[ln76d]

I didn't investigated the feedback issues, because never had any problem with it.
Hard to say - maybe the reason is elswhere than mentioned in the other thread.
Also i don't know what sit inside the silicon replacement - so hard even to compare.

[4earstudios]

Hello, great insight , a read through the forum and have two questions just to clarify : the construction we see here ist the C version? and 2. i do have a ac701 tube and want to built it with that - all i need ist to set the right voltage in the PSU ? beside that everything has to be built like in the instructions or am i missing smthg... thanks Daniel

[4earstudios]

Hello me again, wondering about the floating scheme, building version c, do i have to make connection from point to point as seen on the floating diagram...or is it made with the connection of the components as seen in the pictures of the built...thx Daniel

[ln76d]

Danny  boards will let you build both B and C version.
4V for AC701 heater.
Don't understand your next questions.

[4earstudios]

Thx for your answer on the second picture on site 1 : Floating Scheme connection For C version - there are white lines between some solder points - do i have to connect them? sorry for being so noobish - i usually build gear with step by step instructions...

[thekim1]

Hi,
I got a problem with my m49c build.
After putting everything together i got the mic working for about an hour, then there was a loud noise in the audio input on the soundcard as the fuse broke on the m49 psu. After changing the fuse i cant get the mic to pick up audio.
Took a look inside both the psu and mic but could not se anything that had broke, the 5840 tube is still glowing when the psu is turned on.

This is the readings i got inside the mic with the pattern set to cardioid:
K: 3.74v
A: 6.35v
H+: 5.98v
FGRID: 4.18v
4: 5.95v
5: 119v
6: 55.2v
R8-R9: 40.0v


EDIT:
Found the problem, broken tube. Now everything is showing the right voltages and the mic sounds fantastic!

[kpearsall]

Is anyone else using a 6.3v pilot lamp? How are you wiring it? Seems obvious to run it off the heater if the PSU will handle it. However, if the mic cable isn't properly connected, unloaded you'll send maybe 24v to the bulb. It's a number 47 1 watt bulb, so should I just throw a 1 watt 625 ohm or so resistor in series or just buy extra bulbs in case I do something stupid. Is there a best practice that anyone uses to do this in a better way?

Thanks!

[captainate]

Thx for your answer on the second picture on site 1 : Floating Scheme connection For C version - there are white lines between some solder points - do i have to connect them? sorry for being so noobish - i usually build gear with step by step instructions...

Hopefully you've figured this out by now, but the answer is no... there are traces under the PCB that would connect these points if you were not using the floating scheme, but since you are connecting them directly to the turret pin it is unnecessary to do anything else.

[captainate]

At the risk of opening a can of worms, are there any justifiable reasons to use a tantalum cap over an electrolytic cap in C9? It is very difficult to research the subject as people seem to have emotional reactions regarding audio capacitors.  Since one is risking a dead short if the cap fails, what supposed benefits does one receive in return?

[Colorblind]

Does anyone have any experience in modding the TPS100 style PSU for this microphone? What are the necessary mods?

Thanks!

I would also like to know this.   I built Dany & Oliver's D-EF47, and I found the PSU wiring diagrams a bit more newb-friendly than what's available for the D49. 

[TillM]

I need your help please.
This is my third M49 build but with this one, I don't know what I've doing wrong.
As soon when I connect the tube cable from the PSU to my microphone i have a bridge with the shield and the heater voltage. When I test it with my DMM continuity tester every from Binder to PSU pcb, and from tube cable to tube cable, everything is okay, but when I put the cable on the mic, the continuity tester beeps when i check pin 3 and 4 . I can’t see on the schematic that this should be.
On my PSU I use a 25k trimmer for the capsule voltage. I can’t get lower than 123v.
With my first build, i could also turn it down to 110v.
I don’t know what’s going on, it’s a bit frustrating, cause I build everything the same like the older ones.
When I first fire up my PSU with the mic I burn down my tube.
I hope someone can help me.

[ln76d]

If pin4 is heater and pin3 is ground then continuity is normal thing.
Are you using in each build the same power transformer?

[TillM]

If pin4 is heater and pin3 is ground then continuity is normal thing.
Are you using in each build the same power transformer?

