Le Roux

Haha!

Thanks for pointing out my dumb error  :-[
Back plate and rear capsule reverse. WOW  :o

Dead quiet and sounds amazing!

Thanks for your help and Danny for the project!

Cheers
Neil


Haha!

Thanks for pointing out my dumb error  :-[
Back plate and rear capsule reverse. WOW  :o

Dead quiet and sounds amazing!

Thanks for your help and Danny for the project!

Cheers
Neil

Glad it worked out ,
wich tube did you use and what bias scheme  and capsule ,
best,
Dan,

Le Roux

RCA 5840
Beesnees M7 capsule

B+ 116 V
H+ 6.09 V
Plate Voltage 41.5 V
0.745 mA

Is that too high for current?
If I raise the B+ to 120V, it increases the current to close to 0.8mA
Like it sounds amazing the way it is

Cheers
Neil
« Last Edit: April 14, 2020, 11:06:23 AM by Le Roux »

Delta Sigma

Did you build the M49 'b' or 'c'?

What transformer?
Neil Fitzpatrick

Le Roux

ioaudio transformer BV11 off the top of my head
M49 "B" Version

Sorr

Are those M49B bodies still available?

TillM

Are those M49B bodies still available?
There was no specific M49b body.
Which body do you mean?

cofrus

Hi ,
Yes I’m having the same issue with the
Studio 939 M49 mic body. As recommended  on Vintagemicrophones web page.

The holes don’t  come close to matching the PCB, because the barrel has a diameter of 65mm and the Vintagemics PCB is 60mm.
Also the total depth between the base of the barrel and the grill mounting is only 38mm whilst the vintagemics design requires a minimum of 40mm.
Stumped.


TillM

Hi ,
Yes I’m having the same issue with the
Studio 939 M49 mic body. As recommended  on Vintagemicrophones web page.

The holes don’t  come close to matching the PCB, because the barrel has a diameter of 65mm and the Vintagemics PCB is 60mm.
Also the total depth between the base of the barrel and the grill mounting is only 38mm whilst the vintagemics design requires a minimum of 40mm.
Stumped.

You have to modified it.
But that’s not the big problem.
Just buy a round acrylic plate with 3mm thickness and drill it for your needs.

Winetree

I'm using an AMI BV11r with wired leads.
From the attached diagram with leads are ABCD
wired into the round puck.

« Last Edit: June 09, 2020, 07:56:03 PM by Winetree »


Ralf

You have to modified it.
But that’s not the big problem.
Just buy a round acrylic plate with 3mm thickness and drill it for your needs.

Ouch, I didn't know that. So the PCBs only match the TLM49 body? I just recently ordered the chunger CU-49 body and the D49 PCBs. The custom acrylic board would be for the capsule mount I suppose?  On the main board I can just drill new holes to make it match? Well, if I have to do that I might as well just go all acrylic and build me a nice looking custom turret board and not bother with the D49 PCBs at all.

Ralf

I need to modify the PSU to work for the original AC701 tube, so I need around 4V for the heater. If I build as in the schematic I am reading a range roughly between 20V and 25V. Can somebody point me to what would be the best way to modify the PSU to get the range for the heater voltage right? Seeing that R4 forms a voltage divider together with the trimpot I was thinking about lowering R4, but it is already pretty low (680Ohm) and I would have to use a value around 100Ohm. I’m a bit worried that the circuit would draw too much current if I do that. Thanks for any suggestions.

Ralf

Answering myself: Further up in the thread it was reported that the unloaded heater voltage of the PSU can indeed be in the neighbourhood of 22V, but with a tube connected it will drop to around 6V. This seems like too much of a gamble for me for a 600€ tube.

I am thinking about crocodile-clipping lower values into R4, then slowly working my way up once I have the tube connected just to make sure I am not hitting it with more than 4V. Does anyone have any experience with good R4 values for an AC701 tube?


