Microphonics in VF14 and U47

[gyraf]

..a small piezo in parallel with tone cap..?

 

[Cqwet Dbdfte]

I knew Id seen this tube before somewhere and commented on it
View attachment 112285Its used in a Tek CF probe ,

Got one of those probes. Used with 1960's Tek 1S1 sampling plug in. Not very useful these days.

 

[paulcheeba]

I totally agree! I think that's why I love to build tube microphones.

I'm a big fan of the whole 5654/6AK5W/E95F family, they sound really good to my ears! (completely independent of the VF14, I have no way to compare).

I now have a proud NOS collection. Telefunken, RCA, GE, Phillips, Mullard...the nice thing is you get them for extremely little money. I pay between 3 to 6€ in original box per piece. Incredible, really a lot of tube for the money.

My favorite tube family so far for microphones. I have built up some circuits with it, the always sounds really good to me.The size, price, availability and the low microphonics and noise have convinced me, the whole package is right.

The Russian relatives I still have to check!

I agree, they are some of my favourite sounding tubes. They sound great in Horch and Soyuz. They also have pleased my ear the most in a 47 type way other than a VF14m which I do believe has a special depth. I have both the Grosser clones, the Fet and the glass tube and I have tried the Phaedrus plus I have 3 Neumann original’s, spare VF14’s and a bunch of Fleas, Heisermen, Voxorama and other 47 clones and nothing compares to the real VF14 in a good 47 apart from the little AK5W in a Horch etc. to my ear. I’m surprised it hasn’t been used more for 47 type mics. I tried an original Horch with an ac701k against my new ones and despite the difference in the $3k tube the original sounded no better other than maybe the Neumann capsule. In fact I liked the harmonics of the 5654 more.
I might put K49’s in my Horch mk 2’s and see how they sound…..
Has anyone built a DIY 47 with a 5654? What major changes would be needed to accommodate one in a 47 circuit?

 

[rock soderstrom]

Microphonics in tube microphones make me think about maybe designing in some positive feedback in a microphone circuit

..a small piezo in parallel with tone cap..?

...or you can use a tube that is notorious for microphonics. The EF42 (successor to the EF14) for Rimlock sockets would be a good choice. Maybe you can tune it by ear with some mechanical decoupling?

Does anyone have experience with the EF42 in U47 style microphones?

 

[rock soderstrom]

Has anyone built a DIY 47 with a 5654? What major changes would be needed to accommodate one in a 47 circuit?

I have done some promising experiments on this topic. In my opinion, the output transformer should be adapted in the direction of 10:1, the VF14 has more driver capabilities. Some are known to use the 2 tube approach to compensate for this, I'm not a big fan of that. Otherwise you could use an EF800 U47 schematic as a starting point, maybe reduce the anode resistor a little, the grid resistor doesn't have to be 1G either. Let your ears decide.

 

[granger.frederic]

...or you can use a tube that is notorious for microphonics. The EF42 (successor to the EF14) for Rimlock sockets would be a good choice. Maybe you can tune it by ear with some mechanical decoupling?

Does anyone have experience with the EF42 in U47 style microphones?

Hi, i tested both ef42 and uf42... it sounds very good but these tubes are indeed highly microphonic and ring like hell...
If you can deal with (modification on the tube dampening) , they work well in a 47...

 

[Tim Campbell]

I have also built some microphones using the EF42. A brilliant sounding tube that no attempt at all was made to dampen it's microphonics. Probably the most microphonic tube I have ever tried for audio

 

[terry setter]

Try an EF184 in triode mode, 200V plate supply, 75K plate resistor, bias about 1.1V, heat at 5.7V. I use a Cinemag NiCo 6.5:1 transformer. Wonderful!

 

[rock soderstrom]

Hi, i tested both ef42 and uf42... it sounds very good but these tubes are indeed highly microphonic and ring like hell...

I have also built some microphones using the EF42. A brilliant sounding tube that no attempt at all was made to dampen it's microphonics. Probably the most microphonic tube I have ever tried for audio

The EF42 (and the UF42) seems to have earned its reputation for microphonics ...ideal for experiments on this subject.

 

[rock soderstrom]

Try an EF184 in triode mode, 200V plate supply, 75K plate resistor, bias about 1.1V, heat at 5.7V. I use a Cinemag NiCo 6.5:1 transformer. Wonderful!

Thanks for the recipe. Yes, the EF184/6EJ7 is also very interesting in the U47 context. It is a frame grid pentode and the last development stage in the EF14-EF42-EF80X-EF184 series.

Due to its construction, it should have fewer problems with microphonics, right?

Edit: Very interesting in terms of price, great availability!

