #603
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HI
I would like to ask for some help please .
I'm planing to build these 12B4 preamp after the ArnoldC schematic . Unfortunately I don't find ZTX758 & LM317 CCS parts for the power supply .
Please if someone know from were I can order these parts let me know , or if you have at home I will gladly buy them .
Thanks ArnoldC for the schematic !!

Regards
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Old 1st December 2006, 05:31 AM   #604
arnoldc is offline arnoldc  Philippines
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Hi Adam, Brian Beck mentioned in a previous post that 100uF, 200uF or 220uF x 2 paralleled with quality film will do. So you can use whatever your fancy.

Yes the output from the bridge goes to the left side (+) (-) and the right side (+) (-) goes to the circuit. Make sure you have a heatsink on the MOSFET.

gaborbela, the ZTX and LM317 can be ordered from Farnell. Our local RS Components does not have the ZTX...
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Old 1st December 2006, 01:21 PM   #605
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FWIW I run my 12B4 linestage at a wimpy 21mA - it displays much more speed and articulation than at 30mA, which sounds thick and congested by comparison.
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And I also noticed the smoothness on the top end, with nice touch of decay compared to a really sparkling, sometimes strident character of the 30mA operating point.
Just thought I'd mention that you people would have an impossible time convincing anyone that attends the Amp Shootouts that I have ay my house from time to time that the 12B4 line stage sounds thick or congested when run at 30 ma. In fact just the opposite... it sounds better. I have been through all the avenues you guys are now exploring! Its pretty clear that you are adjusting the coloration of the 12B4 to compensate for defficiencies elsewhere......

Mark
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Old 1st December 2006, 01:54 PM   #606
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Mark A. Gulbrandsen




Just thought I'd mention that you people would have an impossible time convincing anyone that attends the Amp Shootouts that I have ay my house from time to time that the 12B4 line stage sounds thick or congested when run at 30 ma. In fact just the opposite... it sounds better. I have been through all the avenues you guys are now exploring! Its pretty clear that you are adjusting the coloration of the 12B4 to compensate for defficiencies elsewhere......

Mark

at least you can try various plate loads,including smaller ones
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Old 2nd December 2006, 05:35 AM   #607
mach1 is offline mach1  Australia
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Quote:
Just thought I'd mention that you people would have an impossible time convincing anyone that attends the Amp Shootouts that I have ay my house from time to time that the 12B4 line stage sounds thick or congested when run at 30 ma. In fact just the opposite... it sounds better. I have been through all the avenues you guys are now exploring! Its pretty clear that you are adjusting the coloration of the 12B4 to compensate for defficiencies elsewhere......
Nice one Mark. A while back I remember trying to convince you that a simple 12B4 with ccs would outclass your grounded grid linestage. After protestations to the contrary you actually built one - and now you are apparently the self appointed Grand Wazoo of twelvebeeforedom who has been down all the avenues others are now exploring.

Sorry mate, but coming from a guy who provides 'advice' stating that the 12B4 is not linear at 15ma (if you can read plate curves, just draw a horizontal line at 15mA to represent a ccs load and have a look at an operating point around 160 - 180V . If you can find a more linear transfer characteristic over a plus or minus 40-50V swing anywhere in tubedom please let me know) and that late manufacture JAN GE12B4 is the pinnacle of the species I might just pass on your latest gem.

FWIW I have collected and tried various vintage 12B4 tubes by RCA, GE, Mullard and Sylvania over a wide range of voltages and currents and therefore feel reasonably comfortable with my personal choice of tubes and operating point. I have also tried a variety of circuit / psu configurations and personally prefer a cascoded 10M45s or Gary Pimm plate CCS to the bypassed LM317 in the cathode arrangement you run.

You will recollect my reply to Arnold stated:

Quote:
FWIW I run my 12B4 linestage at a wimpy 21mA - it displays much more speed and articulation than at 30mA, which sounds thick and congested by comparison.
This comment was related to the tubes I run in MY linestage, and was intended to indicate to Arnold that (i) he wasn't the only one who had consciously made a decision to run his/her tubes at a fairly low current, and (ii) that perhaps we had similar sonic preferences. It was not intended to indicate that anyone who thought otherwise was a cloth eared miscreant.

Well, I hope your high testosterone, high current LM317 based linestage with the JAN tubes and depth charge output capacitors continues to provide state of the art performance for you and your shootout buddies. Meanwhile, I guess Arnold and I will have to adjust the coloration of our 12B4s to compensate for defficiencies (sic) elsewhere in our systems.

I genuinely hope you get round to trying a DHT linestage one day. Perhaps we might get a new thread - 'Yet another DHT line stage, or is the DHT better than the 12B4' ?

regards

pm
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Old 2nd December 2006, 07:16 AM   #608
Nordic is offline Nordic  South Africa
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LM317 is common as chips, you can't be looking hard enough
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Old 2nd December 2006, 07:23 AM   #609
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HI
Yes LM317 is common but what is the CCS letters there .
Another think I never used them so I tough better to ask than be sorry ...
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Old 2nd December 2006, 07:33 AM   #610
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Mach1, can you share your experience on the various types/brands of 12B4?

cheers!
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