Measured VF14 characteristic

[Dylan W]

Thanks Moby,
i suppose that you've measured the temperature inside the mic, thus 75°c is high but bearable.
i'll leave the nuvistor for the moment, and hope that the tube will last for long...

Oliver Archut uses a big dropping resistor epoxied inside the body of the Lucas CS-4 (with RTV). This is supposed to raise the internal temperature of the mic. As I understand it, the idea is that the higher internal temperature with VF14, which is missing with other tubes, is part of the sound of the U 47.

Do you have evidence of this? From what I understand, there is no need for any kind of big dropping resistor in the CS-4.

I got it mixed up, it's "aluminum oxide cement."

http://lucasmicrophone.lefora.com/sreply/22855446/NEW-MICROPHONE-CONSTRUCTION

 

[o3misha]

Misha, but could you explain how you can achieve the cathode decoupling with a BV8 ?
Thanks

See UM57 or CMV563 schematic

 

[Melodeath00]

Thanks Moby,
i suppose that you've measured the temperature inside the mic, thus 75°c is high but bearable.
i'll leave the nuvistor for the moment, and hope that the tube will last for long...

Oliver Archut uses a big dropping resistor epoxied inside the body of the Lucas CS-4 (with RTV). This is supposed to raise the internal temperature of the mic. As I understand it, the idea is that the higher internal temperature with VF14, which is missing with other tubes, is part of the sound of the U 47.

Do you have evidence of this? From what I understand, there is no need for any kind of big dropping resistor in the CS-4.

I got it mixed up, it's "aluminum oxide cement."

http://lucasmicrophone.lefora.com/sreply/22855446/NEW-MICROPHONE-CONSTRUCTION

Very odd. Again, looking at the Lucas CS-4 schematic, I see no heater dropping resistor

 

[Moby]

Thanks Moby,
i suppose that you've measured the temperature inside the mic, thus 75°c is high but bearable.
i'll leave the nuvistor for the moment, and hope that the tube will last for long...

Oliver Archut uses a big dropping resistor epoxied inside the body of the Lucas CS-4 (with RTV). This is supposed to raise the internal temperature of the mic. As I understand it, the idea is that the higher internal temperature with VF14, which is missing with other tubes, is part of the sound of the U 47.

The heat inside U47 is not connected by VF14 anyhow. It's just a derivate of "burned voltage" needed for tube heating. U can achieve this temperature with any other tube even with the 6.3v types by putting the resistor in series with filament and increasing the voltage in PSU (if it's separated from anode voltage).

 

[granger.frederic]

Dear Misha,

i think that something is wrong with your schematic, or, i can't understand it ....!

in the AMI schematic, the output transformer seems to have a specific winding to put at ground potential, the AC coming from the cathode, thus decoupling it...

I doubt that the BV8 has been designed for that ...but maybe all that exceeds my knowledge ...

 

[o3misha]

There is just shield . Sometimes transformer has shield, sometimes not.  In my big badge old U47 bv8 transformer also has shield (brown contacts soldered to ground). Ami BV08 x-former has not got the shield the same as latest BV08 transformer, but it does not matter. You may use Black contact for DC filtering of the cathode accordingly to CMV563 schematic if you use self bias.

 

[granger.frederic]

ok Misha but could you please explain us the principle of that type of self bias....?
What becomes the AC coming from the cathode ...?
Why Oliver Archut gives two schematics: http://www.tab-funkenwerk.com/id69.html , for two different OT ..?

a little off topic but interesting....
thanks

Fred

 

[o3misha]

Just try this variant. The transformer is working as DC filter instead of capacitor. Sound is very different, but maybe you will like it. When I experimented with EF14 I tried this way, and it is very interesting.
About Tab Funkenwerk : Oliver made good modification, but the  mic  behavior is too far from original. Many people like it, but I prefer original sound, whithout extra cap in sound chain. My rule is : less components - better sound.

 

[granger.frederic]

I guess the AC cathode is added in the transformer primary, to the AC coming from the anode capacitor.
It's just a sort of positive feedback and i guess also why it sounds so different...

 

[Moby]

Dear Misha,

i think that something is wrong with your schematic, or, i can't understand it ....!

in the AMI schematic, the output transformer seems to have a specific winding to put at ground potential, the AC coming from the cathode, thus decoupling it...

I doubt that the BV8 has been designed for that ...but maybe all that exceeds my knowledge ...

As Misha already stated, yes, Bv08 fits here and yes, "specific winding" is nothing more than blind copper shield used mostly in non chambered Bv versions. Regarding cathode biasing, adding bypass cap will increase the gain thus it changes the sonic charachter. It also acts like a filter, so it adds phase shift in the low-low mid range. But it's possible that u will like that... It can sound "rounder"  or maybe "with more balls" (pardon my French )

 

[granger.frederic]

thanks moby,
i understand very well the principles of self biasing, but the decoupling with the output transformer is a bit vague for me ...
What's the advantage ?
is there side effects ...?

as i said before there must be a positive feedback in the primary, with probable comb filter effects....

 

[o3misha]

One more advise about EF14:  If you like this tube but don't like it's agressive highs, use Pio cap for C1 position. I personally prefer PIO caps in all positions : C1,C2 and C3 even with VF14. But IMHO, C1 is most important cap in sound chain, because this is first capacitor in signal chain from capsule to output .

 

[granger.frederic]

C1 is just a part of a HP filter to clean a bit the polarization voltage
it's not in the signal path, you could even remove it
same for C3
the most important is C2 and i already use a PIO.

