Delta Sigma

So this will be my first tube mic build and I would love any opinions or advice.

My current plan is:
-Chunger’s CU-49 body
-Collective Cases PSU box
-Dany’s D7 capsule
-6S6B-V
-Cinemag CM-6511?

I wanted to find out if I need any alternate components if I want to use a 6S6B-V over a 5840. Is it still wise to use a Cinemag CM-6511 with this tube?

Also, I am still undecided on the b or c version and would appreciate any thoughts.

Thank you in advance!!

Another vote for Moby's BV.11. I haven't heard Dany's M7 but the reviews are extremely positive. The 'B' version kicked my ass with hum. I eventually got rid of the hum but it took a long time. Play it safe and build the 'C' version.

You should be able to get 6S6B and 5840 for relatively cheap. Try both. Be careful in switching tubes. Use a properly sized tip and a good mechanical desoldering pump (like OK industries). I have a Hakko 808 but I don't use it in most sections of mics because it's too hot and the tip is too big.
Neil Fitzpatrick


egroys

Another vote for Moby's BV.11. I haven't heard Dany's M7 but the reviews are extremely positive. The 'B' version kicked my ass with hum. I eventually got rid of the hum but it took a long time. Play it safe and build the 'C' version.

You should be able to get 6S6B and 5840 for relatively cheap. Try both. Be careful in switching tubes. Use a properly sized tip and a good mechanical desoldering pump (like OK industries). I have a Hakko 808 but I don't use it in most sections of mics because it's too hot and the tip is too big.

You all are amazing!
Great info! Thank you very much for this.

To clarify and summarize:

- I can interchange the tubes without changing any other physical components?
- I should get a nice MP output cap at 1uf 200v (I believe to substitute the 1uF 250volts Vishay on the BOM?)
- Any other substitutions from the main BOM I should consider? I see @purplenoise made a few but the values are the same.
- Which ratio of the BV11 should I be aiming for considering my component selection? I am seeing 7:1 for M49c and just want to confirm that would be good for the 6S6B and 5840?

Thank you all!

You all are amazing!
Great info! Thank you very much for this.

To clarify and summarize:

- I can interchange the tubes without changing any other physical components?
- I should get a nice MP output cap at 1uf 200v (I believe to substitute the 1uF 250volts Vishay on the BOM?)
- Any other substitutions from the main BOM I should consider? I see @purplenoise made a few but the values are the same.
- Which ratio of the BV11 should I be aiming for considering my component selection? I am seeing 7:1 for M49c and just want to confirm that would be good for the 6S6B and 5840?

Thank you all!
Moby offers 7:1 and 10:1 for bv11. I went with 7:1.
MP output capacitors are not carried by mouser, you can find them used or nos on eBay. MP stands for metalized paper and sometimes sellers list them as PIO ( paper in oil). See the pictures it will say MP on the cap.
I used an elna silmic 22uf 10v cap for the cathode...wasn’t very fond of the tantalum sound.
Also I am not using the 8pf mica cap. I prefer the sound without it but you can install it and then disconnect one end to see how it works for you.

Delta Sigma

- I can interchange the tubes without changing any other physical components?

You may have to change the heater supply, I can't remember. If one of their heater currents are different, that may change the range of your heater adjustment.

A good practice with passive power supplies and different tubes is to order a high watt low value resistor to go in series of the heater pot. In other words, if the heater pot was 250 ohm 5w, pick up a 100 or 150 ohm 5w resistor. That way if your heater voltage was too high, and couldn't be adjusted down, you could add the resistor. Another good practice, is to order a couple smaller value dropping resistors. Say 10R and 18R at 2W just in case your heater current is too high and can't be adjusted up.
Neil Fitzpatrick

adrian

hello Delta Sigma!
I saw in a previous post you replaced your AMI BV11r by a Moby transformer,
I'm currious to know why and what was the sound difference?
thank you!  ;)

Delta Sigma

hello Delta Sigma!
I saw in a previous post you replaced your AMI BV11r by a Moby transformer,
I'm currious to know why and what was the sound difference?
thank you!  ;)

To be completely honest, I was ordering another transformer from Moby and I had a couple too many beers and asked him for an invoice for the BV.11!

