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    Building, troubleshooting and testing of these amplifiers should only be
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12B4 Preamp

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Salas

Salas

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12B4s are not dead tubes to impact. But from what I saw in threads, people don't usually mention. But they have great Mu for modern preamp gain needs and great sound. Don't you like the sonic results of what you got now? Is it quiet for self noise? Is it less microphonic than before? If yes, you made yourself one of the best preamps there is to make before entering exotic DHT land (much more microphonic), and it behaves normally.
 
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ray bronk

Member
Joined 2005
Salas said:
12B4s are not dead tubes to impact. But from what I saw in threads, people don't usually mention. But they have great Mu for modern preamp gain needs and great sound. Don't you like the sonic results of what you got now? Is it quiet for self noise? Is it less microphonic than before? If yes, you made yourself one of the best preamps there is to make before entering exotic DHT land (much more microphonic), and it behaves normally.
Click to expand...

Hi, i have read this thread and the real biggy thread discussing various aproaches to the 12B4 preamp. From what I read, the power supply is everything with this preamp. It has to be as clean as possible to get the best sound. Also, it seems that a roughly 17MA to say 22MA seems to be about right for this tube. Some will question this and say the 30MA is the best. But reading all of the thread, the lower current rating seems best. You can also try a plate choke which is supposed to help too. A couple of people used gas tubes for regulation. That made a big difference too. So take it from there. I don't have the bucks to build one otherwise I would build it or have it built for me.

This thread is worth the read. If yours sounds good to you, then keep it. Maybe, some of the ideas presented in the thread can help to improve what you currently have.

http://www.diyaudio.com/forums/showthread.php?postid=771320#post771320

Ray Bronk
 
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ray bronk

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Joined 2005
philipbarrett said:
I have searched and read pretty much everything on diyAudio regarding 12B4 preamps & now my head is spinning!

I would like to build one but am looking for schematics for both the pre & a good PSU to match (I'm a bit partial to tube rectifiers but can be easily convinced). Many of the earlier posts no longer have the attachments so I'm sorta flapping in the breeze here. It seems as if fdegrove & arnoldc are on to something but some information seems to be missing.

Any help for this pseudo-newbie would be much appreciated.

Thanks in advance.
Click to expand...


Hi, Well, then you know that the power supply is everything with this preamp. The power has to be as clean as possible. As far as the microfonics of the tube, see if you can find some Philips Jan tubes. Because of the military construction, they aren't supposed to be as microfonic as some of the other tubes.

Ray Bronk
 
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casouza

Member
Joined 2003
Hi, just a safety warning: in a pseudo-choke input PS, the input cap (47 nF) sees HUGE AC spikes, about 3-4 times the average DC voltage. Use an AC rated cap that can withstand high ripple. A safe choice would be a brand new 600 V AC (or higher) paper in oil or polypropilene motor-run cap.
DO NOT use Mylar, ceramic or old, leaky, NOS oil caps, those caps heat up pretty quickly in this particular application.
I have had one NOS PIO USA-made cap bulge and get sizzling hot. Fortunately I noticed it before the fireworks started.
 
vgeorge

vgeorge

Member
Joined 2004
goldenview.gr
Just finished my 12b4 pre and like the sound a lot. Quite pleased for a first tube project!
Built in two chassis, one with all power supplies and the other with Sala' s simper simplistic reg, heaters regulators and the tube circuit.
Very silent only slightly microphonic. Maybe try more with tube decoupling from chassis would help.
 

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vgeorge

vgeorge

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Joined 2004
goldenview.gr
I used a 6.8K resistor for begining. Cathode 1.2k bypassed with a 1000 uF.
325V to simplistic shunt 280V B+, around 165V on the anode and I have 19V on the cathode resistor.
I am going to experiment with your final shematic of the gyrator, as soon as I get some more 9610. I burned one during the testing phase and I don' t have any more right now.
 
