American octal steel tubes in LDC microphones?

[terry setter]

But utterly different technology. Electrostatic electron beam deflection vs. electrodynamic contraption.

Yes. Similar function, different technology. When I see the picture of the "Betriebsstandanzeiger", it instantly transports me back to the magic eye days.

 

[terry setter]

Which is?
Sorry, I don't catch it... I'm not versed in cryptic messages.

Sorry, I didn't intend to be cryptic. I was thinking that the comment I had referred to ("A popular workaround for the reduced low end of the U47N nuvistor substitution is to replace the output transformer with BV11 type) framed my response as supporting the idea that a BV11 mates nicely with a 13CW4 and would likely be closer to the sound of a VF14/BV08, especially in reproducing low frequency content. That is to say, when a person makes the decision to replace a VF14 with a 13CW4, they do not get optimal performance (at least as per my experiments). It's necessary to change the operating points of the tube - not in the same way that was suggested by Neumann at the time - and then they will still have to deal with the handshake between the 13CW4 and the BV08. The BV11, with its higher turns ratio, again, as per my experiments, will be a better overall approach to retaining as much of the original character of the microphone as possible.

I realize that my ears and musical taste might be more sensitive to particular sonic shifts that occur when changing tube, operating points, and transformer than someone else's ears and taste. By this I mean that I might want to retain some quality in the low end more and be less concerned with the top octave, whereas someone else might be just the opposite. This fact has been part of the complication of trying to fly a U47 without a VF14 since those tubes became very hard to get. There doesn't seem to be any single approach to retro-fitting a U47 that a majority of people agree maintains the greatest degree of similarity between how the mic used to sound and how it will sound when the circuit is significantly changed. So, everyone picks their approach, based on parts availability, costs, their preferences in sound, etc., and takes their best shot at coming out as well as they can. (Maybe we should also talk about how all of the original M7 capsules are coming apart after all these years and this is very significantly changing the sound of the mics).

Relative to the low frequency response of the stock U47 (as opposed to one with a 13CW4 nuvistor in it), my tests showed that in a stock U47 the resonant bump that is caused predominantly by the interaction of the output capacitor with the transformer occurs just at or very slightly above 20HZ. This is part of the reason that some folks have made statements like: "The U47 is different than other mics. If you put a smaller output capacitor in it, the bass actually increases." Well, in a sense, that's true, because a smaller output cap brings the resonant bump higher up into the the audible region, so it kinda does sound like it has more bass. However, if you look at frequencies below the new resonant bump, you'll see that they are in steep decline, because they're now below the passband of the output cap. Most people listening to most music would be likely to hear "more bass" from a bump at 30HZ than one at 20. This is why using a BV11 with a tube OTHER than a VF14 might sound more like what a stock U47 sounded like.

I happen to be working on a "new" mic build that uses a Cinemag BV11 clone and I'm getting to know the characteristics of that transformer, which so far, I'm pretty impressed with. My goal is not to build a U47 clone. I'm wanting to go in the direction of an M49, so my final landing will be somewhere different than where a BV08 would take me. But I'll attach some screen shots that might be of interest. I won't have an original Neumann BV08 in these shots, but I'll include an AMI T47, a Crimson 2766 (BV08 clone), a BV08 clone by Andreas Grosser, a Cinemag 2481 "NiCo" (a transformer that I like the sound of very much), and the Cinemag BV11 clone. In fact, I'll add some decent, but physically smaller 6.5:1 transformers to the image collection to partially address Abby Road D Enfer's response to my comment about the effect of small physical size of transformers (above). In am loathe to go into my '57 Telefunken long body and disconnect its 66 year old wiring to run test signals through the transformer, though I would really like to see exactly what it would look like. If anyone has such a thing, please let me know! Maybe someday I'll have the conviction and necessary resolve to go into my Neumann U48, which has a BV08 that was re-wound by Oliver Archut using the original (vintage) laminations. That would probably give me a pretty good sense of what's going on inside my U47's transformer.

