U47 hand wired with VF14 and BV8

[zebra50]

Thanks for such a detailed picture... So those M's are REALLY visible... I don't think any of these were M's then... a few had an N underneath it, but I have not seen a giant M stamped on any of the pictures they have shown.

There's one on ebay at the moment, with pictures, item number 330391611906 .

Wasn't there a thread over at Klaus's about fake VF14 and related valves? Forum seems to be down at the moment but it's worth checking before you part with your hard owned ££$$€€.

 

[mad.ax]

More about the 1780 Ohms resistor.
This resistor will be dropping 105-36=69 Volts. You need at least a 3 Watts part.
Because of the precision required, and the need to heat-sink those 3 watts to the body, this was built in-house by Neumann. Definitely not an off the shelf part.
I don't know if it is an original one cause I don't see the usual mica layers, but attached is the only pic that I have found (on saturn's website)

You need good thermal conduction for proper heat-sinking, and of course electrical insulation. This was done with mica.
Heat-sinking is not as much necessary to protect the resistor itself (you could use a 10W part and forget about it), but to protect the transformer from excessive heat.

The best way is probably to DIY this resistor by winding resistor wire. Hint: Old toaster can provide good material for the support. Perhaps even the right wire if you are lucky!

Axel

 

[mad.ax]

Here is what it looks like on a very old U47 (serial 186, from jogis-roehrenbude 's website).
You can clearly see the mica insulation.

Also, note the Siemens (instead of Bosch) capacitor, a dual 1µF in a square box, and the vertically mounted BV8...

Axel

 

[rodabod]

About the 17K8 resistor...
This is the problem with that supersonic schematic... R4 is written: 1780Ohm

My apologies! I'm sorry for that. The funny thing is, I actually have a U47 test circuit sitting next to me, but I'm using a variable resistor for the heater voltage-dropper, so couldn't remember the value.

 

[zebra50]

Wasn't there a thread over at Klaus's about fake VF14 and related valves? Forum seems to be down at the moment but it's worth checking before you part with your hard owned ££$$€€.

Found it...

http://recforums.prosoundweb.com/index.php/mv/msg/22206/0/0/0/

 

[speakercoil]

I swear every time I look back at this thread I find better, and better information... This is all stuff I couldn't find in other threads... Everyone seems concerned with only the tubes or moding the mic... Amazing info.

Axel: OMG... Thank you for the photos those are amazing... Also thanks for the info on the resistor. I think I will just have it custom made, because it will probably end up being better than one I make. Also great to know about the insulation. God it would have sucked to burn out the transformer and have to spend another 350 bucks on a new one!!!!! 

Also it's great to know about the wattage... Any other specific wattages used on different resistors? I just assumed they were all going to be 1/2 watt, but now I am starting to doubt that. I normally go over the wattage required anyway... Typically double.. So if it's 1/2 I got 1, if it's 1 I go 2... etc... I like to build things like a Brick Sh*thouse. Once I build something I don't want to be opening it every couple of months to see why it isn't working properly!

I will check to see if I can find any Siemen's capacitors as well. That might be a little easier than the bosch.

Zebra: Thanks for the link!!!!!

-Grant

 

[speakercoil]

OK... So I just want to confirm all measurements now that the whole 17k8 was pointed out to be misprinted... Since then I looked over the various schematics I gathered and sure enough in some it was labeled 17800 and others 1780... So because of this misprint I wanted to confirm all resistor and capacitor values! I am taking these from the one schematic that had the 1780 correctly labeled... Please correct is wrong.

RESISTORS:

R1 100M
R2 50M
R3 29 OHM
R4 1780 OHM
R5 100K
R6 30K
R7 2M
R8 3M

CAPACITORS:

C1 .02uF 400v
C2 .5 mF 250v
C3 1 mF 150v

This is what I have on that schematic... are these correct? Also what wattage values should I use for the Resistors... Obviously the 1780 has been noted to be a higher wattage. However It would be useful to know if the rest need to be higher than 1/2 watt. I will probably end up doing 1 watt for all of them (save the 1780 ohm) to be safe and build it in an overkill fashion... However it is still useful to know.

It does have a drawing at the bottom showing that  R3,5,6,7, and 8 should be .25W, and that R1,2, and 4 should be .1W. However I am assuming this is wrong since it was indicated that R4 should actually be at least 3 Watt... So I am nervous about trusting these measurements.

Also there is a statement in german saying "all voltage levels statically measured". So I am assuming these would be good areas to test once the mic is completed to make sure the voltages are correct throughout the mic.

There is also a section that says "Modulation (switchable 200ohm / 50 ohm) which I am assuming maybe refers to the cardiod/omni switch?

NOTE: after the .25W diagram it says after MIL... Any idea what this means?
Below the .1W diagram it says OIN 41399... Any idea what this refers to?

OK now to make sure of the pin outs, because I know a lot of people have commented in different threads about screwing up pinouts.

