Measured VF14 characteristic

[Moby]

Dear Moby,

i'm very curious about your mod also, and it's on the way.I've received a bunch of 13CW4 NIB NOS.They seems to be in perfect shape.
I need to mod the Psu as well, to revert the mic into a conventional U47 schematic.
As the mic now needs around 55mA, i need to calculate the RC rail in the PSU as well.I don't want to regulate it.
I'm in holidays for a week ,i think i'll do that when i'll be back.
I can't wait too, but i assure you that i'll report back here with a very detailed post asap.
Thanks again for the trick

Kindest regards
Fred

PS: is there anyone here who is familiar with Germanium transistors into microphones ?

U welcome. Its good to have a bunch of 13cw4 because their only weak side can be microfonics. It's not so often like with  big steel tubes but my experince is approx. 2 of ten are unusable. Of course, that's just mine experience from 50 pieces

 

[granger.frederic]

Thanks Moby,
Yes, my initially mounted 13CW4 was microphonic.

For people who read this topic and don't understand my answers to Misha,

i must tell that he has deleted nearly all his posts...

Not very fair play ...

Cheers

 

[o3misha]

Fred, I keep all info, which is "in-topic". In all my deleted posts I answered on your provoke, trolling messages.  Your last post just confirms my words. I'm sure, that I did all right,- it was not un-fair.  Do you prefer to continue acrimony and not meaningful dialog? You prefer to quote outdated  clichés that have long been not relevant,- I prefer to test all new ideas my self. You're too sure of the correctness, so do not want to listen to others. I don't think that it was right decision to share my esperience with you, as you don't need it. You may enjoy the win, pal. 

 

[granger.frederic]

What a strange attitude !

you posted some very useful posts, others more than controversial.
I didn't want to be provocative.Sorry that you missed the point.

BUT you'd better ASSUME your writings like everyone in this forum, including me, and that's why i don't want to delete or edit my posts.

everyone who can read them, can make his own opinion about what i'm saying in this topic.

it's a shame that it's not possible about you anymore.

this LAST post is maybe useless, but i'd like to make thing CLEARER.

 

[o3misha]

Understand why your posts have touched me: I have shared my experiences, which was closely associated with the  people I very respected: Andreas Grosser and Siegfried Thiersch. I shared the facts that contrary to popular opinion. In particular: the dangerous polarization voltage for the capsule, how to deal with the advent of high-impedance circuits leaks, why it is necessary to work with the modes in microphone for each lamp, before to refuse it. And you all my posts interpreted through the prism of common stereotypes. It turned out that I give false information and the authority to denigrate others. I could not convince you that I have not said a single word of a lie or untested info. But if you do uncredited, means-can not believe others. The most annoying thing that you do not have any evidence that I gave wrong or incorrect data. But I'm convinced - I deleted everything about our correspondence with you. In the future, I'll be careful. I hope to start the new topic about EF14, but I need time.

 

[granger.frederic]

I'm back to report my feelings with the 13CW4 nuvistor in a U47

i have a 110V B+, 11V heater, cathode fixed at 0,65v with 11,5ohms .

i've selected 1 of 10 non microphonic and that's imho the biggest issue with this tube.

it sounds quite good and well balanced with non sibilant highs but sometime sterile and clinical on some tubes.

i've found only one of 20 completely usable !!!!

the best 13CW4 installed in my u47 (with an KK47), is very quiet and dynamic, and has a lot of gain,
the low end is here, the transients are faster than EF14 AND EF12.

i didn't notice any sonic difference with 0,65V bias and a conventional 1,1V , my ears were maybe tired but even after several listenings , it's not that evident.

However, after several shootouts , i prefer the "robustness" of the EF14 sound, but it's just my 2 cents.
The sound cut through the mix more easily , and the low mids are more U47 and the transients are softer, and that's fine with my voice and my strat/deluxe reverb 

thanks again at Moby ...
Cheers
Fred

 

[Moby]

Dear Fred I'm glad U succeed. Well, I was comparing the 13cw4 to Vf14m and it "sounded". By measuring K2 & K3 it was damned close. But again, sonic can be the matter of taste.  8)

Edit: Fred, which brand 13cw4 did U use?

 

[granger.frederic]

I've two different brands: RCA and Sylvania.
The best one in my bunch is a Sylvania.
My RCAs samples are too microphonic or noisy 
Is there a difference between the brands for you ?
I can't compare K2 and K3 as i don't have a good working VF14 and probably never will.
I wonder also if, a hotter bias like 0,6v, could pump the tube more quickly...?

yes the nuvistor sounds good, but i think the steel tubes like vf/ef/uf 14 are microphonic and "pick up" the mids/low mids, inside the mic body, more than a nuvistor. After all, that's a part of the U47 sound...
cheers

 

[Moby]

I've two different brands: RCA and Sylvania.
The best one in my bunch is a Sylvania.
My RCAs samples are too microphonic or noisy 
Is there a difference between the brands for you ?
I can't compare K2 and K3 as i don't have a good working VF14 and probably never will.
I wonder also if, a hotter bias like 0,6v, could pump the tube more quickly...?

yes the nuvistor sounds good, but i think the steel tubes like vf/ef/uf 14 are microphonic and "pick up" the mids/low mids, inside the mic body, more than a nuvistor. After all, that's a part of the U47 sound...
cheers

Yes, Sylvania sounds Ok, I tried just couple of RCA's and they were same like yours :/ Unfortunatelly, yes, hotter bias will pump the tube faster, but not sure how fast. At least, those little *******s are available so we can buy the bunch of them for a price of Vf even of  Ef , UF
Your theory about bigger steel tubes may be correct but  only with non selected tubes. Selected steel tubes has low noise and they are less microphonic. Top Vf14m should be quiet and immune to outside noises.