These shots of my scope are a bit blurry due to the florescence of the screen. It's easier to see details when looking at the scope than when a camera creates these images. The transformers are being driven at 5.5VAC (because .25V off a capsule comes out of my Mu 22 test circuit as 5.5V). The 10KHz shots are all square waves and the low frequency shots are all sine waves, though you might not know that from looking at the significant distortion of some of the smaller transformers..
GAD, I SEE THAT THESE SHOTS DO NOT SHOW UP IN THE ORDER I UPLOADED THEM. SORRY, YOU'LL HAVE TO HUNT AND PECK A BIT. Note: for the AMI T-14 I didn't bother with 20HZ. It's response at 20HZ wasn't worth photographing. All but one of the smaller transformers were pretty well behaved by the time I got up to 30 cycles, but you'll see that I started at 40HZ with the "Chinese Junk". That's so you could see how far up in the spectrum it was failing (visible on my scope up to 60HZ).

 

[abbey road d enfer]

I still don't understand what are the consequences of replacing a BV8 with a BV11. I understand that the higher nominal impedance (and associated leakage inductance) may affect HF response; is that your criticism?

 

[terry setter]

I still don't understand what are the consequences of replacing a BV8 with a BV11. I understand that the higher nominal impedance (and associated leakage inductance) may affect HF response; is that your criticism?

Hi, I'm not at all critical of replacing the BV08 with a BV11 in circumstances where one is forced to use a different tube than the VF14. On the contrary, I'm in favor of it because, if it is done well, it is possible that you will end up with a mic that is truer to the original sound of your U47 than if you stayed with the BV08. Thus my comment a few pages ago that I hoped "folks would catch the significance" of George Toledo's suggestion that "A popular workaround for the reduced low end of the U47N nuvistor substitution is to replace the output transformer with BV11 type." The significance is positive, not negative.

 

[rock soderstrom]

Thanks Terry for your detailed experience and informative measurements.

The transformers are being driven at 5.5VAC (because .25V off a capsule comes out of my Mu 22 test circuit as 5.5V)

Two question regarding the Mu 22 test circuit. Which tube was used? In which circuitry?

Is not quite clear to me or did I read something over?

 

[entropy]

[..]
PS: How the hell does this "Betriebsstandanzeiger" (operating status indicator) in the heating circuit work?

That kind of devices where very common in after WWII telephone equipment, they are related to a "Drehspulinstrument" (rotating coil meter?). I've owned some of them when I was a kid, but I don't think that one is left in my stash...

The german name for them was "Schauzeichen". They consisted of 2 long tall coils wound on a U-shaped iron core and an steel wing on the top that could rotate 90 degrees with a spring to rotate it back.

I know a source of 3pcs. in Germany for 8€, I would take one of them.. If you are interested open an conversation with me, this is my 8. post here, can't start conversations myself.

Regards,
Holm

 

[rock soderstrom]

That kind of devices where very common in after WWII telephone equipment, they are related to a "Drehspulinstrument" (rotating coil meter?). I've owned some of them when I was a kid, but I don't think that one is left in my stash...

After the explanation of member abbey I had understood it so far, nevertheless many thanks!

The german name for them was "Schauzeichen". They consisted of 2 long tall coils wound on a U-shaped iron core and an steel wing on the top that could rotate 90 degrees with a spring to rotate it back

"Schauzeichen" - I like these old technical terms that no one knows anymore today! Good explanation of how it actually works. A moving coil meter with a reset spring.

I know a source of 3pcs. in Germany for 8€, I would take one of them.. If you are interested open an conversation with me, this is my 8. post here, can't start conversations myself.

I don't need one, but I can imagine that this could be interesting for other members here. Thanks Holm

 

[rmburrow]

I hope that folks catch the significance of this...!

Has anyone tried a 6J7 (1620), 6J5, or other grid capped octals in a "u47" and compared the results to original?

 

[terry setter]

... Two question regarding the Mu 22 test circuit. Which tube was used? In which circuitry?

I used a Simpson signal generator into the grid of a 5840. The 5840 is run at 190V B+ and the plate feeds a .68mF/450V Auricap. I swap in various transformers and load them with 1500 Ohms. I can also use this to test output caps, the effects of various heater voltages, etc. The scope is across the secondaries of the transformer (across the 1500 Ohm resistor). When I'm getting picky, I use FuzzMeasure software to get very specific read-outs and graphs which have helped me dial-in the particulars of my designs. My final clone circuit for the Neumann U47 was within 2dB across the first seven harmonic partials. I was able to get close using my ears and a scope, but to get it to the point where I could not tell the difference between my clone and my actual U47, I had to use the software. Otherwise, there were just too many variables.