I originally thought about about replacing the BV11r when I replaced my 5840 with a 6S6B which didn't lack the low end that the 5840 did.

The AMI BV11r sounds perfectly fine, Moby's BV11 just sounded better to my ears. Moby's transformers seem have a nice colour that really shines in high frequencies. I've heard his BV08, BV11 and BV12 and they all seem to have a really nice colour, especially in high freq.
Neil Fitzpatrick

egroys

I don't think Dany's power supply PCB will fit a TPS100. If you build an M49b, you will add a choke and you'll need a big box like Collective Cases' mic power supply chassis.

See Dany's Mouser BOM in the first post for power supply components. Note that he includes optional parts like a Hammond enclosure in the BOM. Don't just add to cart, review the BOM.

Quick follow up! I am going to be going for the 'C' version as folks have recommended. Does this mean I can omit the choke? Is there anything else I can ommit?

Thank you again!

egroys

Moby offers 7:1 and 10:1 for bv11. I went with 7:1.
MP output capacitors are not carried by mouser, you can find them used or nos on eBay. MP stands for metalized paper and sometimes sellers list them as PIO ( paper in oil). See the pictures it will say MP on the cap.
I used an elna silmic 22uf 10v cap for the cathode...wasn’t very fond of the tantalum sound.
Also I am not using the 8pf mica cap. I prefer the sound without it but you can install it and then disconnect one end to see how it works for you.

I went for the 7:1!
Could you quantify the benefits of an MP output cap over the one in the BOM?

Does anybody have any tips for pumping more volume out of this mic? I rebuilt the c as a b, with a new NOS 5840W tube, and the sound is better than it was.

I had to remove the shield connection on one end of the cable to get rid of a PO.

I was fairly content with the mic being better than it was, but after building the EF47, I'm not at all satisfied with this one. I can clip my input with the EF47 at 23 on the input level, but even with double the input gain, the M49b doesn't get enough volume.

Both are using the same transformers and capsules.

Thanks,
Josh

I went for the 7:1!
Could you quantify the benefits of an MP output cap over the one in the BOM?
This is my personal experience and not scientific. I have found the high end to be smoother and more 3D/rounder with MP caps. MKP sound a little harder and more “papery” in the high mids and highs. Every brand though sounds a little different with Siemens, Bosch sounding very neutral and clean and the Russian caps a little “dirtier”.
Plus...m49s and u47s had mp caps to begin with
« Last Edit: March 24, 2021, 01:27:51 AM by Purplenoise »


Does anybody have any tips for pumping more volume out of this mic? I rebuilt the c as a b, with a new NOS 5840W tube, and the sound is better than it was.

I had to remove the shield connection on one end of the cable to get rid of a PO.

I was fairly content with the mic being better than it was, but after building the EF47, I'm not at all satisfied with this one. I can clip my input with the EF47 at 23 on the input level, but even with double the input gain, the M49b doesn't get enough volume.

Both are using the same transformers and capsules.

Thanks,
Josh
Mine with a 7:1 Moby bv11 and 8pf mica cap removed is as loud as my D-EF47 more or less.