 

[granger.frederic]

OK your probably right, but if you or someone with a good VF14M could do a little test....
simply put a 80pf cap instead of the capsule and plug the mic.
then speak or sing near it, and listen if a sound is leaking...you will perhaps be surprised.
thanks.

i think i'll revert it to ef14, with my tweak: h=6V , suppressor grounded ,B+= 105V, Self bias with 2,7k and 47uf
i have a very warm and soft sound very close to the nuvistor and a EF12 which HAVE the suppressor plugged to the cathode inside the tube, and i think that's the key...

The big issue with 13CW4 for me is the big amount of heat inside the mic, produced by the 1,8k dropping resistor, and in the PSU also.i must say that the U47 body acts like a heatsink but that's really not enough .
With that amount of heat and the hotter bias, i think that the reliability will not be good.

the EF14 with 6v and a separate H+ is hot but not in that range at all.
Cheers

 

[o3misha]

You may put 1.8 kOhm resistor in Psu without problem, but 70-75 degrees its not big problem for U47 inside parts. Ef14 and Ef12 have different inside construction, so it is not enough to put g3 on ground. BTW, you may avoid using bypass cathode cap. Use the transformer to block DC like it was made in UM57. It is interesting way....

 

[granger.frederic]

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...

using the OT on the cathode should introduce a little feedback in the circuit, but it's an interesting way to experiment.

EF14 is different than an EF12 for sure.
EF14 is more a VF14 than a EF12.
But the EF14 sounds different in a U47,even if it measures the same, using the same parameters, including a proportional under-heating at 4,75-4,95V
The highs are more aggressive.
By using a such under-heating, the EF14, which has a different heating construction/filament, cannot emit enough .
If you use 5,8-6V, the emission is at specs, but the sound is still muddy.We don't want that in a U47, even if the highs become more accurate.That's why i put the suppressor to ground.The suppressor in a pentode is here to solve the issue of secondary emission ,then the tube can have a higher current output, a wider headroom, and the sound becomes clearer with still a little under-heating.
Self bias vs fixed bias is then a matter of sound and taste, and with an EF14 i prefer self bias.This compromise is the best i can have with this tube, and i like the sound better than a EF12 which is more flattering, thin, HIFI,and doesn't cut through a mix.

But, i must admit that the nuvistor is a very interesting animal, as it has the deepness and authority in the mids that i like.The highs are softer and the low end is tighter.It's somewhat a mix between a VF14 and a AC701.

I prefer it, in the overall performance, than the EF14.

My only fear is the amount of heat but time will tell ...
(Putting the 1,8k in the PSU will introduce some noise ,through the cable, in the cathode)

Cheers

 

[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...

U welcome again. Honestly I have never measured the inside temp but electronics parts are not humans so I don't care too much about it If you like to extend the Nu life u can add the aluminum cooler on t
The only sensitive part is capsule but it's positioned opposite from R4 and also separated with metal barrier.
Yes, 75c is too much for inside air, but some parts can be hot like that in the core. Since the R4 (1780R) is coupled to aluminum body it can't be and it shouldn't  be so hot. If you can hold the body for some time it's not more than 45c BTW, Anything above 48 degrees C is scalding and can damage human tissue . Not too scientific but it works

 

[granger.frederic]

sorry Moby i thought you've answered me but it was Misha...

yes i can hold the mic so you're probably right, the temp should be around 50/60°c inside, thus the components should resist.

PS:About the UM57, the way the cathode is biased needs a special output transformer.

Cheers
Fred

 

[bruno2000]

Greetings,
Any of you gents tried the 7586 Nuvistor?  It is used in the Neumann u64 mic.
I was thinking about using it in a C12 clone.
Thanks in advance for the comments.
Best,
Bruno2000

 

[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.

 

[o3misha]

PS:About the UM57, the way the cathode is biased needs a special output transformer.

Cheers
Fred

BV08 is ok for this.

 

[granger.frederic]

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

Bruno, i've tried the 7598 as i actually use one in a AR51 telefunken(which sounded awfull). it sounds much more like an AC701.very quiet also.it has a very low output impedance and thus you will perhaps have to slow down the transients a bit, with a 100/220pf on the anode to ground.(it depends of your capsule).Even with that, the mic with a 7598, should sound more like C12/ELAM 251, than a U47.I like to use a quite big output transformer with this tube, like a T49 ami or another lower ratio OT, and had bad feelings with T14 and a cm-2480 (too bright), but it really depends on your capsule frequency response.
If you want to deal with a pure triode mode in your U47, go with the 13CW4 or 6SJ7/12SJ7 for example...

Dylan, the higher temp should be a part of the U47 sound, by a decrease of the air humidity, around the capsule.

cheers
Fred

 

[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.

 

[bruno2000]

Bruno, i've tried the 7598 as i actually use one in a AR51 telefunken(which sounded awfull). it sounds much more like an AC701.very quiet also.it has a very low output impedance and thus you will perhaps have to slow down the transients a bit, with a 100/220pf on the anode to ground.(it depends of your capsule).Even with that, the mic with a 7598, should sound more like C12/ELAM 251, than a U47.I like to use a quite big output transformer with this tube, like a T49 ami or another lower ratio OT, and had bad feelings with T14 and a cm-2480 (too bright), but it really depends on your capsule frequency response.
If you want to deal with a pure triode mode in your U47, go with the 13CW4 or 6SJ7/12SJ7 for example...

cheers
Fred

Thanks for the observations and suggestions.  I have several original u64s that use that tube, and am quite happy with their sound.  The C12 sound is what I am going for in my current builds.
Best,
Bruno2000