 

[o3misha]

You are not agree again? Ok, forget about C1. 8)
Before something to argue, first ask yourself this question: Do I understand everything in the discussed aspect?
As signal is going through the c1, this cap influences on the sound. it works like input coupling cap. The signal from the capsule has very small amplitude, so the impact of the first capacitor is huge. I tested all types of modern capacitors, because I was curious. You are wrong, pal.  If you argue less and just tried what you advised you, you would have heard it all. I have created a topic about С1. 90% of people have heard the difference in sound polystyrol and PIO С1. Paper-oil capacitor gives a softer and more rounded sound at higher frequencies. For VF14 is not liked by everyone ( I like it, especially with mylar capsules), since this lamp itself sounds softly. But for EF 14, is another matter. The most important to get desirable sound from capsule before the tube will amplify it. For example, I believe that a ceramic capacitor С1 gives the sound excessive rigidity, and I long ago got rid of it.

 

[granger.frederic]

Dear Misha,
Please learn electronic basics before bashing !

C1 is not on the signal path.period.
It's a decoupling cap.If you remove it , the sound is still here and at worst you have some hum(depend on how the B+ is stiff).It forms an RC network and cleans the voltage polarization for the capsule.

Its effect on sound is really negligible (at least for humans...)

the only coupling cap in a U47 is C2.

There's sometimes a coupling cap before the grid ,like in a C12, and there, it can affect the sound.But in a U47 the capsule is connected direct on grid.

you say that C1 affects the sound in a U47,please explain us how or better: prove it.

that said, some people think that even the filtering caps in the psu can change the mic sound...
i disagree:for my poor little ears, it just add or remove some noise in the B+, depending on the quality/performance of these caps.
I read somewhere that someone who gave an advice on a fuse, achieved a better sound with that type of fuse ...etc...etc. The same with a silver PSU cable...bull sh*t !!!

things are quite simple in the electronic world, more with tubes, and my advices at all DIY'ers are:  think hard, than be logical, and experiment,make some notes and records, and the most important , trust anyone (including me),especially if he pretends to know everything on a subject

 

[o3misha]

Dear Misha,
Please learn electronic basics before bashing !

C1 is not on the signal path.period.
It's a decoupling cap.If you remove it , the sound is still here and at worst you have some hum(depend on how the B+ is stiff).It forms an RC network and cleans the voltage polarization for the capsule.

Its effect on sound is really negligible (at least for humans...)

the only coupling cap in a U47 is C2.

There's sometimes a coupling cap before the grid ,like in a C12, and there, it can affect the sound.But in a U47 the capsule is connected direct on grid.

you say that C1 affects the sound in a U47,please explain us how or better: prove it.

that said, some people think that even the filtering caps in the psu can change the mic sound...
i disagree:for my poor little ears, it just add or remove some noise in the B+, depending on the quality/performance of these caps.
I read somewhere that someone who gave an advice on a fuse, achieved a better sound with that type of fuse ...etc...etc. The same with a silver PSU cable...bull sh*t !!!

things are quite simple in the electronic world, more with tubes, and my advices at all DIY'ers are:  think hard, than be logical, and experiment,make some notes and records, and the most important , trust anyone (including me),especially if he pretends to know everything on a subject

C1 is the backplate grounding cap, 10nF. Yes, it forms a LPF with the polarising resistor R1, which is 100M. Corner freq is 0.2Hz. 
It is, however, directly in the audio path. Dielectric will affect audio quality. As far as small audio signal is going through this cap it affects on sound as first cap, before the  c2. Of course, c1 can not remove completely all agressive highs . But it also will help. I can't give you my ears, but I can say that many people can hear the difference. 
period...
How I can proove it? I tested two different c1 in one mic and asked people here on forum to listen two files with acoustic guitar in blind test.  You should learn the U47 schematic  I am not bashing, I ...Forget it. Remove your c1 at all, if you want. About PSU : if you don't hear the difference between different PSU or components in PSU you rather will not hear the difference between different types of c3 ( it is also filtering cap).

 

[ricardo]

I believe that a ceramic capacitor С1 gives the sound excessive rigidity, and I long ago got rid of it.

What type of ceramic capacitor did you get rid off?  There are many different types.  Some are better than polystyrenes, sliver mica & PIO .. especially for sound.

 

[o3misha]

It was original ceramic cap. Actually, I can't remember what exactly type of ceramic cap was in my mic.
I really doubt that ceramic cap is good for microphone with its harmonic distortion, but I beleave U that there is a good type . I love modern pio and piw caps more than any other type of caps because of its very smooth highs.

 

[ricardo]

I really doubt that ceramic cap is good for microphone with its harmonic distortion, but I beleave U that there is a good type .

NPO/CGO ceramics are the BEST caps if their size, value & voltage fit.  They have less distortion than practically ALL other caps.  Do do what caps are supposed to do and nothing else.

Have a look at Guru Scott Wurcer's 2 articles in Linear Audio to see how caps shape up for mike circuits.  He published more measurements in the Yahoo MicBuilders Group.

You  can easily check caps for eg microphony, without test gear.  Just your ears.

 

[o3misha]

It is very interesting for me, ricardo. Please, upload the link, I'd to learn more about different types of ceramic caps. Actually, I love Pio caps (modern,-not old!) because its non-leaner characteristic  I don't like too pure sound of polystirol or polypropilen caps and too bright sound of silver mica caps. Ceramic is even more agressive for my ears than polystirol, but I am not shure that I heard the best one.