Parasitic oscillation?  Have a scope with low capacitance probe to get some idea of the frequency?  Interesting that lifting the shield on the cable "stopped" the oscillation.  I would expect the oscillation would get worse with no heavy shield ground, especially to the mic body.  There may be a ground loop or an inductive loop (even a loop of wire) associated with grounding.  Cold solder joint can cause trouble.  Doesn't take much of a wire loop with a nearby high impedance capacitive circuit to resonate and oscillate at some RF frequency.  You will probably need to open the mic and go in with a scope since the output transformer won't pass RF frequencies.  By lifting the cable shield, you may have shifted the oscillation higher in frequency, upset the operating point of the tube, so the apparent result is decreased audio gain, and the real problem is still unsolved.  If you are using a 5840, continuous twist the cathode and suppressor (g3) leads together to their termination, and likewise for the screen (g2) and anode.  No excessive lead length.  If you really want to do it right, follow the instructions for installing a AC701, including 5 close spaced turns of tube lead (directly out of the tube, for each lead) over a 1 mm drill bit (1/16" works) to provide for heat sink when soldering tube leads so the glass won't crack.  Use a good pair of needle nose pliers and no stress where the leads enter the tube.  The tube must be oriented so the control grid (g1) is closest to input from the capsule.  I assume the tube orientation is incorporated in the kit circuit board...   BE CAREFUL working inside the mic, connect test gear with power OFF, then test with power on; use clip-on probes to avoid accidental shorting, make sure mic power supply is discharged before making changes, set the scope input to AC to isolate the DC from the mic circuits.  Do not clip the control grid (g1) high impedance connection with the scope or multi-meter. Voltages (and scope indications) at the cathode, anode, or the variable polarizing voltage should indicate what is going on.  You may find oscillation in the MHz range.  Low gain anode followers usually work, but will oscillate if conditions are right.

Parasitic oscillation?  Have a scope with low capacitance probe to get some idea of the frequency?  Interesting that lifting the shield on the cable "stopped" the oscillation.  I would expect the oscillation would get worse with no heavy shield ground, especially to the mic body.  There may be a ground loop or an inductive loop (even a loop of wire) associated with grounding.  Cold solder joint can cause trouble.  Doesn't take much of a wire loop with a nearby high impedance capacitive circuit to resonate and oscillate at some RF frequency.  You will probably need to open the mic and go in with a scope since the output transformer won't pass RF frequencies.  By lifting the cable shield, you may have shifted the oscillation higher in frequency, upset the operating point of the tube, so the apparent result is decreased audio gain, and the real problem is still unsolved.  If you are using a 5840, continuous twist the cathode and suppressor (g3) leads together to their termination, and likewise for the screen (g2) and anode.  No excessive lead length.  If you really want to do it right, follow the instructions for installing a AC701, including 5 close spaced turns of tube lead (directly out of the tube, for each lead) over a 1 mm drill bit (1/16" works) to provide for heat sink when soldering tube leads so the glass won't crack.  Use a good pair of needle nose pliers and no stress where the leads enter the tube.  The tube must be oriented so the control grid (g1) is closest to input from the capsule.  I assume the tube orientation is incorporated in the kit circuit board...   BE CAREFUL working inside the mic, connect test gear with power OFF, then test with power on; use clip-on probes to avoid accidental shorting, make sure mic power supply is discharged before making changes, set the scope input to AC to isolate the DC from the mic circuits.  Do not clip the control grid (g1) high impedance connection with the scope or multi-meter. Voltages (and scope indications) at the cathode, anode, or the variable polarizing voltage should indicate what is going on.  You may find oscillation in the MHz range.  Low gain anode followers usually work, but will oscillate if conditions are right.

I do have a nice scope, however, clipping one end of the shielding doesn't remove the shielding in this case, it removed the ground loop the shielding connected at both ends was causing. The shielding still has a path and continuity to ground.

Also, the microphone wasn't louder prior to clipping one end of the shielding, so that's not likely the cause.

Well, I reversed the transformer wires from the transformer PCB, and apparently something is marked backwards. I dunno, but it's much louder now. Still not as loud as my EF47 though, but much more reasonable.

UPDATE:

Here are my new voltages:
H: 5.85V
B+: 116.8V
A: 54.5V
K: 1.6V
Voltage across R10: 62V

It sounds good there, but I still have to crank the input gain much higher than the EF47 (both on cardioid). 
« Last Edit: March 25, 2021, 06:22:01 PM by JMPGuitars »


 

Related Topics

  Subject / Started by Replies Last post
374 Replies
104880 Views
Last post March 07, 2021, 03:49:47 PM
by Purplenoise
10 Replies
3060 Views
Last post June 01, 2018, 06:15:23 PM
by hop.sing
12 Replies
1851 Views
Last post March 07, 2019, 07:08:13 AM
by alhe
5 Replies
397 Views
Last post March 07, 2021, 12:10:33 AM
by athnony