Difference in sound between a AC701k and 6072A in a ELA M251?

[rock soderstrom]

Yes, the 408a pentode (a 20V version of the 5654/6AK5W/E95F family) is a good sounding tube, I like the whole family
Advantage of the 407a double triode is the 40V heater and the lower Ri. In this respect the 407a is quite similar to the E88CC (and somehow to the VF14 wired as triode)

 

[Barry Hufker]

"Many years ago I put a real VF-14 up for sale on Ebay and Telefunken Electroakousic bought it within minutes. Somebody got a mic from them with a real one in it!"

I don't know if it happens anymore, but I've known of Telefunken putting a real VF14 (non-K, but still measured the same) into their U47...

 

[Accelerator]

@terry setter​

Does anybody know what tube Telefunken Electroakoustic put inside its VF-14K?

It’s a LM Ericsson 6028 - 408 A tube or any other Sylvania 6028 - 408 A tube that they can have in their hands for just “a dime a dozen”, then they put it with a resistor in a metal can and then they sell it to everybody with their 11.790 € Telefunken U-47 microphone…

After that you have paid all of this ridiculous & hilarious overprice for their 11.790 € Telefunken U-47 microphone and after that you had expelled their warranty time and if you feel that their VF14K Vacuum Tube (U47, U48) tube it’s a little bit too “noiiiiiisyyyy” for your likes, so it is the time for you to replace it with a new one, they are fully joyful to support you for your new replacement by selling you a new one, for only just $750.00 U.S.D.

Yes, that’s right…

What a lucky we are all that we all have this “God Bless America” “Telefunken Electroakoustic USA” Company with their proudly "Made in USA" VF14K Vacuum Tube (U47, U48) for only just $750.00 U.S.D.

Many years ago I put a real VF-14 up for sale on Ebay and Telefunken Electroakousic bought it within minutes.

Very logical as they needed a real Telefuken AG GmbH VF-14 M tube for their “Telefunken Electroakoustic USA” U-47 “Demo” microphone, for the “Demonstration" video comparisons at Vintage King videos…
But as I believe this Telefunken U-47 microphone with the real Telefuken AG GmbH VF-14 M tube remains guarded locked in their safe closet...

 

[ricardo]

anyone got views about 'triode connection' with G2 & G3 together ... vs the more usual method with G3 connected to cathode?

What is the measured difference? Noise? THD?

Sound?

 

[Accelerator]

@ricardo​

anyone got views about 'triode connection' with G2 & G3 together ... vs the more usual method with G3 connected to cathode?

What is the measured difference? Noise? THD?

Sound?

Direct from the lion’s mouth…

TEST Microtech Gefell M92.1S & Yamaha YC series


Ellen Harper and the Mama's Boys - from OK to LA


ACOUSTIC BASS RECORDING WITH M 990 – LMP Studios Claremont

 

[Latie]

anyone got views about the MG method for 'triode connection' with G2 & G3 together ... vs the more usual method used by Neumann with G3 connected to cathode.

see Accelerator's
https://groupdiy.com/threads/differ...1k-and-6072a-in-a-ela-m251.88876/post-1172311

IIRC, EF86 triode connected, usual method, has characteristics very similar to ECC83 or maybe 82

Take it with 2 grains of salt:
I don't have a tube mic, but I did have a tube preamp (a weird adaptation of a guitar circuit to take advantage of a transformer input that fell into my hands). I tried the only low output impedance valve I had at hand, a 5965. It sounded nice; true that it didn't have a transformer output, it went directly to the audio card (unbal in). Strange, I know; I used it many times, mostly recording voice. Later when the valve broke I tried the 12ax7 that the circuit originally had, it wasn't the same (obviously?). I tried 12ay7, and 12av7 (supposedly the same): no good. Finally I got a 5965 and it's the one that works / Nowadays I don't record that often, and I use an MR18 that sounds good and time to time a Neve clone with Carnhill. You make me think of resurrecting that monster.
But to the question: if one day I build a tube mic with 12**7 family, I'm sure my first test would be a 5965.

