251 schematic with 6S6B-v triode, launching the project.

[Papa Tango Charly]

Hello, Here is my new schematic for C12 with a 6S6B-V i will probably use the original Apex 460 transformer + capsule C12 "CTS3 omni from taskar".sold buy Vami.
Tbone Black PSU.
Do you have any suggestions, or advises?
I was wondering if C4 1uf would be a good choice for the 6S6B-V
Thank you all for your cooperation!

 

[Drosselmeier]

R9 = 10 K

 

[Khron]

And you might want to add a 100n or so from the R4/R5/R6 node to ground.

PS. Looks way more like a 251 schematic than a C12, between the self-bias and the 100p coming off the plate.

PS2. And who is this "we" that are "launching the project"?

 

[Papa Tango Charly]

Hello guys thank you for your help I have 3 x 6S6B- V we are building 2 mics with a good friend in the old Apex 460 body’s We are about to build the pcb.

R9 = 10 K

Is 10k the original value? Not 10M? what will it change. TK best

And you might want to add a 100n or so from the R4/R5/R6 node to ground.

What will it change can you show where to place it. TK best

 

[Khron]

can you show where to place it.

from the R4/R5/R6 node to ground.

How much clearer of a description do you need? Or if even that's not clear enough, should you even be poking around dangerous-voltage circuits in the first place?

Is 10k the original value? Not 10M? what will it change.

Well, 10 MEGOHMS in series with the tube supply won't leave any voltage for the tube. Ohm's law, anyone? How did you arrive at that value, anyway?

 

[Papa Tango Charly]

How much clearer of a description do you need? Or if even that's not clear enough, should you even be poking around dangerous-voltage circuits in the first place?

Thank you for your concern Khron. That’s why I’m not doing it alone my friend is an engineer .
So the 100nf should be place after R6 before the ground right? Does the value of the condo has a impact on the sound. i can't see this condo on the original Schematic.

Well, 10 MEGOHMS in series with the tube supply won't leave any voltage for the tube. Ohm's law, anyone? How did you arrive at that value, anyway?

thank you

We are about to build the PCB there might be some mistake we need somme help.

 

[Khron]

We have made our schematic base on this schematic that uses a 6072A.

Ok, i see an R10 there, but with no value. How did you decide that should be 10 megohms?

And what makes that a "C12" (as i've already asked)?

So the 100nf should be place after R6 before the ground right?

How about putting that on the schematic you already have, to minimize the chance of verbal misunderstandings?

 

[Papa Tango Charly]

OK i Will do That.
This is the only Selfbias C12 version i found on internet. i can build it with a simple Tbone PSU. That why i choose this schematic. Thank you

 

[Khron]

This is the only Selfbias C12 version i found on internet.

Then "technically" it's not a "C12", is it? Maybe C12A, but without a nuvistor... That, plus that 100pF between plate and ground is why i said

PS. Looks way more like a 251 schematic than a C12, between the self-bias and the 100p coming off the plate.

Kinda like putting a Ferrari engine into a Jaguar and calling it a Chevrolet Corvette... It's still good, sure, but definitely not what it says "on the label"

 

[Papa Tango Charly]

Then "technically" it's not a "C12", is it? Maybe C12A, but without a nuvistor... That, plus that 100pF between plate and ground is why i said

Ok I changed the name of the topic of the thread . I'm going to learn to tweak Eagles and send you the fallowing changes on the initial schematic.

Any advises, comments are welcome. Best

 

[Khron]

I'm going to learn to tweak Eagles and send you the fallowing changes on the initial schematic.

And you might want to add a 100n or so from the R4/R5/R6 node to ground.

Have fun applying 120V to the front half of your capsule then...


PS: Just so you can't say i'm not trying to help - https://sound-au.com/beginners.htm#s80

 

[rock soderstrom]

Hello guys thank you for your help I have 3 x 6S6B- V we are building 2 mics with a good friend in the old Apex 460 body’s We are about to build the pcb.

You don't actually need a new PCB, everything is already there. You can build your new circuit on the existing board with very few changes. You don't even have to cut traces, I've just done this with a T.bone SCT700, which has the same core circuitry.

I call the whole thing EASYMOD M251, I will publish the project soon.

The idea behind the mod is to keep the effort as low as possible, it's really very simple, you don't even have to open the PSU.

 

[Papa Tango Charly]

That sounds great Rock thank you. can't wait to hear from it!

Have fun applying 120V to the front half of your capsule then...

I don't undersand your comments? Have i placed the 100nf at the wrong place? where should i place this condenser? 120V will kill my capsule what are you trying to say? can you be more specific please. Thank you

 

[Khron]

I don't undersand your comments? Have i placed the 100nf at the wrong place? where should i place this condenser?

And you might want to add a 100n or so from the R4/R5/R6 node to ground.

If you can't notice, you placed that capacitor between R6 and ground (in series with R6 - have i said anything about that, anywhere?).

Do you see / have any connection to R5 and R5, from the non-grounded terminal of that capacitor?

And please, read through that article i linked:

PS: Just so you can't say i'm not trying to help - https://sound-au.com/beginners.htm#s80

Spoilers: R4 and R6 are supposed to form a (DC) voltage divider...

 

[Mr. Moscode]

The size of C4 has nothing to do with the tube. It depends on the impedance or resistance to ground of the load on the other side of it. That will determine the low frequency cutoff of the circuit. Post the rest of the circuit, please.

 

[rock soderstrom]

I was wondering if C4 1uf would be a good choice for the 6S6B-V

The size of C4 has nothing to do with the tube. It depends on the impedance or resistance to ground of the load on the other side of it.

That is correct, the load on the secondary side of the transformer is relevant for the calculation of the coupling capacitor C4.

it is f=1/(2PiRC) for the calculation of the lower cut-off frequency (-3dB), with a 200R output impedance of the microphone with a 11.6 to 1 transformer* and a 1uF capacitor, the lower cut-off frequency is about 6Hz.

I would not increase the capacitor size (the stock transformer is not the biggest)

*if it is the same transformer as in the t.bone SCT700
with a 6.5 to 1 transformer the lower end of the bandwith is at around19Hz