Sujet Micro U47

Et là, pour ce type de micro qui chauffe beaucoup, il faut le monter tête en bas !!!

y a t il quelqu'un qui a comandé chez AMI ces dernier temps car j'arrive pas à les avoir par email

Citation :

Et là, pour ce type de micro qui chauffe beaucoup, il faut le monter tête en bas !!!

c'est une blague...??

What about tube substitutions for the VF14 valve?

The key to that question is: you have to understand the working principle of tubes. A tube with low noise, low microphonic values can give great results with the right amplification, once you find the right bias, the correct „Arbeitspunkt“ (operating point). So once you understand under which condition K2 distortion kicks in, and at which point K3 distortion, you get an idea of the overall level amplification profile of that tube. Under these circumstances i could make any good tube work, for example EF 86. Once it is tweaked to the right level and the right bias point for distortion, the behaviour of one good tube should not be so different from another good tube under the same condition.

Take guitar amplifiers for example, guitarists usually swap tubes and think „it is a telefunken and that is why the tube sounds better than another valve brand.“ But in reality each specimen behaves more or less different, some tubes of the same brand have distortion kicking in 2db earlier, others some 2db later. So while the the tube has the same name its individual behaviour is different. Which means there is no point to prefer a certain brand like Telefunken, Mullard and so on just for its name. In reality regardless of the brand all tubes behave slightly different and need to be adjusted. What i also find sometimes is that some tubes are outside of the working range, so they simply can not be adjusted. But in general you can use any GOOD tube.

I did a lot of tests, in which i also used small glass tubes and under normal conditions you would not hear any huge difference.

So while it is correct to say that tubes produce a characteristic sound, it is not correct to say that for an specific brand of tube will produce a specific sound that would not be achievable with other types of tubes.

So you are saying if is the BIAS and other parameters are adjusted properly, one can use any tube as substitute?

Yes, as long as it is a good tube.

Let’s be more specific regarding the U47, how did you go about making a good substitute for the original tube ?

I was not merely interested in replicating the VF14. Of course it helps if you know how to manufacture a 100% identical copy. That’s a good start, but it is as important to be aware of the problems the original VF14 had and how to avoid those problems.

Not every old microphone is in best condition, obviously. There are problems with noise, with hum, the tube being too sensitive for distortion kicking in, the amount of K3 (third harmonic) distortion. You should know what sounds right and where the problems are coming from. And since you are building something from new parts and you are able to resolve those problems – eliminate hum, reduce K3 distortion – if I am able to do it technically, i HAVE to do it, for myself. So I was not interested to get a picture perfect copy including the mistakes. I wanted an improved copy – better than the original.

By the way, the VF 14 is far from being a perfect tube. Why ? The idea behind it was to produce a tube which would work with just 2 supply lines plus shielding. The EF 12 for example is more comfortable but needs a separate supply line for the heater. You have to understand under which conditions microphones had been developed in the years before: at the time of WW2 there was a need for a simple mic for reporters, which would work with a single voltage for the anode and heater. Back then the military used a „battery suitcase“ which supplied 100 V and with that the mic was working fine. After the war most of the electrical infrastructure had been destroyed in Germany and so totally new and incompatible electrical networks were build from the ground in the british, french, russian and american sector. All of a sudden you had to deal with 100 V DC, 110 V DC, 110 V AC and 220 V AC.

For that reason it became necessary to develop a mic which required only 100 V and still could be used anywhere. That was only possible with the VF14.

Citation :

Et là, pour ce type de micro qui chauffe beaucoup, il faut le monter tête en bas !!!

c'est une blague...??