Saludos!

 

[gyraf]

If you use anything but ac701 or vf14, you should be prepared to try out several tubes of same type. This because the parameters needed for condenser frontend are not specified anywhere else.

Of the 12xx7 types, the ecc83 is by far the worst for this purpose, 82 better, and '81 often usable

/Jakob E.

 

[k brown]

Yes, the 408a pentode (a 20V version of the 5654/6AK5W/E95F family) is a good sounding tube, I like the whole family
Advantage of the 407a double triode is the 40V heater and the lower Ri. In this respect the 407a is quite similar to the E88CC (and somehow to the VF14 wired as triode)

Dave Royer was a big fan of the 6AK5; used it some very compact mic pres that he built into surplus ammo cans; even a version that was battery powered! (I'll see if I can dig up the schems he sent me; unfortunately I didn't keep the original emails). I'd emailed him about subbing the 6AK5 in his 5840 mic circuits (he said it subs quite well, and I built a couple of mics with them).

The pres were one tube as a pentode fixed gain stage followed by a second tube, triode connected as a cathode follower.

 

[k brown]

Dave Royer was a big fan of the 6AK5; used it some very compact mic pres that he built into surplus ammo cans; even a version that was battery powered! (I'll see if I can dig up the schems he sent me; unfortunately I didn't keep the original emails). I'd emailed him about subbing the 6AK5 in his 5840 mic circuits (he said it subs quite well, and I built a couple of mics with them).

The pres were one tube as a pentode fixed gain stage followed by a second tube, triode connected as a cathode follower.

Shown with the AC and battery PSUs, and at lower right with an input level control (for unbalanced input).

He said he didn't usually build them with out trafos, as he never felt the need for balanced out at line level (this was almost 20 years ago; he might feel differently in today's RF-polluted world).

The circuit itself as shown has 43 dB gain (~36dB w/o the cathode bypass cap), plus the gain of whatever input trafo is used.

No phantom, as he used these with his own DIY tube mics.

In case it isn't legible, in the battery supply, the 12v battery is a lead-acid alarm battery. I forgot what he said the battery life was of the nine 9v batteries when powering two channels (and, yes I drew the battery symbols backwards!).

 

[rock soderstrom]

Dave Royer was a big fan of the 6AK5; used it some very compact mic pres that he built into surplus ammo cans

I think he is still a fan of this tube, but in his current tube microphones he mostly uses the 5840, which is the sub-miniature version of the 5654/6AK5w. Technically they are almost identical, but I prefer the 5654 because of the socket.

The circuit itself as shown has 43 dB gain (~36dB w/o the cathode bypass cap), plus the gain of whatever input trafo is used.

I know this circuit (from you) already, I like it, it shows some design ideas typical for David Royer. The PSU is similar the Royer LDC/SDC mods.

I have also built a mic pre amp with the 5654, a conversion of the GATES SA70 circuit, which works perfectly. I have realized this PCB project with two Telefunken 5654 and a tiny 1:20 IPT also from Telefunken/Haufe. Very nice for acoustic guitars and vocals, the 5654 type tubes have beautiful harmonic distortions.

 

[rock soderstrom]

408a with some resistors can be used as a drop in for VF14. I’ve done that in some original U47 with a bad VF14. It’s a good sounding tube but often noisy. I find that lowering the plate resistor makes it sound fuller.

A small addendum: the 5654 family tubes feel more comfortable with a 10:1 transformer than with the BV08, which only has a 6.5:1. I don't know if TELEFUNKEN USA takes this into account in their microphones. I would do it...

That's why I find the 407a/b tube interesting for this application, as it could probably cope better with the original BV08 transformer and has the 40V heater as well. At least theoretically, I haven't tried it yet.

If you use anything but ac701 or vf14, you should be prepared to try out several tubes of same type. This because the parameters needed for condenser frontend are not specified anywhere else.

Jakob is right, the question remains how the 407a/b for instance will cope with the high impedance situation...

