[rmburrow]

RFI elimination in a condenser microphone may not be a single step solution.  This assumes you are using good quality cable between the mic and power supply, and cable from the power supply audio output to the preamp, with no wiring or grounding errors.

Bypassing with capacitors can affect the sound, especially if applied across a high impedance.  You may want to try a single ferrite bead at the tube grid connection.  This should reduce RFI before the grid.  Make sure the headbasket and other metal components (connector shell, etc.) are  grounded electrically to the mic body.  Check with an ohmmeter.  RF from a poorly grounded headbasket (antenna) will couple to the high impedance capsule.  The 560 pF cap alone may work across the secondary of the output transformer...but a ferrite bead on each side of the output transformer secondary may work better.  Bad RFI cases may require bypassing the output transformer secondary with capacitor(s) and ferrite beads.  Also, make sure the audio from the mic goes straight to the XLR connector with no components to ground.  (Don't need ground loops.)  My $0.02 worth...

[e.oelberg]

but why don't you read what I wrote: I said I solved the radio issue, I just don't like the sound  of the lowpass and my question was how high can i put  the lowpass and still get rid of the rf noise

[Murdock]

but why don't you read what I wrote: I said I solved the radio issue, I just don't like the sound  of the lowpass and my question was how high can i put  the lowpass and still get rid of the rf noise

yeah, and he gave you some hints on how to solve the radio issue without the lowpass which you said you don't like, right?
And why not try yourself how high you can go? Just experiment with different values until you're satisfied.
Or try the other solution rmburrow offered you.
Or did I also get you wrong?

[e.oelberg]

you are right ! I'm sorry, acctually the first time i missed the tone on this forum, my fault.

[RuudNL]

e.oelberg Good to read that you are happy with the 6S6B in your microphone.
I used a couple of those tubes and the quality seems very consistent.
Noise is low, which is a good thing. I prefer them over a 5840.

[e.oelberg]

Hi Ruud

I'm very happy, I ponder of kicking out an EF86 in another mic and try a 6s6b instead, very quiet, not very microphonic. The  m49oid mic is my favorite mic in my collection. I have no 5840 but ef732 and I think the russian tube is much better, but than again I didn't do a direct comparison and there are always so many things to consider.

[e.oelberg]

Ruud !

did you compare it to a ac701 ? My guts tell me there can't be much of a difference in terms of noise am I right ?
Sound is always difficult to describe..

[RuudNL]

Unfortunately I don't have the M49 with the AC701 here anymore. (It wasn't mine.)
But from what I remember, the self noise of the tubes is in the same order.
That is: at a very low level!
I already replaced the (1/2 used) ECC83 in another tube microphone with a 6S6B.
That made a tremendous difference in self noise. In fact: the microphone is now useable! 
I ordered 25 of those 6S6B tubes, and the variations in self noise are in the range of only 1 dB. (I have tested them all!)

[justinheronmusic]

First time microphone builder here:

 Can anyone help me out with how to connect the CM-6511 transformer?

 Do I tie red and orange together, and then blue and violet together?

[KrIVIUM2323]

Primary are : Brown , red; orange, yellow,
Secondary are : green, blue; violet, grey.
You should have primary and secondary each serial connected so:
Red and orange tied together, blue and violet tied together.

Primary 'input' is then Brown, yellow go to ground, secondary '+' output is green, '-' is grey.
The dot in cinemag's schematic give you indication about polarity.

[justinheronmusic]

Thank you so much! That is a huge help.

Also, I found the tube pinout connections, I thought I would post them here for future accessibility.

5840 Tube:

Pin 1 to FGRID
Pin 2 to K
Pin 3 to H+
Pin 4 - Cut
Pin 5 and Pin 7 Tied together to A
Pin 6 toHG
Pin 8 - Cut

[Rlucas41]

How do you wire the 6S6B tube? The pins i mean...

[TillM]

Pin 1 to A
Pin 2 to H+
Pin 3 to HG
Pin 4 to Fgrid
Pin 5 to K

[Rlucas41]

Thanks TillM,
I have just ordered some 6S6B tubes, I have built two D49c's and both sound great, curious if the 6S6B will be a little quieter tube...

[Nele]

I'm about to start building an M49 and want to use the 6S6B tube. Is there anything else I need to adjust from the standard schematic besides the heater voltage? Maybe different transformer?
And where did you guys get the tubes?

[RuudNL]

Probably only adjust the cathode resistor to get the bias in the 'sweet spot'.
I bought 25 pcs. of the NOS 6S6B tube in Russia. (And they are all excellent, tested them all.)

[Nele]

Probably only adjust the cathode resistor to get the bias in the 'sweet spot'.

Thanks! Is this done by ear or can I use some kind of formula (sorry for the newbie question..)

I bought 25 pcs. of the NOS 6S6B tube in Russia. (And they are all excellent, tested them all.)

Did you buy them online? The only source I can find is in Bulgaria?

[vinylwall]

Just in case anyone is interested, I have one of my D-49's up for sale (fully assembled).
https://www.ebay.com/itm/183889998100

[Rlucas41]

Howdy folks, need some help wiring a 5703wb Raytheon tube in one of my D49’s.
I have the datasheet denoting the lead next to the red dot but its numbered: 1(red dot) 3_4_5_6

help me please

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