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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid.....

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#768
coffeedj said:
You can see that I've finished the first rev in the new post.

I'm really impressed with the bench performance--now I'll have to build it for real and see if it sounds as good as it looks.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=141025&highlight=
Click to expand...


That sure sounds good.


I have read this whole big thread. I did seem to get a concensus that somewhere between 17 and say 22 MA might be best.

Now, to bring this full circle, could the "Grounded Grid preamp be reoriented to be anode driven as opposed to being Cathode driven? Now, I'm a real newbie here, so if I understand rightly, the anode is the plate? As anyone explored that idea?

Ray Bronk
 
#769
Ray, The best place for you to start might be by building Rosenblats Grounded Grid in kit form. This will teach you the basics. You can then experiment and modify from there.

For those that were curious about my 12B4 line stage I powered it with an Eico High Voltage tube regulated variable supply. That supply fed the a pair of local 0D3 gas regulators for each channel. A seperate lab grade variable DC supply powered the filaments. I will complete mine soon but with a more practical tube regulated supply... but still will feed the local gas regulators as well. They do make an audible positive difference and who can resist the purple glow! I've absolutely no interest in adding the phono stage at my end. I got out of the LP end of things a number of years back... Really good LP playback gear is too $$ wasteful.

Mark
 
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#770
Mark Allen said:
Ray, The best place for you to start might be by building Rosenblats Grounded Grid in kit form. This will teach you the basics. You can then experiment and modify from there.

For those that were curious about my 12B4 line stage I powered it with an Eico High Voltage tube regulated variable supply. That supply fed the a pair of local 0D3 gas regulators for each channel. A seperate lab grade variable DC supply powered the filaments. I will complete mine soon but with a more practical tube regulated supply... but still will feed the local gas regulators as well. They do make an audible positive difference and who can resist the purple glow! I've absolutely no interest in adding the phono stage at my end. I got out of the LP end of things a number of years back... Really good LP playback gear is too $$ wasteful.

Mark
Click to expand...



Hi Mark,

\i seem to recall somewhere in this thread, someone had posted a schematic showing tube rectification along with the 12B4.

\yeah, \i thought about building his preamp, but \i'd rather build something that will sound better and presumably cost less to build than Bruce's GG. Besides, \i was kicked off his board for "socializing" like asking for help with parts layout. Being blind is tough enough, and \i think what really pissed him off is when \i challenged anyone on that forum to close there eyes and see if they can solder anything. Well, \i did eventually hear someone's homebrew GG, and well, it was ok. \i could \i guess live with it, even though my TVC had better resolution, but not that tube magic. So that's why i want to build the 12B4. Thanks for letting me rant just a bit.

Ray Bronk
 
#771
12B4 Line Stage + Phono FINALLY POSTED!

Well it's up on my website now, only 2 months after I promised it:
http://www.audiovib.net/Designs/Audio/12B4/phonostage.htm

and the listening tests are posted on my Blog:
http://audiovib.blogspot.com/2009/09/12b4-line-12ax7-phono-stage-blind-test.html

And the specs for the Step-up transformers are posted at:
http://www.audiovib.com/Parts/Xfrmr&Chokes/PhonoStepUp71107A.htm

WHEW!

I think it will answer some of the questions below on layout, parts, and there are 3 optional power supplies in the design.

Cheers
 
#772
Besides, \i was kicked off his board for "socializing" like asking for help with parts layout.
Click to expand...

Man, I think thats a pathetic response from a designer to someone who was truely interested in building his preamp! If he didn't want folks building them on their own then why did he publish a book encouraging people to do so with it's schematic and circuit description in the first place? I have one of those books around here somewhere... I built mine from that book! Makes me want to cancel his newsletter and this also leads me to believe why there is now an apparently very decent version of the GG available from China for 79 bucks plus shipping... dale resistors, WIMA capacitors and all.

At any rate, I agree the 12B4 in just about any of it's gestations is far superior to the GG.

Mark
 
#773
So the only real difference between my version and yours is more or less the choke vs. CSS. I have access to quite a few different surplus chokes locally but to be clear on it... what make, model 150 h choke do you reccomend as being of super high quality or should I say of very high sonic quality? Surplus chokes are an unknown as for sonics, perhaps better and perhaps not so I need a starting point that you reccomend. I'd like to round up our old group to do a listening comparison of Choke vs. CSS to hear what the differences are before we finish a number of 12B4s we started constructing back before Digital Cinema disrupted my life...

Also, have you tried bypassing your output cap with a smaller cap? I did this and although I am using very high grade 5uf Multicaps on the output there was a noticable improvement when I added a .01 Infinicap. I have also bypassed the OD3s with an Infinicap SETI to qwell any noise, and those gas toobes can be somewhat noisy!!

Have you also considered trying the Wright shunt regulator in place of the 0D3s? I was told it will give far superior performance over the gas toobes... I started one but never finished it... might still give it a go though as a number of folks on this thread highly reccomended it over the gas toobes for both sound and stability.

Thanks!
Mark
 
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#775
Hi Zen,

Thats exactly what I intend on doing. We already tested one German built HV power supply aside from the gas toobes, gas toobes beat it hands down. There are alot of very good claims for the Wright Regulator and it is a very costly circuit to build and it is very parts specific for it to even work properly. I rummaged up the old Wright Regulator board group buy to see of any boards might still be available. One thing is for sure... The Wright Regulator is boreing compared to the wonderful glow those gas toobes give off!!! But nice glow doesn't correlate to good sound quality... I think even if the Wright Regulator does sound better I'm still going to have to keep those gas toobes lit up just for the romantic looks...