Pin 1 and 2 should be from the outputs of the switch after the transformer
Pins 3,4, and 6 appear to be ground? With six saying "housing" which I assume means to connect it to the mic housing somewhere. Also after pin 4 it reads -A -H which means what?
Pin 5 comes from the meeting point of R6, R7, and R4

So those are my new slew of questions for all of you... As you can tell I want to leave no stone unturned going into this. I have been researching siemens NOS capacitors and they are turning up all over the place which is awesome... Now I just need to do a little more research and figure out what series of capacitor by siemens they were. If I can't I will judge by looks.

Thanks everyone again... It's been really useful so far, and not just to me but to someone else I know who is embarking on this same quest (though he is going the EF14 route).

-Grant

 

[speakercoil]

OK!!!! So looking at the diagram I just realized that switchable thing I was looking at cannot refer to the Omni/Cardiod switch, because that is listed at the beginning of the circuit (which makes WAY more sense)... However I would have been surprised to have seen a lead running from the base of the mic up to the switch at the top... Especially considering other mics have the switch actually on the power supply.

 

[speakercoil]

Ok looking closer...
C2 might be .5uf
and C3 might be 1uf

If this is the case I am happy to report I found a 1uf NOS siemens capacitor!

it's hard to make out because these are poor quality.

-Grant

 

[speakercoil]

so I believe I found an almost exact match on the 1uf siemens capacitor...

 

[speakercoil]

Ok ok ok... I know I am spamming this post right now... But I have one last question...

Axel:

As far as that heat is concerned... How is it mounted in there. Your picture makes it look like there is almost a slot for it to fit into... Or is it just kind of shoved in there and attached to the body somehow? Also does that wire run through it? trying to figure out exactly what it is touching to act as a heat sync.

-Grant

 

[mad.ax]

When you refer to a schematic, it is good practice to provide a link, so everybody use the same reference.
For instance, I am using this one:
http://cankar.ath.cx/u47/u47.gif

Depending of the year of fabrication, and the type of transformer used, c2 and c3 can be 0.5µF or 1µF.  If you plan to use square caps, note that you need to attach them to the body. You should also take in consideration that square caps means a vertically mounted transformer, thus a specific bracket, and different turret boards. AFAIK the FLEA kit is made for horizontal mounting transformer.

Resistor wattage. There's a drawing for .25W(a square dot), and another drawing for 0.1W(a band). BUT there's NO drawing for r4.
So, all the resistors with a square dot are .25W, the ones with a band are .1W, and the one without any marking must be something else right? In this case, r4 needs to be 3W if properly heat-sinked.

I guess that MIL is another norm, just like DIN41399.

Now I don't understand why you would like to use original components, down to carbon comps, and decide to “upgrade” to bigger wattage? Especially since we know that a gig part of carbon comp mojo, is the fact that they drift with temp. If you change the temp by upgrading the wattage, there will be less drift, uh?

There's no switch after the transformer. There's a dual secondary. You can hardwire it for 50 or 200 Ohms operation.

There's no slot for r4. There's some kind of metal bracket which I guess is hold by the body screws on both side. This bracket's purpose is to press the resistor against the body (for good thermal conduction), and also to provide some heat-sink for the internal side of the resistor. What the picture doesn't shows is the two mica layers that provide insulation between body and resistor, and between resistor and bracket.
AFAIK, there's no suck bracket in the FLEA kit. One more thing to DIY.
As for getting r4 “custom made”, I don't think any resistor manufacturer would do it, unless you order 10000, but there are not enough VF14 left for such a market, and it would cost you much more than a mint, real, original, and genuine NEUMANN U47!

Have a look here:
http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Neumann-Mikro/U47/U47.htm
There's a lot of detailed pics that may help you to understand more about the internal construction of U47.

Axel

 

[speakercoil]

Sorry I should have just posted a pic of the schematic I was looking at... Which is basically the same one you posted. However in poorer quality (it's actually a scan so there are creases and the type face is faded). As for the square cap changing it to vertically mounted (the transformer that is), that puts a big frown on my face. I guess that means I will look for a round one. It would be easier to not tinker with the housing too much. As for the carbon comps, you are correct. The only reason I wanted to go with a bigger wattage was for safety, and because I wasn't 100% sure of the wattage ratings. I probably will keep the 1/4 watt as they should be, but I may raise R1 and R2 up to 1/4 watt just to be careful. To add a slightly unique mojo I might change those from carbon comp to one of my favorite type of resistors which are NOS Shinkoh Tantalums... However I may keep them carbon comp. We will see.

I was exhausted after a long day of work, so not seeing the dot is why I thought R4 was a part of the .1Watt group! However I missed the fact that is also doesn't have a line.

There is a company that does custom 1 offs of wire wound resistors. A guy over at gearslutz had them made, I just need to find the thread. He only ordered 5 and said they weren't super expensive... Like 3-5 dollars a piece or something. Which yes for a resistor is kind of absurd, but considering this is kind of a unique resistor and obviously very important I will probably shell out the cash.

