Neumann U67 Clone : D-U67 Tube Microphone Build Thread.

[C12VR]

Anyone has any source for the 400M (1/2W) resistors?

Mouser and Farnell don't seem to stock any

Thanks

you could probably tie a few lower value resistors together (series) if necessary, space permitting. I have done this for the high-value resistors in a C12 clone.

 

[doqmemory]

Anyone has any source for the 400M (1/2W) resistors?

I used 1/3 watt MOX-400224006JE from DigiKey (marketplace order from Ohmite), but they are out of them now. I also ordered 500M 1/2W HVA05FA500M, which should also work fine, but have not yet tried them. They do not really need to be 1/2 W, as mentioned elsewhere. I suspect 300M would be fine, too.

If anyone wants to get a group by group buy together, we could order the last 27 of the Ohmite 400M OHM 2% 1W AXIAL, since they are not being made any more.

Since 1/4 W should be fine, MOX200004006JE should also work.

 

[doqmemory]

you could probably tie a few lower value resistors together (series) if necessary, space permitting.

Space is the problem with the D-U67 (and M269b/c), since the hi-Z bridge is rather full already.

 

[TLRT]

MOX200004006JE is fine, even 1/10W should be enough, capsules doesnt have any significant current consumption.

 

[Whoops]

If anyone wants to get a group by together, we could order the last 27 of the Ohmite 400M OHM 2% 1W AXIAL, since they are not being made any more.

Since 1/4 W should be fine, MOX200004006JE should also work.

Thanks for the offer mate, but no need for a group buy at least for myself as the 1/4w from Mouser is fine and it's readily available.
So I will place an order in Mouser.

Thanks also to TLRT for the explanation

here is the link:

https://pt.mouser.com/ProductDetail/Ohmite/MOX200004006JE?qs=LlUlMxKIyB06u5IfN9aihg==

 

[gevermil]

Trying to search this thread but no luck so far on trying to lower my H+ .
For a while adjusting my power supply has been frustrating .
With my pot maxed out I can only get to -6.4 . Any Ideas what resistor value to replace or add in series with the pot ?

 

[Whoops]

Trying to search this thread but no luck so far on trying to lower my H+ .
For a while adjusting my power supply has been frustrating .
With my pot maxed out I can only get to -6.4 . Any Ideas what resistor value to replace or add in series with the pot ?

Post a schematic of your PSU circuit with the respective AC voltages and DC voltages in each component of the Heaters supply.
With that info I guess it will be easy to help you out

 

[gevermil]

sorry , meant to say H- .
Thanks WHoops
The schematic is the same as page one in this thread . Ill post some measurements

 

[Whoops]

Any difference when building an U67 circuit in using 470M resistors instead of 400M resistors?
Does it make a difference operation wise or is it irrelevant?

Thanks

 

[Greenie]

What voltage would be enough on the 10n capacitors on the U67 board, I have some 200vs ones?

 

[mrbutterskin]

200V should be fine. The highest voltage I see across the 10n caps is 120V (C1 and C8). The rest are lower than that.

 

[Greenie]

200V should be fine. The highest voltage I see across the 10n caps is 120V (C1 and C8). The rest are lower than that.

Thanks...

 

[ROC127]

Hello,

I recently started this u67 build and the heater and plate voltages check out on the PSU and mic with and without a tube installed. However I only get a loud hum when testing the mic with a pre. Can anyone post other voltage values I can check to try and narrow down the fault? I also have an o scope if anyone knows good points to test the signal path. I’m using an AMI BV12, Neumann k67 and generic 12AX7 sovtek tube. Thanks for any help.

 

[Purplenoise]

Hello,

I recently started this u67 build and the heater and plate voltages check out on the PSU and mic with and without a tube installed. However I only get a loud hum when testing the mic with a pre. Can anyone post other voltage values I can check to try and narrow down the fault? I also have an o scope if anyone knows good points to test the signal path. I’m using an AMI BV12, Neumann k67 and generic 12AX7 sovtek tube. Thanks for any help.

12ax7? Did you adopt the circuit for 12ax7? Why don’t you use ef86 that the circuit is designed for?

 

[ROC127]

12ax7? Did you adopt the circuit for 12ax7? Why don’t you use ef86 that the circuit is designed for?

Ah, I believe I may have a gap in understanding. I put a cheap 12ax7 just to test Expecting it to function well enough to verify function and I’d purchase an ef86 later. My understanding was that ef86’s and 12ax7’s were interchangeable. Sounds like that’s not the case.

 

[FarisElek]

Look at the datasheets for those tubes. They're not even similar.

 

[Purplenoise]

Ah, I believe I may have a gap in understanding. I put a cheap 12ax7 just to test Expecting it to function well enough to verify function and I’d purchase an ef86 later. My understanding was that ef86’s and 12ax7’s were interchangeable. Sounds like that’s not the case.

Not interchangeable..very different tubes. You need an ef86

 

[Whoops]

In the PSU Mouser BOM, the B+ potentiometer chosen is rated at 5W (25K) and the one for the Heater supply is rated at 3W (100R).

Do the Potentiometers for the PSU really need to have such an higher wattage rating?
Couldn't at least the one in the B+ have a much lower rating than 5W?

Thanks

 

[dmp]

Do the Potentiometers for the PSU really need to have such an higher wattage rating?

B+ current ~3mA, heater current 200mA
power dissipation is I^2*R
So the B+ pot is dissipating 0.225 W
Safe to have lower wattage on the B+ pot (1 W would be fine with a decent safety factor).

In the schematic the heater pot resistance is 50 ohm (maybe I have a old schematic?)
Then the heater pot is dissipating 2 W
With 100R, the pot is dissipating 4W, I would not suggest a 3W 100R pot as this will be overpowered at high R

 

[Whoops]

B+ current ~3mA, heater current 200mA
power dissipation is I^2*R
So the B+ pot is dissipating 0.225 W
Safe to have lower wattage on the B+ pot (1 W would be fine with a decent safety factor).

Thank you so much for the explanation.
1W and higher Pots are harder to find, I guess 0.5W is still fine and also with a safety margin. 0.5W rated pots are much easier to get as those are pretty comman

In the schematic the heater pot resistance is 50 ohm (maybe I have a old schematic?)

In this project (D-U67) schematic and also in Neumann's schematic the heater pot is stated as 50R, but if you check the Mouser BOM in the first post of this thread it will show a 100R Pot instead.


https://pt.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=b5c122b4d0

Then the heater pot is dissipating 2 W
With 100R, the pot is dissipating 4W, I would not suggest a 3W 100R pot as this will be overpowered at high R

I just noticed now that Neumann's schematic state the Heater pot (50R) with a rating of 1W, maybe a mistake?
here it is: