Reissmann Tube Mics - schematics & ideas

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zebra50

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Joined
Jun 4, 2004
Messages
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Location
York, UK
Hi!

I have some old Reissmann tube mics to play with. Bit of a mixed bunch. Tow are bottle mics and two are sort of fat stubby things. All the mics are currently transformerless Hi-Z outputs. I understand that they have come from a radio station, via a museum.

RMic1234.JPG


One of the bottle mics has an EF12 tube, the other an EF86 (But in an EF12 socket via an adapter. The small mics have EF86 and EF806. They each have different circuits which I am still tracing out. The capsules look OK.


RMic1221.JPG


RMic1229.JPG


The power supplies are part of bigger tube mixer - amplifiers - big heavy 150W things with 6ohm, 20 ohm and 400 ohm outputs. They have horrible DIN sockets. The heaters are AC, I think.

RMic1235.JPG


I'm trying to decide what to do - whether to keep them as original as possible, or to build completely new power supplies (similar to the G7), or to adapt the current amp supplies. Or make brand new circuits around the EF12 and go for transformer matched balanced outputs. Or something else completely.

What would you do? I'd love to hear your ideas before I start hacking.
Cheers!
Stewart
 
[quote author="zebra50"]
I have some old Reissmann tube mics to play with. One of the bottle mics has an EF12 tube, the other an EF86 (But in an EF12 socket via an adapter. [/quote]
It is good to still use idea of transformerless mic.
How tubbe is connected?? , if as common plate,
use shielded cable to the mic and two signal wires.
One connected to the cathode and second to the ground
in the microphone.
Next circuit can be normal differential amp.
You must have 4 wire shielded microphone cable,
heat, plate, cathode, mic_ground and shield.
Mic_ground is connected to the shield in the mic and is kind of
hum-bucking.
"Power" ground to the mic will be trough cable shield
xvlk
 
Try to convert the one with EF12 to something like this:


m501.jpg


m502.jpg


This is the history of these mic's. (It is from eBay...)
These are Neumann M 50 prototypes developed by IRT acoustic german institute.The M50b schematics I got from Neumann GMBH Berlin have the IRT mark, not the Neumann one.Some previous schematics the NWDR mark. The M50 project didn't born in Neumann, but they developed the IRT research under NWDR request.Neumann was the factory that did the serie production along the time. The project began in 1948 and these ones were manufactured as prototypes in 1950. They come with two Neumann K53 capsules plus a gold sputtered small diaphragm thirth spare capsules, as the one installed in the older and rare M50 microphones. Neumann GMBH got the project, modified it and made the world famous M 50 installing the sphere mounted capsule in the M 49 microphone body. I did several researches to get a few of info about these microphones. Mr. Jim Webb, one of the most important mic collector worldwide, never saw or had them. They have a very particular tone, very close to the M50, probably sweetest and more brilliant. They come with original IRT manual copy - Set of not shown cables. Rebuilt double power supply for matched pair operation (Not shown), single Schoeps power supply internally rebuilt for single microphone operation. Three capsules (two nickel ones and one gold sputtered in a Neumann box).Showed boxes. This pair is an incredible piece for a collection as an incredible pair for great recordings.They have the same connector and size of U 47 48 mics so it is very simple to locate a shock mount to hold and calibrate mics on location.

It appears that EF12 tube was more common then than VF14 ...
 
Thanks for the information so far. Nice looking Siemens mics, lampas.

The circuits are plate follower tyes. One bottle mic is very standard - EF86 wired as triode, but the output cap and plate resistor are in the power supply. The cathode is grounded directly. The EF12 mic is a bit more complex - seems to be wired as pentode.

The two small mics have dual capsules, although it looks like only the front one is connected. Unfortunately both have slightly worn or damaged capsules on one side so I may flip them over and just try using the good sides.
 
hi stewart-

do the mics work at all right now? they sure look cool. If you are using them to make a recording and not collecting them for a museum, if it were me, I would leave the mics alone to start and rebuild the power supplies. Ive done this with most of my tube mics and have always heard an improvement with a new supply. Im completely not a vintage mic snob though, I look at these things as tools and am more than happy to improve performance of an aging power supply. I would do that first and then get into modding the mics if I still wasnt happy, but usually a new suppply will do pretty well in tightening the bottom end , Ive done that with a few of my mics and they sound "snappier" with a new supply in all cases.

dave
 
Hi Dave,
That's a sensible suggestion, and something i was thinking over. I want to use the mics for recording and I don't really like the idea of this huge tube amp hogging all that power.