Yes everything is the same.
I realized that I come with my soldering iron on the 5k trimmer.
I will change it first and then I also check the values from my 25k trimmer on the PSU.

Thanks for your help.

[TillM]

Now install a new trimmer and make a first test without tube.
When i put a 47ohm resistor between pin 4 and 7 i can bias the heater voltage to 6,3v.
Also changed the 25k trimmer. Still the lowest point for B+ is 123v. I can't go lower.
Well, when I now connect the Mic to the PSU I get following voltages. (As I said, I test it without tube, don't know whether it can work).
Now I get between HG and...
K=0v
A=27,26v
H+= -63,1v (why minus?)
Fgrid=0v
On r9 I get 27,71v and on r11 -27,49v ().
I check my wiring, it seams everything alright as far as I can see and check with my continuity tester.
I don't think that the tube inside will change something.
I'm a bit confused now.
appreciate every help

[rmburrow]

Recheck your wiring and look for errors such as solder bridges, etc.  Then install a tube in the mic  to load down the power supply... the HT will change with a load connected and the variable HT adjustment should work...check the heater voltage since that may change with the load...

Alternatively, check your wiring and then temporarily connect a 120 k 1 w resistor across the plate terminal to ground, and a 21 ohm 1 w resistor across the heater terminals without a tube installed.  Check if the variable HT adjustment works, and look for 6.3 volts at the heater pins...  Cheaper to burn up a couple resistors in case of a problem than a tube...

[rmburrow]

BTW who is building M49 metalwork that is closest to dimensionally correct and finish-correct to the original M49 these days?

[TillM]

Recheck your wiring and look for errors such as solder bridges, etc.  Then install a tube in the mic  to load down the power supply... the HT will change with a load connected and the variable HT adjustment should work...check the heater voltage since that may change with the load...

Alternatively, check your wiring and then temporarily connect a 120 k 1 w resistor across the plate terminal to ground, and a 21 ohm 1 w resistor across the heater terminals without a tube installed.  Check if the variable HT adjustment works, and look for 6.3 volts at the heater pins...  Cheaper to burn up a couple resistors in case of a problem than a tube...

Thanks for your advice. But I’m still confused. Why my PSU B+ can even with load just adjust to minimum 123v.

[rmburrow]

If the HT adjustment is simply a trim pot in series with the supply going to the mic, a load is necessary to set the HT.  If the trim pot adjusts a voltage regulator of some sort, then the output voltage should be able to be set without the load.  I'd have to see a schematic to know what is there...

Play it safe and use the resistors to load the supply for testing until you are certain the supply is working as intended.  Burning up a couple of resistors is less expensive than destroying a tube....especially if the tube is an AC701 or other high value device...

[TillM]

If the HT adjustment is simply a trim pot in series with the supply going to the mic, a load is necessary to set the HT.  If the trim pot adjusts a voltage regulator of some sort, then the output voltage should be able to be set without the load.  I'd have to see a schematic to know what is there...

Play it safe and use the resistors to load the supply for testing until you are certain the supply is working as intended.  Burning up a couple of resistors is less expensive than destroying a tube....especially if the tube is an AC701 or other high value device...

I test it with tube, the good thing is, the tube burn not down, otherwise they even start to burn.
Voltages are following.
K=0v
A=86v
H+=0v

I build Danys version C. Necessary for K are R9 with 1Mohm, the trimpod (5k) and C9.
The PSU is passive. I build Danys which comes with the M49 pcbs.
The heater voltage on the PSU even loaded with the tube shows 22v.
When i put a 47ohm resistor between pin 4 and 7, then I can adjust the pot to, lets say 5v.
When I load the PSU with the Mic and tube then H+ shows 20v.
I use Mobys BV11 transformer.
appreciate every help.

[TillM]

Today I had the chance to test the mic and psu with my old working mic, that I sell my friend.
The PSU works as it should.
The mistake is definitely in the mic.
I checked with my continuity tester that all cables have the right position.
The mistake must be in the mic circuit.
I get 0v at K, 87v at A and at H+ 0v.
The PSU react like it’s not loaded.
Could it be possibility that the 150mohm resistor is broken, while I solder it ?

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