Salas

Salas

diyAudio Chief Moderator
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Maybe you will like the resistor more after all, has its merit too. When you check with the gyrator, make sure to keep levels the same for comparing, its gonna up the gain. In what system did you listen to it by now? Any comparison preamps around?
 
vgeorge

vgeorge

Member
Joined 2004
goldenview.gr
My system now is horn loaded - based on Lynn Olson ideas - around 105db sensitivity with my F5 clone, that I just set up and try to configure crossovers etc, so I can not be sure. Your phono also. What I know is that music is much more alive and real maybe than with a passive pot previously used. Even if gain was enough before, F5 needs an active pre for sure.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
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This 12B4 with the simplistic Reg will be hard to beat in the future. One of the best things you could add to drive the F5. See for best mechanical decoupling of your 12B4s since you got ''real'' speakers, and you are mainly set.
 
vgeorge

vgeorge

Member
Joined 2004
goldenview.gr
I am thinking for a suspened suchassis for the tubes. Also add some dumping to the case. It' s a Hammond aluminium one. As this was was the first thing I build with tubes I wanted to have some sound first and then deal with details as my confidence builds up.
You can have look at the speakers I am setting up.
 

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Salas

Salas

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The real McCoy I see.;) I am afraid that some active anode load (any type) by upping the gain and adding some of its hiss, may lead you back to the resistor, because with so sensitive speakers it may add some ''artificiality'' taste. But you will see for real, soon.
 
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ray bronk

Member
Joined 2005
Salas said:
The real McCoy I see.;) I am afraid that some active anode load (any type) by upping the gain and adding some of its hiss, may lead you back to the resistor, because with so sensitive speakers it may add some ''artificiality'' taste. But you will see for real, soon.
Click to expand...


Hi, Ok, so is the final schematic using LEDs or just a MOSFET? There is a manufacturer that I am attempting to convince to build these as in his regular lineup of preamps, to get him away from the standard 12AU7 tube preamp.

So can someone just email me the schematic with the list of parts, running at 15MA at 20V. Not wanting to do any experimenting, just want to build it and be done.

What can I expect the gain to be, and the output impedance to be. I would probably for the grid stoppers use 4K each to have a good value and also to deal with the ringing of any form of microphonics. I also would need the exact specs for the transformer. I was thinking of simply using a diode supply to keep the power supply somewhat simple. Want to build this in one box.

As an idea, people have used the LED for regulation. Why not just use another 12B4 tube. They are also supposed to be good regulators in there own right.

I myself can not see the pics, because I am blind. So building this piece would be a nice project. I will have to ask some assistance of you guys here and there, like what do you suggest for the layout chassis size and so on. What size ohmage of pot is suggested?etc. etc. etc.


Thanks guys for any assistance.

You can email me at raybronk@gmail.com


Ray Bronk
w
 
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ray bronk

Member
Joined 2005
To Build a 12B4 Preamplifier from scratch

Hi, Ok, so let me ask this then. In this thread there has been several, well, a couple of schematics for the 12B4. Ok, so which one do I use with the exact values so I will be doing 15MA and 20B. I have not seen any replies to my queries yet, so I will ask this also. If I use a Class D supply, what do I need then to have the supply see at its output, ... B+ filament of 12,? and what other parameters? I'm trying to see if I can make this as simple as possible without sacraficing the quality of sound produced by this preamp. So I just need the schematic and the details as to what the power supply needs to see. I thank you guys for any help at all. I hope I get a response soon.

Ray Bronk


I CAN MAKE THIS AS SIMPLE AS POSSIBLE WITHOUT SACIFRICING QUALITY.
Salas said:
The real McCoy I see.;) I am afraid that some active anode load (any type) by upping the gain and adding some of its hiss, may lead you back to the resistor, because with so sensitive speakers it may add some ''artificiality'' taste. But you will see for real, soon.
Click to expand...
 
R

ray bronk

Member
Joined 2005
Zen Mod said:
maybe this will help you :

12B4A preamp - DIYAudio.rs

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

edit: shunt reg is further down the thread , one per channel
Click to expand...

Ok, thanks. Since I am not able to see the schematic due to blindness, I will have to ask someone else to look at this. this is kinda why I had posted what I had posted earlier. I know this is simpler to build than a typical 12au7 preamp. I wanted to know what I need to do with reference to the power supply voltages and current. I think I will look for a Class D supply that can give me what I need, and supplement as far as the supply goes to make this sound really good. I will pass this along. Is this the same schematic that the guy from Grece built, or is this the one from Brian or Frank, ... or neither?

Ray Bronk
 
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