 

[pasarski]

A small addendum: the 5654 family tubes feel more comfortable with a 10:1 transformer than with the BV08, which only has a 6.5:1. I don't know if TELEFUNKEN USA takes this into account in their microphones. I would do it...

That's why I find the 407a/b tube interesting for this application, as it could probably cope better with the original BV08 transformer and has the 40V heater as well. At least theoretically, I haven't tried it yet.

Jakob is right, the question remains how the 407a/b for instance will cope with the high impedance situation...

I just started building a C12/251-esque mic with a 5670 tube. I've built one before. After experimenting with the plate curves, I've concluded it needs at least a 9:1 transformer for a typical microphone operating point. Of course, I don't know how the curves will really look with a high value grid leak resistor.

David Bock used the 5670 at some point with his 251.

 

[rock soderstrom]

I just started building a C12/251-esque mic with a 5670 tube. I've built one before. After experimenting with the plate curves, I've concluded it needs at least a 9:1 transformer for a typical microphone operating point. Of course, I don't know how the curves will really look with a high value grid leak resistor.

Thanks, interesting!

David Bock used the 5670 at some point with his 251.

I also saw that during my recherche, I think he was or is the only one who has ever used this type of tube in microphones.

 

[tomas.borgstrom]

That's why I find the 407a/b tube interesting for this application, as it could probably cope better with the original BV08 transformer and has the 40V heater as well. At least theoretically, I haven't tried it yet.

If my memory serves me well someone wrote on this forum that he really tried to get the 407 to work in a U47 circuit but gave up due to noise and distorsion.

 

[Accelerator]

@tomas.borgstrom​

If my memory serves me well someone wrote on this forum that he really tried to get the 407 to work in a U47 circuit but gave up due to noise and distorsion.

Oliver Archut (RIP) said it very clear and straight in his post back in time, at February 13, 2009…

All the other things about the “recreation” of the “VF-14(k)” tube by the -all American- “Telefunken Electroakoustic USA” are just liberal capitalistic marketing…

Even for a fair and honest discussion of the subject, it should be disclosed that Oliver Archut was a supplier to Telefunken-USA.

Telefunken/USA's "VF14k" tube = WE 407/408A?

 

[rock soderstrom]

If my memory serves me well someone wrote on this forum that he really tried to get the 407 to work in a U47 circuit but gave up due to noise and distorsion.

I used the search engine last night to search all posts on groupdiy for 407a mics info. Most of them refer to a rather negative statement by Oliver Archut, the only one who has had real positive experiences is member @shabtek. Maybe he can contribute something to this topic? He uses the 407a together with a Dale M7 in a DIY U47 style build and seems to be very happy with it.

 

[Buttercup1]

Would be fab to know some more details of which dropper resistors etc that have successfully been used to make a 407 or 408 work in a stock U47 circuit..... I have a couple floating around....

 

[tomas.borgstrom]

Would be fab to know some more details of which dropper resistors etc that have successfully been used to make a 407 or 408 work in a stock U47 circuit..... I have a couple floating around....

Unfortunately it differs between the brands

If you're building a clone use a separate heater supply and find the tube and circuit that you like the most.

 

[rock soderstrom]

Unfortunately it differs between the brands

Really? Can you explain that in more detail?

 

[tomas.borgstrom]

Really? Can you explain that in more detail?

It was a while ago since I experimented with it. I tried a lot of tubes but got tired of it. It quickly gets quite expensive since there are so many rejects due to noise. Western electric sound good and have ok noise levels (but the best are still often more noisy than accepted if you were to sell a microphone). LM Ericsson were almost all to noisy but I remember finding one with the best noise levels. I tried other brands as well but can't remember in detail.

You have to use a resistor before the heater to get 20V. I think in some I didn't need any at all. You can also add a resistor to increase the cathode resistance if needed. Start with inserting trimpots in both places and adjust to taste.

Once again, if you don't have an original U47 that you don't want to modify. Aim for another circuit. The wired dropping resistor gets even hotter and the match with the BV08 is not optimal.