Thanks for clearing up the Dual Secondary for me. Now for the question of how I should hardwire it... 50 or 200 ohms? It doesn't specify?

Do you think I am going to have to DIY that heat sink or does anywhere sell replacements for old U47's? I have a feeling that is going to be DIY.

Alright so I am coming along... I have my components list written out and once I source everything I will post it for double checking if anyone wants to.

Axel you have been of particular help on this project and I have to thank you for that a thousand times. When I start constructing this and making videos I am going to give you a few shout outs.

The part I cannot decide on is weather I want a PVC Capsule or Mylar... I know the trade offs... PVC will change radically every year and eventually breakdown for good. The Mylar will last longer, but has a different sound. For originality I should go with PVC... However to keep my mic from crapping out every few years, I should go Mylar... So I know the ups and downs, I just need to make a decision.

If all goes well I am going to order the BV8, capacitors, and resistors in the upcoming week. Then will come the RV14 (regardless of using a VF14, I am using this for testing purposes, before I endanger 2k of my cash!). Then the body and capsule, which will take a little saving up.

Thanks again everyone!
-Grant

 

[bernbrue]

BV8 transformer replica by Peluso, might be interesting:

http://cgi.ebay.com/BV8-Transformer-for-U-47-Clones-Neumann-refurb_W0QQitemZ310110387713QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item483404fe01

regards
Bernd

 

[speakercoil]

Thanks for the link, but I am already sold on the TAB Funkenwerk BV8... It is the same one used by Wunder, Telefunken USA, and Wagner for their clones... So if they all leaned toward TAB instead of competitors it must be for a reason!

-Grant

OH... and Axel... AMAZING link on the pics inside the body... that will help a lot!

Also I just contacted Mills Resistors (because I know they make some wire wound) and asked if they have any 3Watt+ 1780 Ohm resistors... If I can find already manufactured wire wounds, I might as well just get those. Also Mills has a great reputation.

 

[dangeruss]

I'm with Grant here when I say this is so much awesome information. You guys are all inspiring and brilliant. I'm the other dude Grant spoke about embarking on the same quest, Russ. If you like you can check out http://makingmyu47.tumblr.com on which I'll be chronicling my learning and building process over the course of the project. Hopefully Grant will make a few guest appearances with his project as well.

I have one additional question. I'm going the EF-14 route and to my understanding the only modification that needs to be made is to place a dummy load consisting of a capacitor and resistor just before the heater, connected to ground, to get it down to 4.95V instead of 36V. Do any of guys have any information about that? i.e. whether that's the full extent of the mod required and if so, what value capacitor and resistor I'll need in order to divert the 31.05V difference.

Any information would be greatly appreciated!

 

[rodabod]

I have one additional question. I'm going the EF-14 route and to my understanding the only modification that needs to be made is to place a dummy load consisting of a capacitor and resistor just before the heater, connected to ground, to get it down to 4.95V instead of 36V. Do any of guys have any information about that? i.e. whether that's the full extent of the mod required and if so, what value capacitor and resistor I'll need in order to divert the 31.05V difference.

You kind of have three options here in my opinion: 

1) massive 105V supply like original but more current, 2) independent 5V heater, but dummy 105V filament supply for bias, 3) small 105V supply with small 5V heater which doubles as a bias supply.

You need to consider how the circuit works, and the implications PSU-wise in order to decide. Remember that the EF14's heater sucks around half an amp at full heat.

By the way, I'm still completing my underheated VF14 curve tracing tests which I will compare with EF14s at different temperatures, but as I understand it, around 5V is said to be a reasonable figure (and remember you may get reasonable voltage drop in your cable at these currents!)

Roddy

 

[speakercoil]

Hey russ,
Whenever we get together I will burn you a disc full of all the images and schematics I have gathered. A lot of amazing closely detailed pictures of the soldering, etc... Also I have some schematics for different EF14 mods in there somewhere.

Also for everyone else... I just saw a ton of NOS Bosch Capacitors thrown on e-bay today, but none of them seem to be of the right values! I got really excited and then really let down.

-Grant

 

[speakercoil]

Another capacitor question...

So the 1uf I am assuming is paper in oil... What are the others? Are there any styroflex, silver mica, or polystyryne caps? Just curious, because if I cannot obtain the proper brand of capacitor it would be nice to get the proper type. I can't believe I asked this about the resistors and not the capacitors!

-Grant

 

[zebra50]

Remember that the EF14's heater sucks around half an amp at full heat.

Indeed. Dropping off about 100V at, let's say an underheated 400 ma, ballpark, R=V/I gives 250 ohms, W=I^2R gives 40 watts... That's one big resistor and one hot microphone.

Have a look at the MK7 mic design for interesting options on the tube bias.