 

[rock soderstrom]

Very informative, thanks a lot!

 

[abbey road d enfer]

I used a Simpson signal generator into the grid of a 5840.

Do you feed the signal via a capacitor representative of the capsule's capacitance?

to the point where I could not tell the difference between my clone and my actual U47,

Yours has a VF14 or a nuvistor?

 

[terry setter]

Do you feed the signal via a capacitor representative of the capsule's capacitance?

It depends on what I'm trying to measure. Where a capsule's characteristics would be influential, I use a capacitor. I'm currently using 36.6 pF and, someday, will experiment with a range of cap values in order to understand how I can best emulate the nature of various capsules. If I'm just trying to measure the Mu of a circuit, or something like that, I'll go direct to the grid from my signal generator's 600 Ohm terminal.

Yours has a VF14 or a nuvistor?

VF14M

 

[13engrsapper]

I can't say I see any clear trend of available 1620's being any better than 6J7's, after years of running a bunch of channels of that type. They also seem to last forever in conservative circuits, which mics usually are. I pulled 6J7's out of Gates SA-70's I'd run nearly 20 years then selected another best new set, took measurements, the old ones were barely down on current draw, no different on noise.

They are also not all that cheap any longer - better than some, but I think supplies are dwindling as we have been watching prices for good tubes climb for awhile now.

 

[rock soderstrom]

They are also not all that cheap any longer - better than some, but I think supplies are dwindling as we have been watching prices for good tubes climb for awhile now.

This is true for the 1620's but the 6j7's (steel version) are still super cheap here in Germany. You can buy them for 5-10€ each, top NOS quality from US premium manufacturers.

 

[13engrsapper]

This is true for the 1620's but the 6j7's (steel version) are still super cheap here in Germany. You can buy them for 5-10€ each, top NOS quality from US premium manufacturers.

OHHHH, well. We stopped going to Germany just before Covid. Honestly we had never looked for American tubes over there! I did look at the Soviet "equivalents"

OK - time to fire up the shipping chain. I have a friend with a large shipping warehouse in Wiesbaden, once a month he ships things back to the US; let's load up that pallet with all of our US tubes. lol

 

[emrr]

1620's seem to be getting harder to find from dealers, but prices aren't anywhere near keeping up with inflation. They were $10/ea back in the late '90's. Tons of stupid gouger prices on ebay/reverb, of course.

 

[13engrsapper]

1620's seem to be getting harder to find from dealers, but prices aren't anywhere near keeping up with inflation. Tons of stupid gouger prices on ebay/reverb, of course.

I think I just need to keep my head down, and continue quietly working with my metal clad tubes - made to withstand 1500G's while running ;-) I have bought up a ton of proper sockets for the over the years. I am having troubles finding some of what I need in those too - just in tube characteristics. Hoping to have prototypes to drag around to the studios by fall. Mic pre, EQ, and a compressor. But - they have climbed in cost too - Nuvistors.

 

[13engrsapper]

Sorry, I didn't intend to be cryptic. I was thinking that the comment I had referred to ("A popular workaround for the reduced low end of the U47N nuvistor substitution is to replace the output transformer with BV11 type) framed my response as supporting the idea that a BV11 mates nicely with a 13CW4 and would likely be closer to the sound of a VF14/BV08, especially in reproducing low frequency content. That is to say, when a person makes the decision to replace a VF14 with a 13CW4, they do not get optimal performance (at least as per my experiments). It's necessary to change the operating points of the tube - not in the same way that was suggested by Neumann at the time - and then they will still have to deal with the handshake between the 13CW4 and the BV08. The BV11, with its higher turns ratio, again, as per my experiments, will be a better overall approach to retaining as much of the original character of the microphone as possible.

I realize that my ears and musical taste might be more sensitive to particular sonic shifts that occur when changing tube, operating points, and transformer than someone else's ears and taste. By this I mean that I might want to retain some quality in the low end more and be less concerned with the top octave, whereas someone else might be just the opposite. This fact has been part of the complication of trying to fly a U47 without a VF14 since those tubes became very hard to get. There doesn't seem to be any single approach to retro-fitting a U47 that a majority of people agree maintains the greatest degree of similarity between how the mic used to sound and how it will sound when the circuit is significantly changed. So, everyone picks their approach, based on parts availability, costs, their preferences in sound, etc., and takes their best shot at coming out as well as they can. (Maybe we should also talk about how all of the original M7 capsules are coming apart after all these years and this is very significantly changing the sound of the mics).

