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

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P

pengboon

Member
Joined 2005
OK, I did a little more searching.

What if I had a switch to ssitch between the RCAs and puttingthe preamp signal to another gain stage of say 5687, single triode or push-pull like the attached schematic. Any views/inputs on this?
 

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Zen Mod

Zen Mod

Official Court Jester
Joined 2003
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LuckyLyndy said:
Amperex,
I would like to hear your preamp.

Just a quick note here. Choky, I am sorry, but I couldn't discern any difference between the solid state regulated power supply vs. your
gas shunt one.
Mark differed, and felt the gas had a better sound. If looks count, yes, the purple glow off those things was pretty dramatic in a darkened room. But I think I am going ahead with the solid state when I build mine.
Lyndon
Click to expand...


hehe....to each his own.....
most important thing is that we are here to help each other.....
shunt or series,SS or tube-it's a matter of taste,but only when reg is good enough;
I'm glad that you have that "good enough" ;)
 
M

Mark A. Gulbrandsen

Member
Joined 2001
Arnold C,

I moved my Gas Regs right up with the line stage as Choky reccomended and literally connected the two chassis together. I also added some .22 Wonder caps across the output of each VR-150. Now the difference is very obvious with great improvement in macro detail and noticable improvement in the soundstage who's width and depth has improved very noticably. Any graininess and other artifacts have pretty much disapprared all together. Overall It would be difficult to get me to switch back to the solid state reg again. I have to say that Choky, Fedgrove, and others that prodded me to try the shunt type regs are right on the money as to shunt type being better sounding.

Mark
 
Zen Mod

Zen Mod

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Mark A. Gulbrandsen said:
Arnold C,

I moved my Gas Regs right up with the line stage as Choky reccomended and literally connected the two chassis together. I also added some .22 Wonder caps across the output of each VR-150.....................
Mark
Click to expand...


Mark-be carefull -you are right at the edge with .22 in parallel with gas toobz;

disconnect them and listen -if sound is worse,start with some smaller caps in parallel,starting in nano range......say-4n7 upwards;
stop when you stop to hear improvement
 
Zen Mod

Zen Mod

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Mark A. Gulbrandsen said:


Limit of what? How come I'm right at the limit? What is the lmiit and why? The toobes seem to be ok with it. There is also a 35mf at the dc input of one channel of the line stage. I was going to add one to the other channel but I didn't have an extra in the parts bin.....

Mark
Click to expand...


when you put cap in parallel with gas stab,you'll likely have sawtooth oscillator
that's why I never take risk of putting any capacity there.
in any case- you'll find that (critical) data only in some tube books and just for some gas stabs. usually none capacity is mentioned,meaning that you can't use any cap there

few nano (maximum) are just for golden eared:devilr:
I'm not the one

edit:
you can put zillion microfarads before series resistor (that one preceding gas toob)........but across gas toob ........nada,zilch,none.......;)
 
S

snoopyma

Member
Joined 2004
12B4A Cathode Follower (CF)

I read with interests the concept of 12B4A liine stage using LM317 ccs at the cathode.

I want to build a two-stage line stage having the output stage of using 12B4A as cathode follower. My preliminary idea of this cf stage is:

(a) Shunt regulated B+ of 175 volt to the plate of 12B4A;

(b) LM317 current regulated using 48 ohm resistor (25ma) connected between its cathode and ground with 220uf (+.1uf) bypass cap;

(c) the grid tied to ground with 1M ohm resistor.

Does this work? Is this so simple?

I don't know how to figure out the reistance of the LM317 ccs and the grid voltage here. Do I need to put another resistor between the LM317 ccs (317 with 48 ohm reisstor) and ground in order to bias the 12B4A correctly.

Any help and suggestion is appreciated. Thanks.
 
M

Mark A. Gulbrandsen

Member
Joined 2001
Mark, how close are your VR tubes to the 12B4?
Click to expand...

They're about three inches away bywire and two inches away by measuring tape. So far no problem with the .22's caps at all. I will probably lower them to .01 though...will pick up parts tommrrow. I can see how it wopuld cause a sawtooth when the tubes igniote and the cap takes the charge ... and so on and so forth.

Mark
 
Shoog

Shoog

Member
Joined 2002
"...using 12B4A as cathode follower."

Cathode followers are generally considered to be worse sounding than an anode follower. This is because they have 100% degenerative feedback which tends to rob the sound of air, punch and life in general. It might be better to use a very low resistance triode instead, as an anode follower. This will achieve most of the benefits of a cathode follower without the feedback.

Shoog
 
S

snoopyma

Member
Joined 2004
Shoog said:
"...using 12B4A as cathode follower."

Cathode followers are generally considered to be worse sounding than an anode follower. This is because they have 100% degenerative feedback which tends to rob the sound of air, punch and life in general. It might be better to use a very low resistance triode instead, as an anode follower. This will achieve most of the benefits of a cathode follower without the feedback.

Shoog
Click to expand...


Hi Shoog,

Thanks for your reply. I am currently using single WE437a (almost the lowest resistance triode that I can find with a suitable amplification factor) WOT (lundahl) line stage with Allen Wright's SuperReg (shunt type) p.s. I want to try another approach (tube if possible). As I am using horn speaker system of double 15" woofers per side, I need a line stage (preferably tube one) with as low output impedence as possible to drive them to outstanding dynamics and speed. Besides, the line stage has to drive 25' long cable too.

As far as I know, the output impedence of a cf is gm*u/(1+u), so the 12B4a as a cf can deliver a 130 ohm output output impedance, which is really good to me.

Though there are many sayings that the cf is not good, I have listened to a few good line amp. using cf as output stage that are sounding good. I also hope that the LM317 ccs can improve the 12B4a cf.

So I will try. I hope it can work. Thanks.
 
Shoog

Shoog

Member
Joined 2002
If you are familiar with Allan Wrights Super Regs and are experienced enough to try something a little bit more complex, why not go for the SLCF. This has all the benefits of a CF, but takes out the feedback element. I have built a buffer based on this and also am currently using a line amp with a PCC88 front end and a SLCF back end. This gives gain and super low output impedence.

Shoog
 
S

snoopyma

Member
Joined 2004
Shoog said:
If you are familiar with Allan Wrights Super Regs and are experienced enough to try something a little bit more complex, why not go for the SLCF. This has all the benefits of a CF, but takes out the feedback element. I have built a buffer based on this and also am currently using a line amp with a PCC88 front end and a SLCF back end. This gives gain and super low output impedence.

Shoog
Click to expand...


Hi Shoog,

Thank you for your advice again. I am interested in Allen's SLCF too, but I find it a little bit more complex. I would like to comment that the ECC88 or WE417a is irreasonably expensive.

I consider that the output stage using 12B4A with LM317 ccs at cathode as a CF is simple enough. If it works properly, I may connect its output to a high quality 4:1 output transformer (without DC) via. a 4uf capacitor. This will further lower the impedance by a factor of 1/16. This is similar to a parafeed line stage but this time the output is taken from the cathode instead of the plate. This is what I am thinking and what I want to try. Please correct me if I am wrong.

Thanks.
 
M

Mark A. Gulbrandsen

Member
Joined 2001
Well, the VR-150's are so cheap that splitting it into dual mono just makes sense. The double pair does draw a bit more standing juice from the mian supply but my main supply is large enough to handle it..... Several folks have heard it since I moved the reg toobes closer to the line stage and all are pretty much in agreement.... Sounds fantastic!

I am also going to try the 7233 tube which has a 230 ohm plate resistance! Thats about as low as it gets in toobes......

Mark
 
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