Finished AKG C12 clone pics

[bezen4uk]

Another fixed bias idea (tab-funkenwerk copyright):
http://www.tab-funkenwerk.com/id85.html

Regarding cathode vs fixed biasing:
*cathode biasing is good for DC stability of tube but introduce phase shift at LF and increases Rout;
*fixed biasing hasn't these limitations but may need tube matching, better PSU stability etc.

 

[e.oelberg]

I built two Elam 251 clones with CT12 capsules, they sound fantastic, finally i settled with telefunken ecc801s tubes instead of 6072

 

[david-p]

I built two Elam 251 clones with CT12 capsules, they sound fantastic, finally i settled with telefunken ecc801s tubes instead of 6072

Did you use ECC801S and why did you not use 6702?  Are the two triodes in parallel, or did you ground one side, as in the Elam251 circuit?  What transformer do you use?

Thanks for answers to these questions,.

David

 

[saxmonster]

Would love to build a 251, gonna be my new project.  Ok I guess i should find a Schematic first.  Anyone have info they can email me?

-Scott

 

[telefunk]

Would love to build a 251, gonna be my new project.  Ok I guess i should find a Schematic first.  Anyone have info they can email me?

-Scott

Try google images. "ela m251 schematic".

 

[grantlack]

Did you use ECC801S and why did you not use 6702?

i'm considering the same substitution based on the quality vs. price ratio of what's available.  on a good day you could probably get 4 of these for the price of one GE 5-star, and of course not every tube is mic-worthy so a sample pool is nice.  i've read good things about the majority of these living up to their low-noise spec though.  8)

Anyone have info they can email me?

Try google

this sort of stuff really is out there. we promise!

 

[e.oelberg]

I built two Elam 251 clones with CT12 capsules, they sound fantastic, finally i settled with telefunken ecc801s tubes instead of 6072

Did you use ECC801S and why did you not use 6702?  Are the two triodes in parallel, or did you ground one side, as in the Elam251 circuit?  What transformer do you use?

the ecc801s sounds to my ears a bit more open an natural, the 6072 on the other side is more in you face, a bit rough. Also great, probably even better for voice recordings in context of a mix, while the ecc801 is probably better for averything else

 

[david-p]

I built two Elam 251 clones with CT12 capsules, they sound fantastic, finally i settled with telefunken ecc801s tubes instead of 6072

Did you use ECC801S and why did you not use 6702?  Are the two triodes in parallel, or did you ground one side, as in the Elam251 circuit?  What transformer do you use?

the ecc801s sounds to my ears a bit more open an natural, the 6072 on the other side is more in you face, a bit rough. Also great, probably even better for voice recordings in context of a mix, while the ecc801 is probably better for averything else

Thanks!  I'll try one on your recommendation.

 

[gyraf]

A problem with the GE 5-star is that there is a very good chance that the batch of tubes you get hold on has already been tested and rejected for microphone use (by someone else).

Jakob E.

 

[david-p]

A problem with the GE 5-star is that there is a very good chance that the batch of tubes you get hold on has already been tested and rejected for microphone use (by someone else).

Jakob E.

Are all new Electro Harmonix 12AY7/6072a tubes also a waste of time and money for microphone use?

David

 

[MagnetoSound]

Are all new Electro Harmonix 12AY7/6072a tubes also a waste of time and money for microphone use?

EH don't manufacture. Where are they sourcing them now, I haven't kept up. A few years ago they were primarily just re-screening Sovteks for most of their line, although I think a few China tubes may have crept in, in some instances. Do they QC them better now? Maybe, but then they might be moving greater quantity, so perhaps not ...

Somehow I doubt they will have anything to rival the likes of GE, RCA et al from back when.

 

[david-p]

In what way do EH valves not meet the 6072a specification?

David

 

[MagnetoSound]

They might meet the spec. They might struggle to pass selection for noise and microphony.

 

[david-p]

They might meet the spec. They might struggle to pass selection for noise and microphony.

Are low noise and microphonics not part of the spec?  Are they just a question of luck?



David

 

[telefunk]

In what way do EH valves not meet the 6072a specification?

David

EH 6072A's are basically Russian made Sovteks.

And contrary to the common myth around the net, they usually do sound really good and have better microphonics and noise than many GE 5-stars, mostly due to the reason Jakob already mentioned above. But go and ask somebody who sells those GE's and you'll surely get a different answer. Just buy 10 EH's and choose the best and it's going to be a great 6072a.

But also, if you are lucky to find a really good GE, it's going to be a nice sounding tube for sure.

 

[MagnetoSound]

Oh ... I'm stuck in the past! That figures.  ;D ;D ;D

 

[gyraf]

They might meet the spec. They might struggle to pass selection for noise and microphony.

Are low noise and microphonics not part of the spec?  Are they just a question of luck?

Low noise and microphonics, when used in a very high grid resistance circuit like mics, is unfortunately not part of the specs a new-production tube aims to meet. Remember, we use these waaaay out of specified range, and hope for a tube design/build that'll be forgiving when pushed like this.

Jakob E.

 

[robovox]

Thanks for putting this in context so succinctly, Jakob.

 

[bezen4uk]

Hi,
Tubes have getter (silver-color coating) that adsorbs residual tube gases at relatively high temperature. Old tubes  may have high gas content and need some temperature treatment.

Most tube mic circuits run tubes in relatively cold mode. For example: EC92 in UM57 mic has 75V*0.9mA, but EC92 nominal  anode rating is 250V*10.5mA or 40 times higher! Heater is colder than nominal too (about 15% less power). I think the getter can't be activated in typical mic modes.

When I have noise issues with NOS or old tubes, I make thermo treatment. Usually I run the  tube for 20 hours at NOMINAL POWER RATINGS. Though, it doesn't help always.

 

[dmp]

Low noise and microphonics, when used in a very high grid resistance circuit like mics, is unfortunately not part of the specs a new-production tube aims to meet. Remember, we use these waaaay out of specified range, and hope for a tube design/build that'll be forgiving when pushed like this.

Jakob E.

The current manufacturing target is tube amps. i.e. the magic of a 12ay7 in tweed type amps, yes?
Is the operating point & grid resistance different in those designs? I guess I don't understand how it is different.
I'm very curious as I've built a few tube mics and want to start playing with a original design...