 

[terry setter]

I've been told that the EF184/6EJ7 was developed specifically to replace/update the EF86. I find that they work very well in that capacity. I don't mean pin-for-pin, I mean sound and potential applications. Sadly, they were the very last step in the progression of tubes before transistors took over, so not nearly of them were produced. They're a bit harder to find then I'd like. I have on marked "Zenith" in a U47 clone that is spectacular.

 

[rock soderstrom]

I've been told that the EF184/6EJ7 was developed specifically to replace/update the EF86. I find that they work very well in that capacity. I don't mean pin-for-pin, I mean sound and potential applications.

I don't think so, the tubes are too different for that. EF184 is clearly in the tradition of its predecessors and has been greatly improved. As I said, it is a frame grid tube that can do almost everything "better" than the EF86. Much higher anode current, slope, power, gain, that's already in the direction of a "super pentode" such as D3a, E280F or E180F, which might also do well in a microphone. Has anyone tried this? These super-steep pentodes are not so easy to handle.

They're a bit harder to find then I'd like.

That's not the case on my side of the pond, on the contrary, which I see as a big plus.

I'm going to try the EF184, if I've seen correctly it's the same pinout as the EF800.

 

[Tubetec]

The kinds of distortions that arise from microphony have little or nothing to do with the original musical content of the source and more to do with resonance and SPL , why people choose to chase that dragons tail I dont know ,

Allow the following pre-amp stage to do the talking ,as far as distortions are concerned ,and allow extra headroom and soft clipping to prevent distortion from becoming objectionable .

A point in time may come when humans are no longer required to do sound , an AI will take over and put people on the scrap heap , but it wont ever be able to anticipate whats coming down the line like a human opperator .
For me its the human interactive element that makes music ,not some dude with his head stuck in a computer in the studio ,to the detriment of all else around .

 

[Cqwet Dbdfte]

A high gm frame grid pentode (triode connected) with 120V on the plate, from a 240V power supply running 10 - 15 mA constant current would likely never clip from a mike capsule?
Unless you want a soft clipping device run it resistor loaded.
The 7788 has the highest (spec) gm I've seen.
The mike would run a little warmer than usual.
Any tube is microphonic, to some degree or another, frame grid tubes too. Pencil triodes may be an exception.

 

[Tubetec]

Neumann Thermo bottle ran with 10ma and 10k anode load , I bet thermal air currents are audible as they waft past the capsule , a tube mic that runs above ambient is a good thing , but hot air currents passing up and over the capsule ,no ,definately not what you'd want .

Frame grid tubes arent that immune from microphonics from my experience , C3G is one example Ive used , but never in a tube mic ,

 

[Tubetec]

Ever hear of the 6C45Pi ?

 

[Cqwet Dbdfte]

Yes, 45mA/V, mu=50 triode, strong heater. A bit overpriced. The U47 would benefit from running suspended with the cable end up, like the original Western Electric 47. Grid current and loading is an issue for condenser mikes. Not sure if that 6C45P would work well. The Neumann 47 ran ~50V plate, not that much gain, low B+. Not sure how much voltage swing was expected form it.

 

[Tubetec]

I havent tried the 6c45pi , but by all accounts grid resistance needs to be strictly limited to a low value under normal usage or it starts to oscillate ,
Still an aweful lot of power to dissipate in a tube mic body with very little air flow ,maybe low anode volts and underpowered heater as a self biased CF you could get near the kind of grid resistance required for tube mic ,
like all Russian tubes now ,hard to get and pricey

 

[terry setter]

I don't think so, the tubes are too different for that. EF184 is clearly in the tradition of its predecessors and has been greatly improved. As I said, it is a frame grid tube that can do almost everything "better" than the EF86. Much higher anode current, slope, power, gain, that's already in the direction of a "super pentode" such as D3a, E280F or E180F, which might also do well in a microphone. Has anyone tried this? These super-steep pentodes are not so easy to handle.

That's not the case on my side of the pond, on the contrary, which I see as a big plus.

I'm going to try the EF184, if I've seen correctly it's the same pinout as the EF800.

Rock Solerstrom, sorry for my lack of clarity, I meant that the ER184 was "the next generation" up from the EF86, thus the improvement in its capabilities to do similar tasks. And, you're lucky to have all those EF184s available. In the U.S., they mostly show up in 1s and 2s. A friend bought 250 "EF184s" and they turned out to be counterfeit. At least I thought that they were counterfeit, because the voltage readings (resulting plate voltage/bias current in the same circuit) were off by more than 50% from tubes I knew to be authentic, and there were no printed or etched markings on the tubes.

My distortion measurements using (real) EF184/6EJ7s in microphone circuits showed me that they liked being biased above 1.5 mA. If you use my recipe, your mic will be running close to 2 mA. Not heavy lifting for an EF184, and not a cooling issue in a U47-style body.

 

[rock soderstrom]

If you use my recipe

How big is your grid resistor? The original 60M or more?