Can you say Wright Regulator 10 times really fast? Its pretty dififcult!

Mark
 
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#776
Mark Allen said:
So the only real difference between my version and yours is more or less the choke vs. CSS. I have access to quite a few different surplus chokes locally but to be clear on it... what make, model 150 h choke do you reccomend as being of super high quality or should I say of very high sonic quality? Surplus chokes are an unknown as for sonics, perhaps better and perhaps not so I need a starting point that you reccomend. I'd like to round up our old group to do a listening comparison of Choke vs. CSS to hear what the differences are before we finish a number of 12B4s we started constructing back before Digital Cinema disrupted my life...

Also, have you tried bypassing your output cap with a smaller cap? I did this and although I am using very high grade 5uf Multicaps on the output there was a noticable improvement when I added a .01 Infinicap. I have also bypassed the OD3s with an Infinicap SETI to qwell any noise, and those gas toobes can be somewhat noisy!!

Have you also considered trying the Wright shunt regulator in place of the 0D3s? I was told it will give far superior performance over the gas toobes... I started one but never finished it... might still give it a go though as a number of folks on this thread highly reccomended it over the gas toobes for both sound and stability.

Thanks!
Mark
Click to expand...

The chokes I'm using are made for me in Hong Kong by a botique winder I got to know a few years back in my travels. There are two versions--cheap (C-Core) and expensive (R-Core). I'm using the cheap chokes and very pleased with the sound. I'm going to get some of the R-Cores and try them out as soon as I can afford another buy.

I have done Choke vs CCS listening tests, and I prefer the choke sound--it seems quicker and more alive. YMMV, but I expect it is related to the old feedback vs linear issue. A CCS is a feedback device, and it seems to my ear that feedback always squashes the harmonics--no matter where in the circuit you put it.

Bypassing the output cap is a great idea--I've been meaning to do that one of these days, but now with your reminder, I'll going to do it. You are using a 1/500 ratio, I think I'll try 1/100 ratio. Also, bypassing 0D3 is a good idea--use about .1uF??
 
#777
Mark Allen said:
Hi Zen,

Thats exactly what I intend on doing. We already tested one German built HV power supply aside from the gas toobes, gas toobes beat it hands down. There are alot of very good claims for the Wright Regulator and it is a very costly circuit to build and it is very parts specific for it to even work properly. I rummaged up the old Wright Regulator board group buy to see of any boards might still be available. One thing is for sure... The Wright Regulator is boreing compared to the wonderful glow those gas toobes give off!!! But nice glow doesn't correlate to good sound quality... I think even if the Wright Regulator does sound better I'm still going to have to keep those gas toobes lit up just for the romantic looks...

Can you say Wright Regulator 10 times really fast? Its pretty dififcult!

Mark
Click to expand...

I have to agree. Problems aside, I just like the sound of simple gas tube regulators over other solutions. I do think that they work best with PI filtered power supply as the PI filter supplies an instantaneous resivoir from the Choke field. Tim Par.....??? of EAR is a big fan of simple power supplies as well. I know he builds and sells both, but in one of his interviews he mentioned that the simple C/E core transformer and PI filter gave better sound than regulated power supply. I think that the main advantage of tube regulation is that it just acts like another section or two of PI filter, but without the varible voltage drop.
 
#778
On the output caps the Multi-Caps don't need quite so much bypassing. Group listening tests are how I ended up with such a hi ratio. The type of capacitor (brand) used is also very important. I've long been a Multicap fan but they don't necessarily work in all situations although they want you to think they have one version for each circumstance. When it comes to bypassing them remember these are already multiple caps in parallel in one package. I'm bypassed on the 0D3s at .22uf right now... haven't yet experiemted there or looked at noise content yet, Digital Cinema interupted my life right at this point of the project. Boards ordered for the Wright Shunt Regulator so we shall see.. er hear whats up there.

Please post when you have a couple of chokes in stock that I can purchase... Am most anxious to try those.

Mark
 
#779
Hi,

coffeedj said:
I have to agree. Problems aside, I just like the sound of simple gas tube regulators over other solutions. I do think that they work best with PI filtered power supply as the PI filter supplies an instantaneous resivoir from the Choke field. Tim Par.....??? of EAR is a big fan of simple power supplies as well. I know he builds and sells both, but in one of his interviews he mentioned that the simple C/E core transformer and PI filter gave better sound than regulated power supply. I think that the main advantage of tube regulation is that it just acts like another section or two of PI filter, but without the varible voltage drop.
Click to expand...

Why use the OD3?
Of all the voltage regulator valves I'm familiar with it's about the only one that's really noisey.

Cheers, 😉
 
#780
CCS and choke load Rk-calculation

Hi,
I went through whole 78 pages, lot of knowledge about 12B4.
I would like to try this very tube in two configuration with CCS load (Ixys chip) and choke load (150H/50mA/700R). The power supply which I already have from pervious preamp is able to deliver 160V DC (B+).
Form plate characteristics seems that Ia=100V, Vs=-12V Ia= 20mA is linear enough. Simple Rk calculation gives Rk=600R but this is true for resistive load. Unfortunately I have no experience with CCS and choke load. So de question is does Rk is calculated properly if not how to do that..
Any help would be highly appreciated..
 
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