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Old 25th January 2010, 12:50 AM   #121
Zen Mod is offline Zen Mod  Serbia
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sorry , Ray - I didn't realize that is you asking , even if I salute your efforts and enthusiasm previously ;

unfortunately , I'm not so familiar with many of 12B4 premp variants , even if I participate earlier in thread , drawing one of first tube shunt regs ( pretty crude and simple , by demand) .
that thread - linked to our Serbian forum , is with CCS load for 12B4 ; I resume origin is from here , big DiyA , and variety of various CCS-es is pretty well xplained in article made by local (P10 and gang) , and you can find it here : http://choky.diyaudio.rs/downloads/d...-CCS-beta3.pdf .
unfortunately , schematics are crucial , so I can't even imagine ways how you are ( already been ) doing things like these .
if you are in mood for that - write specifically how we can help you , and I'll try ..... even if I'm pretty ignorant in many bits 'n' pieces locally available to you , just because I'm living on other side of big splash .
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Old 11th April 2011, 08:07 PM   #122
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Default IRFP9240 upgrade?

I checked this thread recently looking for an improvement of my 12B4 preamp. Will probably try that CCs cascode but would like to know if someone put another transistor than IRFP9240? Or any suggestions? Thanks.
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Old 12th April 2011, 03:27 AM   #123
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That's a good looking circuit, Eli. Have you tried it without the gridstoppers? If the circuit is naturally stable, the sound will be substantially improved without them.


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Old 12th April 2011, 06:00 AM   #124
Salas is offline Salas  Greece
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Originally Posted by crazyfrog View Post
Or any suggestions? Thanks.
IRF9610 is faster, same Vmax.
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Old 12th April 2011, 07:06 AM   #125
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Originally Posted by Zen Mod View Post
maybe this will help you :

12B4A preamp - DIYAudio.rs

pics and schematics aren't in Serbian , and you don't need to register to see graphics

edit: shunt reg is further down the thread , one per channel
Click the image to open in full size.

This is one of the best DIY executions I have ever seen!!
Have a look at the last page of the thread Zen Mod links to, guys!
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Old 14th November 2012, 01:36 PM   #126
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Default upgrade cap on cathode?

I have on hand two Blackgate caps NX 1000 F 25V. Would it be too much capacitance putting those on 12B4 cathodes?
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Old 16th November 2012, 09:17 AM   #127
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Seems 1000 F is not too much for bypassing but not necessary.
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Old 4th December 2016, 01:52 AM   #128
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I aways wondered, why not just cut off the #7 pin instead of putting a gridstopper on it?

Last edited by lt_texan; 4th December 2016 at 02:14 AM.
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Old 4th December 2016, 02:13 PM   #129
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Originally Posted by lt_texan View Post
I aways wondered, why not just cut off the #7 pin instead of putting a gridstopper on it?
That question calls for another: why two grid pins on 12B4?
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Old 4th December 2016, 03:15 PM   #130
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The two grid pins are probably for cooling. Typical television use may push the control grid slightly positive. The spec sheet shows grid current for +5 and +10 vollts.
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