Reissmann Tube Mics - schematics & ideas

[cedric]

omni directional?
yes definetely.

i can't take the mic apart (the top part) to actually check out the capsule - feels like someone super-glued it together. darnit. so i've never been able to check out the capsule.

the capsule (dynamic element) that was installed in my Electro Voice V2a - looks like a large diaphragm though. i love these old weird mics i have.
i never wanna hear another 57 on a guitar cab anymore!!

 

[Brown Note]

I just picked up one of the smaller, non-bottle Reissmann mics (the one on the left in the pic at the beginning of this thread). I believe the model number is MR51.

I drew up a schematic:

http://www.twin-x.com/groupdiy/displayimage.php?album=119&pos=0

What purpose does grounding grid 3 serve?

I plan on building a power supply in the next couple weeks using:

-100k plate resistor
-2.2uf coupling cap
-Edcor XSM10k/150 output transformer

Any suggestions for the B+ voltage?


-Ben

 

[burdij]

Grounding grid 3 and returning grid 2 to the plate causes the pentode to act as if it is a triode. Hopefully, there is some circuitry to return the cathode to ground. The circuit, as drawn, will not work. The cathode probably is the output (the circuit acting as a cathode follower) and would be coupled to the output transformer with a capacitor, but it would also need to return DC to ground through a resistor. The B+ can vary since it is a CF, but the voltage is going to determine the polarizing voltage on the capsule. Therefore it probably shouldn't go above 100VDC. The M7 experts in the crowd should know what the max is for this type of capsule. 47 Megs is not going to be high enough as a polarizing resistance. The typical range for an M7 in this type of circuit is 100-200M or higher. Same with the grid resistor. 100 M (2x 47M) will work but 200M or higher would be better.

 

[Brown Note]

Well I wouldn't bet my life on it, but I'm as close to certain as one can be with this schematic. There are only 6 components, a tube, a capsule and the wires in between. I've checked and re-checked it...and re-checked it. I could be wrong on the resistor values because I don't have a meter that measures that high. All 4 resistors are marked with 47M10, which I assumed to be 47M 10%.

After drawing the schematic I didn't think I could work either, but it does. I breadboarded a supply with stuff I had laying around. I think it sat at about 105v loaded. The output copuling cap is connected to the same point as B+. The signal was pretty hot considering the the plate was driving the 1:2 transformer on my console input.

 

[Brown Note]

Of course, immediately after that post I had to do a re-check. The cathode is grounded. I don't know how I missed it the 6 other times

Now to fix that schematic.

Thanks!

Ben

 

[Gus]

Down to 8 megs has been used grid to ground so 47megs can be corrrect

One of the ela m251 schematics on the web has a 8 meg grid to ground another 30meg IIRC.

 

[burdij]

Well, if the cathode is grounded, that changes things, I guess. Its not a CF circuit. The problem with that is that the capsule polarizing voltage is going to be dependent on the quiescient point of the tube. It would be better to run the polarizing voltage from a constant voltage source, in other words, from the B+ side of the plate load resistor. The grid is also going to be near zero volts with no cathode resistor. Typically its about -1 volt in this type of preamp. That will also affect the operating point of the tube.

 

[skoracki]

Hello every body,
I'm trying to re make this thread alive.
In Fact I think this microphone is a good opportunity to have a good tube microphone.
I've read all comments of this topic.

Does anyone use this mic now ?
Zebra 50, you said you've make a new PSU for it, could you send me a schematic ?
I've got also one Reissmann MR50 bottle mic, but without any PSU.
I've found an output transformer for to get in, but nothing about how to make a PSU.

Maybe this work interest many guys who found this beautiful mic and would want to get it alive.

Many thanks for all

 

[zebra50]

Hi!

This was some years ago! I don't have an exact sketch around!

One problem is the three of these mics that I've played with have all been different. If you look at the schematics on my website (www.xaudia.co.uk) you'll see at least two different circuits!

Another issue is that the mic does not contain an output transformer, so you'll need to run

They can sound nice but were designed for PA applications / speech so they don't have much of a low end.

Some PSU ideas soon!

 

[zebra50]

OK, having looked at my schematics again, you need about 105 V for B+ and 6V for the heater. I think I used a 7806 voltage regulator for the heaters and a resistor-capacitor network to make the B+.

Some ideas...

1.  Build something like the G7 power supply from www.gyraf.dk. That will give you a good starting point. You don't need the pattern control section so that will save you some work. And you'd need to experiment with the resistors for B+ to drop the voltage down to 100-110V.

2. Or you could build a power supply like the one in the 'Royer' mod. That gives the right voltages with very few parts.

3. Or adapt one of the Neumann CMV power supplies that go cheap on ebay all the time!

Now unlike most of the tube mic projects here you'll put the output transformer in the power supply. Actually this is very much like the Royer 'small' tube mic project in Tape Op. That might be a good place to start:

http://www.diyfactory.com/projects/royerproject/royermod_2.pdf

That project is for a cathode follower, so uses something like a 2:1 transformer ratio. For the Reissmann bottle mic I used a 7:1 Sowter - it was a reversed mic input transformer, probably model 4935. But there are lots of other options - Lundahl etc.

http://www.sowter.co.uk/

 

[Studio Mollan]

I just bought two reismann mr51 and the sound surprisingly good! Got them of eBay with a custom psu incl output transformers.
Is there a way to mos them to cardoid?
/
Emil

 

[zebra50]

The MR51 has a dual sided capsule, with each side cardioid-ish. The big old bottle mics had an omni capsule, but the shape of the head gives some attenuation to the rear.

So long as only the front of your capsule is connected then you should be cardioid already. What do your ears tell you?

 

[Studio Mollan]

Thanks for your reply!
I checked inside the microphones today. M7:ish capsule with no connection to the rear membrane. It should be cardioid but sounds somewhere in between. Using the pair x/y gives minimal stereo information. I detect a slight proximity effect when up close to it. Nothing like other condenser cardioids but also not like an omni. Pretty strange and although I'm ready to settle with them the way they are it would be fun to know why they are behaving like this. I read in a different thread that someone else had the same experience.
They sound good though and I got them cheap so I'm still very happy!

 

[Studio Mollan]

Wrong.
Actually I read it in THIS thread.

 

[zebra50]

Hi!

The pattern of the mic depends on the backplate design - as I understand it, deep and through-holes make it more cardioid / figure 8, whereas shallow holes or no holes at all make it a pressure-mic (i.e. omni). It is a fine art, and more complicated than that, but the balance and types of holes control the pattern. The pattern will also be frequency dependent.

So I guess the Reissmann capsule simply has a lot of omni character. But if it was intended as omni then don't know why it would have a second skin at the back - it seems redundant.

My hunch is that it was designed to be cardioid-ish, but poorly executed.

You can't really change the character without taking off the membrane (bad idea), and drilling new holes (probably won't do what you think unless you are skilled in the art).

The earlier Reissmann bottle mics have a 'proper' omni capsule with only shallow blind holes. I know this because one of mine was trashed so I could have a good look!

Cheers!