IOaudio Inventor of the parrallel 408a tube configuration in U47 Clone ?

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I think that we dont have same numbers because I was talking about dynamic input capacitance. Dynamic input capacitance  indicates the tubes actual input capacitance under operating conditions. It describes not the physical capacity measured from control grid to cathode, but the actual input capacitance under operating conditions when  cloud of electrons is positioned between grid and cathode.
 
Find another example of a 47 implementing this tube design "before" Max's came to be and maybe you'll have a point but without that the thread is pointless.  If you're trying to say that because knowledgeable people mentioned "similar" configurations before the mk47 came out, in an attempt to vilify the micandmod mk47 variant that was used without Max's permission or blessing, then I'll say you're both too late, and without a case.

Max's was the first 47 to use parallel 408a tubes, and if you ask anyone that has one you'll find that it is one of the most elegant solutions to replacing the vf14 to date.  Some may prefer the ef14, some may like the ef86 and some may like other solutions.  IMO the twin 408a design is the best approximation yet and we have Max to thank for that.
 
if the measurement was wrong and the capacitance doesn't equate to greater noise with the 2 tube system, then I am missing the point ?

it is self evident that the 2 tube system is not the original

personally, I am more interested in what is the sound quality of the mk-u47 with the two tube system weighed against the cost of its build in relationship to what do i get for the same amount of money.

I am very happy to have purchased one as I certainly cannot afford a real 47,

I don't feel that max's build is a compromise in any way as it is obtainable and affordable; thx again Max !
 
Can anyone confirm Oliver's statement that the Saturn Sound replacement is 2 x 408a or 408b in parallel?

They have a list of high profile satisfied customers so it looks like a good solution.

Oliver's caveat about selection is also important and gives credence to the price charged by Saturn Sound.

The aim of the exercise is an affordable, available, consistent, reliable VF14 replacement with equal or better performance (eg noise) with the characteristic sound when used in U47

For those who want "hand carved by 1940s German virgins from WW2 Unobtainium", I think it is perfectly reasonable to stick such a label on any old tube and charge them $zillion.  They won't know the difference ..  ;D
 
Ricardo,

no, Oliver was talking about paralling the 407a, which is entirely different tube with two triode systems in one tube.
He claimed that Saturn sound was using 1. the dual triode 407a with its systems in parallel and/or 2. a single 408a pentode (connected as triode) like also telefunken USA does.
In my opinion the single 408a isn't able to drive the Bv.08 properly so i paralled them to lower the impedance.
Taking both heaters in series allowed me to use the tube(s) interchangeable with the VF14
vf14_vf14r.jpg


Moby,

if YOU are taking about Cdyn you should say so. But i doubt you looked up the term before throwing it out there, here is the first link after googling it: http://www.valvewizard.co.uk/gridstopper.html

"The dynamic input capacitance (Cdyn)  is:
Cdyn = Cgk + (Cga * A)
(Where: A = the voltage gain of the stage)

Using a typical ECC83 triode with a bypassed cathode as an example:
Cgk=1.6pF
Cga=1.6pF
A=60

Cdyn = 1.6 + (1.6 * 60)
= 97.6pF"

As long as we are talking numbers there is no need to bring this on a personal level, everything can be looked up, measured and compared in civil manners. 
Talking about the SOUND of the different solutions of course is a whole nother story and everyone's entitled to have his own opinion. OF COURSE!
In technical terms i think the numbers in this thread show that my solution works good on paper -  and the feedback i receive from people who actually use the MK-U47 confirm that.

So maybe this thread, although it's intentions from Flavio (or Gino?) are at least questionable, wasn't for nothing  8)

-Max



 
Hey Max, of course i was talking about Cdyn. If you read cerfully I told you that my numbers are from U47 circuit, so that is of course Cdyn,  an since the tube is in "special" heat and bias position numbers are quite different from static  numbers. But again, it really doesn't matter if it satisfy  the end user.  I would really like to stop talking about this subject because it can last forever. Last time when we start to exchange "numbers and measurings" you erased all  of your answers and  asked me to stop talk under your topic.  Again, I reacted becuse "invention" is too silly word for using tubes in parallel mode.  Do we agree here?
 
So you're saying that the numbers you have given:
"Vf14:
Grid to plate: 2.6pF
Grid to cathode: 6.7pF
Plate to cathode: 12.5pF"

are Cdyn?
Can you explain how you measured/calculated these numbers? Did you read the link i have given you, explaining how the Cdyn can be calculated from static C and voltage gain A?

The reason why i don't agree with you on anything here is, that you are wrong my friend.
Please educate yourself in the basics of tube characteristics, static Capacitance, Miller Capacitance etc before you are trying to throw dirt my way.
If you think you're right, prove it.
If you want to stop talking, admit that you're wrong and stop talking already.


 
Dear ioaudio,

you're making your business here with your MK47 (it's ok for me), but please don't manage the facts to justify that your so-called "invention" is the best VF14 alternative .

For me, two 408A are not suited in a mic, because of the the big amount of doubled capacitances, and because of the doubled microphonic noises, period. (a thread was opened about the noises a few time ago ...)
When i tried your design, It worked, but for a professional use, i think that the silence was essential, and the capacitances were softening a bit too much the transients...

the ONLY usable (and quiet) paralelled tube mic in the market, is the Neumann M147 and M149 with the 6111.
BUT check the capacitances of this tube : much much lower than one 408A, and it's one of the quietest tube ...

i don't want to denigrate your work, i just share my feelings...
 