I'm just building some test cables for the mics now to see if they work OK with the existing supply.

The amp itself is superbly engineered actually, (apart from the sodding DIN plugs). Although the heaters are AC, they have a pot to adjust the balance wrt ground so you can minimise the hum. Pretty sensible.

:thumb:
 
Stewart,

I'd leave them as they are, to preserve their "historical" value--the reason I don't do anything with my Russian mics. Bring them to more or less sounding condition, then if you really want to try transformer--put in-lines, in close proximity to the mic body and see what do you say. It would be a nice trick also with small condensers, where there is not enough room in the body for a healthy sized trafo.
 
I'm with Marik; it would be a shame to mess with these. An inline transformer is a fine idea and if you want an upgraded power supply/amp, put the old one up on a shelf and build a new one from scratch.
 
[quote author="zebra50"]Thanks for the information so far. Nice looking Siemens mics, lampas.

The circuits are plate follower tyes. One bottle mic is very standard - EF86 wired as triode, but the output cap and plate resistor are in the power supply. The cathode is grounded directly. [/quote]

What to make power supply as current mirror ?
Use anode resistance in power supply is inefficient due cable capacitance.

xvlk
 
Thanks again.

3 of the 4 mics (2 bottles and one small one) work OK with no changes & pass audio with the existing supply. Sound quite good but definitely will be 'character' mics rather than hi-fi. One of the small ones is sick & needs attention. The supply/amplifier is very noisy (hum), and also spits out 7V AC for the heaters which I don't like.

I think I'll go the route of a new, regulated, PSU and keep the mics as close to original as is sensible. The DIN connectors have to go! - they don't look original anyway so I feel justified in finding another option.

Will keep you posted.
Stewart
 
I traced out the schematics of the mics - they're all grounded cathode amplifiers - three have the plate resistor and output cap in the power supply, one does not.

This is the big one with the EF12... (heaters omitted)

RMicSchem.gif


None of the mics seem to have cathode resistors. Is that right? I haven't worked with circuits without cathode restors before. I can't see them in the power supply.

Two of the mics have 100 Meg from input grid to ground. I thought it was usual to have a cathode resistor in this case so that the grid sits at some -ve voltage with respect to the cathode?

Or am I just confused again?

Cheers!
Stewart
 
It's normal to use no cathode resistor if the grid to ground resistance is high. ECC83s were often used with 10M grid resistors in radio circuits. The leakage current will develop a negative voltage at the grid.

Best regards,

Mikkel C. Simonsen
 
Hard to tell as I only have one power supply at the moment. I'm building a new PSU with adjustable voltage DC heaters whoch will run pairs of mics.

But I doubt the two bottles will be very close. They have different tubes, different circuits, and even slightly different capsule designs.

I'll let you know.
 
i've got a REISSMANN tube mic as well. (been looking for other owners for a long time... :) )

it uses an EF12K tube. and i'm pretty sure the schematic posted here is close to the one i have.
i have a few pics of it - but nowhere to upload it.
and the PSU is just as old, looks very original - but i'd like to mod it to have a Lo-Z balanced output.

any help would be great.
is it just a matter of buying a transformer (7:1)? or what?

right now the mic is Hi-Z unbalanced. it sounds great and i still kick myself for selling the other REISSMANN identical mic i bought way back (bought the two of them the same day!)

any help would be great.
 
A 7:1 transformer should sort you out.

Search for "reissmann" and read everything available. There has been a fair amount of discussion.

I am working on one just now.
 
why not just use something like this:
http://i6.ebayimg.com/01/i/02/df/31/f6_1_b.JPG

no soldering etc.. needed :)

but seriously - wouldn't this be enough?
 
Technically, that would probably be enough to act as a step-down transformer, but...... It would probably sound like ass.

Maybe worth a shot though. It would be handy to know the turns ratio to calculate what the output impedance would end up being.

By the way, is you Reissmann slightly omni-directional?

I've mounted my capsule temporarily in a cheap condenser mic and found that it is almost omni and not very cardioid.
 

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