Moby

Answering myself: Further up in the thread it was reported that the unloaded heater voltage of the PSU can indeed be in the neighbourhood of 22V, but with a tube connected it will drop to around 6V. This seems like too much of a gamble for me for a 600€ tube.

I am thinking about crocodile-clipping lower values into R4, then slowly working my way up once I have the tube connected just to make sure I am not hitting it with more than 4V. Does anyone have any experience with good R4 values for an AC701 tube?
Ohms law is your partner here. You have to check the datasheet about the tube heater current and to calculate the dropping resistor. That's all. Calculate it 3 times before you proceed. ;)
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

Ralf

Ha! Now it all makes sense, thanks. According to the AC701 datasheet and Ohms Law the heater will present a load of 40 Ohm. This means the voltage will drop to around where it should be when that load is in parallel with R4. According to my calculations it wouldn’t hurt to go down to 330 Ohm with R4 in order to get more usable range on the heater trimmer pot and to make the “death zone” for the tube a bit smaller on the pot.

Moby

Ha! Now it all makes sense, thanks. According to the AC701 datasheet and Ohms Law the heater will present a load of 40 Ohm. This means the voltage will drop to around where it should be when that load is in parallel with R4. According to my calculations it wouldn’t hurt to go down to 330 Ohm with R4 in order to get more usable range on the heater trimmer pot and to make the “death zone” for the tube a bit smaller on the pot.
you should also calculate the wattage for the resistor. 20v drop it's gonna burn it in the heat. Don't be shy with wattage, you don't want to overheat it.
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

I'm having the same issue as JMPGuitars, low output and a bit of noise. Mic sounds good but it's definitely quieter and noisier than it should be. At the risk of speaking for a stranger, it appears we have the same build - 5840w tube, C version, T49 transformer.

I know Dan built his original C version with the T49, but I noticed AMI doesn't reference the 5840 in their T49 information, but does for the BV11r. The specs between these two trafos are quite different, and on paper it does seem this could be the culprit. Would love for Dan especially to weigh in on this, but all ideas welcome!
~Nathan

TillM

Check your transformer with a DMM.
Maybe primary and secondary is changed.
I would give it a try.
The C-version don’t tend to noisiness, also the output is good.

Nele

Hi everyone,

I'm finally getting around to finishing the build of the M49B with the 6s6b-v tube. I have a few issues:

- the mic is working correctly, patternswitch is working but the output signal is really low. I'm using the BV11 by advancedaudio but it is really tiny compared to the other BV11 versions I see in the pictures. Is this really a BV11?
- I can't get the heater voltage up to 6.3V. The maximum is 5.9V. I'm using the psu that came with the other pcb's from  vintagemicrophonepcbkit.
- I accidentally connected the mic without setting the heater voltage first so the first few minutes the tube got the full B+ but very low heater voltage. Can this have damaged the tube?


Moby

Hi everyone,

I'm finally getting around to finishing the build of the M49B with the 6s6b-v tube. I have a few issues:

- the mic is working correctly, patternswitch is working but the output signal is really low. I'm using the BV11 by advancedaudio but it is really tiny compared to the other BV11 versions I see in the pictures. Is this really a BV11?
- I can't get the heater voltage up to 6.3V. The maximum is 5.9V. I'm using the psu that came with the other pcb's from  vintagemicrophonepcbkit.
- I accidentally connected the mic without setting the heater voltage first so the first few minutes the tube got the full B+ but very low heater voltage. Can this have damaged the tube?
The transformer you used and gave a link here is not Bv.11 but some T14-1 modern variation. Bv.11 use the same sized lamination core as the Bv.08, so called UI30/25 and it's much larger than T14-1. Of course, It does not matters regarding signal level (it affects headroom),  ratio is the important. But, with UI30/25 you are in the "safe zone". Ratio should be 7:1 or 10:1 depending on the M49 revision.
Yes, it's possible to damage the tube withouth proper filament, but generally, tubes are flexible devices. So, you should always provide filament first, then anode voltage to keep tube safe.
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com


 

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