I use them all the time in professional use.  Not a problem at all.

The noise which I and a few others discussed was found to be due to the sand resistors.  They thermally break down and get noisy.  Once that was replaced with a different kind of resistor the noise that sounded like bad tubes went away.

The two 408a tubes are the best replacement I have heard for the vf14.  I haven't heard the fet replacement that someone else came up with.  But those are super expensive as well and almost as hard to get a hold of as a good vf14 tube.  So I am very happy with the dual 408a tubes.  I would love to hear the fet option as well however.

My 2 cents.
 
I am wondering if there is a language barrier here ?

I am not as knowledgeable as many here on the technical said, but I have done a fair bit of research before buying max's kit.

A lot of the  (I'll be diplomatic) debate (?) seems to pivot on the word "invention" and at least  the OP's claim that Max has stated that he invented this ?

From what I understand, prior to Max's version being available there actually wasn't another version using the two tubes exactly the way Max's design does and Max was apparently quite aware of the circuit challenges he would confront from using two tubes and has designed his circuit in such a way to minimize those .

It seems to me that what Max has done is developed  an "emulation" of the original 47 circuit in a "best" attempt to re-create the original sonic performance while using the different tube circuit.  Knowledgable people I know and respect, who are using Max's mike are very very pleased with its performance.

I have never read nor seen a quote where Max claims to have  "invented" something in the way in which it is stated in this thread .
It also seems to be the case that Max is completely on top of the numbers associated with both the original and his design ,so arguing that seems like splitting semantic spec hairs.

Do fair minded people really see the  these facts differently ?
 
Wait - these are pentode tubes, not triodes.  The grid to plate capacitance should be much lower due to the effect of the screen grid...in fact, a 408a datasheet I found lists 0.02pF grid to plate capacitance (if the screen grid is at AC ground wrt. the cathode just like in Max's design).  It's why these are effective RF amplifiers (where a grounded cathode triode starts to look like a dead short at RF frequencies).

Even with a modest gain of 30, this would be adding less than 1pF to the overall dynamic input capacitance:  making Max's parallel implementation even closer to the original VF14 spec wise.

Even at these high output impedances of 100MEG+, the LPF formed between the output of the capsule and the input capacitance of a pentode would make a LPF at many 100's of kHz...I don't see "softening of the highs" being that much of a problem.

But in any case - what is being debated here?  :eek:
 
I'll start by saying Max I really love an appreciate your fine work and I have you 67 47 transformers in my builds an will most likely be buying  more!!; I've been eyballing  the 67 build ;)BTW so I mean you no offence by this post but I think what the original poster is  trying to say ?? is that regardless of the tube used the paralleled tube invention/ idea as a Vf14 replacement has been done before  by Saturn sound as pointed out by Oliver Archut. The difficulty with a Vf 14 replacement seems to be mostly with it uniquely low plate resistance characteristic at its operating point which very few other tubes exhibit. I recently found this out through discussions I had with resident genius Marik, who suggested winding a more appropriate transformer to suit more commonly found plate Z in order to support more tubes!!  I'll be testing this soon...Although in the meantime I've been using two ef802 in parallel  with your transformer which is sounding huge!.... It seems a single EF80 802 800 along with many other tubes is not a good pair for a 6.5 :1 Transformer when run at those operating points.
 
Dear Matador,

i can't understand your explanation about the capacitance, could you develop ? i'm curious ...

however, the input inter-electrode impedance (or insulation) forms mainly ( with a capsule) a High Pass Filter not a Low Pass Filter

when you put two tubes in paralels the input impedance is also reduced by 2, thus the low end suffers at around 50Mohms for 2 408A.

this misunderstanding explains why you didn't insulate the high impedance parts on your kits ...

i still find that the TRANSIENTS (not highs) are softened with two 408A
 
I am not nearly qualified enough to take part in the technical discussion.

And I won't go into possible motives of the OP and further contributors.

What I will say is that a (subtle) softening of transients isn't a bad thing per se.
IMOAE it is, or can be, one of the the pros of tube and tranny mics over TLM designs.

You can shoot me now.
 
granger.frederic said:
Dear Matador,

i can't understand your explanation about the capacitance, could you develop ? i'm curious ...

however, the input inter-electrode impedance (or insulation) forms mainly ( with a capsule) a High Pass Filter not a Low Pass Filter
Click to expand...

This isn't a description of the entire system:  yes, the capsule capacitance into the input impedance of the tube (which includes the grid resistance) forms a LPF...

But I wasn't talking about that:  the input capacitance of the tube looks to the capsule like a capacitance to AC ground (since typically the cathode looks like AC ground wrt. the grid), so the system shows a bandpass response, which is a HPF and a LPF.  The Miller effect swings into full force at very high frequencies, where the input capacitance wrt. AC ground starts to dominate the response.  Even basic Spice simulations can show this.

this misunderstanding explains why you didn't insulate the high impedance parts on your kits ...
Click to expand...

Good grief:  believe it or not, there are other types of insulation other than air (and many are much better).  This isn't 1960 anymore.
 
Your PCB material is maybe good enough in the beginning but after several years of ambient moisture , nobody knows...

that's why Neumann still use TEFLON in their 2014 microphones, as many other professional manufacturers...
 
granger.frederic said:
Your PCB material is maybe good enough in the beginning but after several years of ambient moisture , nobody knows...

that's why Neumann still use TEFLON in their 2014 microphones, as many other professional manufacturers...
Click to expand...

sigh, gee when I want to read, implied insults and speculations, I read GS, do we really need them here ?
 

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