• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    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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#282
If this 12B4a preamp was hooked up to a current output DAC (like Monica2), will it work well? I read somewhere that this type of DAC prefers a lower input impedance, like the GG design? So I need a I/V resistor that will solve the problem?

thanks!
 
#283
Shoog said:
Just a simple question. I am toying with the idea of building a 12B4 preamp. I have some big light ballast tranformers which I would like to try as plate chokes. I expect them to be good down to at least 400hz. The question is could I put a simple single transistor CCS before the choke (ie +B - CCS - CHOKE - PLATE) to take up the slack.

Shoog
Click to expand...

Uhhh,

What do you think what’s left from the inductance when biased with the DC anode current? These ballasts are not designed for DC bias and probably driven into saturation right away.

Cheers 😉
 
#285
4 channel Pre

Hi

I'm thinking of making a 4 channel preamp after my behringer dcx 2496. I have baypassed the analog section like this:
An externally hosted image should be here but it was not working when we last tested it.

As it is now, i run the signal directly into my 6 deck pot(I use only 4), and directly to each amp. The pot is 20k.
Would the 12B4 circuit have any problems matching the DACs (AKM 4393) output? Shold the pot be placed before or after the 12B4?

Cheers
bjorn
 
#286
Mark A. Gulbrandsen said:


You need a voltage output type DAC and then it'll work fine. HGo back and look for BRian BEck's schematic in this thread. Thats exactly what he's using this line stage for!!

Mark
Click to expand...

Ok, gotcha.

Brian,
Can you show me how do you compute the values of R10, R21, L1 and C3? Would this values be applicable to Monica2?

thanks! 🙂
 
#287
Single or dual CCS?

Hello,
My first time posting although have been reading for a while. I am building a 12b4 pre. Does anyone know if when using a CCS at the cathode it is best to have be one CCS for each tube or just one shared CCS for both tubes?
Tom
 
#288
Hey,

Mark, you haved try the RNT-400 from thiel in combination with a DC load from your powersupply, can I see 🙂

Have you try it with a 220Vac load?
I wonder if the noise floor is still low, if it would be an option for me as a supply on my 12b4a preamp.

Venlig hilsen Jan Jensen
 
#290
Re: Single or dual CCS?

BGcap said:
Hello,
My first time posting although have been reading for a while. I am building a 12b4 pre. Does anyone know if when using a CCS at the cathode it is best to have be one CCS for each tube or just one shared CCS for both tubes?
Tom
Click to expand...

HI BGcap

Welcome! You must use one CCS for each cathode. Circuits with two cathodes sharing one CCS have an other function, namely phase inversion to drive PP stages.

Erik
 
#292
Mark A. Gulbrandsen said:
Update!

I got it working on just one channel tonight but I did get them glowing. I need to get different resistors tommrrow at the parts store. Note the wrong basing at this site This was my problem. Should have been labeled pin 5.... not pin 4... there is not even a 4th pin on these tubes bases....
Click to expand...

yup; wrong pinout
just go to Duncan's and download tdslpe..........
if you didn't already........


did you listen that solo channel?
:devilr:
 

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#294
I saw some schematics here that use capacitor input and some choke input. For this particular tube (12B4), I'd like to hear the experiences and opinions as to the differences between these 2. I'm in the process of plannign a simple 12B4 preamp and am deciding on the secondary voltage of the power transformer. I already have a 5H 150mA (DCR <100ohms) choke from a previous project to use, and a 15uf motor run, and various 'lytics that I can use. I will be driving a EL84 PP with it, and will probably go with the LM317 on the cathode.

Pls advice, thanks! 🙂
 
#297
Thanks Arnoldc for your inputs. This thread has gotten very long, and when I searched, it doesn't tell me the page where the search string is found, so it's pretty tedious to go through all the pages... :xeye: Is your PSU on post #230?

another thing, can I actually use this as a headphone amp as well, what modifications do I require to make this happen?

thanks!
 
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