Relative to the low frequency response of the stock U47 (as opposed to one with a 13CW4 nuvistor in it), my tests showed that in a stock U47 the resonant bump that is caused predominantly by the interaction of the output capacitor with the transformer occurs just at or very slightly above 20HZ. This is part of the reason that some folks have made statements like: "The U47 is different than other mics. If you put a smaller output capacitor in it, the bass actually increases." Well, in a sense, that's true, because a smaller output cap brings the resonant bump higher up into the the audible region, so it kinda does sound like it has more bass. However, if you look at frequencies below the new resonant bump, you'll see that they are in steep decline, because they're now below the passband of the output cap. Most people listening to most music would be likely to hear "more bass" from a bump at 30HZ than one at 20. This is why using a BV11 with a tube OTHER than a VF14 might sound more like what a stock U47 sounded like.

I happen to be working on a "new" mic build that uses a Cinemag BV11 clone and I'm getting to know the characteristics of that transformer, which so far, I'm pretty impressed with. My goal is not to build a U47 clone. I'm wanting to go in the direction of an M49, so my final landing will be somewhere different than where a BV08 would take me. But I'll attach some screen shots that might be of interest. I won't have an original Neumann BV08 in these shots, but I'll include an AMI T47, a Crimson 2766 (BV08 clone), a BV08 clone by Andreas Grosser, a Cinemag 2481 "NiCo" (a transformer that I like the sound of very much), and the Cinemag BV11 clone. In fact, I'll add some decent, but physically smaller 6.5:1 transformers to the image collection to partially address Abby Road D Enfer's response to my comment about the effect of small physical size of transformers (above). In am loathe to go into my '57 Telefunken long body and disconnect its 66 year old wiring to run test signals through the transformer, though I would really like to see exactly what it would look like. If anyone has such a thing, please let me know! Maybe someday I'll have the conviction and necessary resolve to go into my Neumann U48, which has a BV08 that was re-wound by Oliver Archut using the original (vintage) laminations. That would probably give me a pretty good sense of what's going on inside my U47's transformer.

These shots of my scope are a bit blurry due to the florescence of the screen. It's easier to see details when looking at the scope than when a camera creates these images. The transformers are being driven at 5.5VAC (because .25V off a capsule comes out of my Mu 22 test circuit as 5.5V). You'll see that the 10KHz shots are square waves and the low frequency shots are sine waves.
GAD, I SEE THAT THESE SHOTS DO NOT SHOW UP IN THE ORDER I UPLOADED THEM. SORRY, YOU'LL HAVE TO HUNT AND PECK A BIT. Note: for the AMI T-14 I didn't bother with 20HZ. Things were going south too fast. Also, I started at 40HZ with the "Chinese Junk" so you could see how far up in the spectrum it was failing (visible on my scope up to 60HZ).

I had a nice chat with Dave from Cinemag some time back, he said I would come work there anytime, lol. Anywho - we were chatting about tone, vintage transformers - vs new etc. I asked if it was the materials or construction or a combination that made newer stuff sound different than vintage - Dave says "or it may be that we just can't make transformers that bad anymore" I love Dave.

 

[rock soderstrom]

I did look at the Soviet "equivalents"

Yes, there are still plenty of them for very attractive prices. I haven't tried any yet, but I think they're not bad either.
Someday I'll test a few of them.

let's load up that pallet with all of our US tubes. lol

Arrgh, don't buy them all. Someday I'm going to kick myself for promoting these hidden treasures. Doug, you are guilty too!

But I'm already well equipped.

 

[13engrsapper]

Yes, there are still plenty of them for very attractive prices. I haven't tried any yet, but I think they're not bad either.
Someday I'll test a few of them.

Arrgh, don't buy them all. Someday I'm going to kick myself for promoting these hidden treasures. Doug, you are guilty too!

But I'm already well equipped.

You are safe for now - we have a bunch of money tied up in new components for a small production run. I feel bad for my business partner. I never buy what we need... It is usually 10-100 times what we need just so pricing starts to fall in line.

Though we are VERY short of tubes right now.