Hi. I have a D-47 build that sounds fanatastic, with the flat 47 capsule and a Funkenwerk transformer. My problem is that I get a to high voltage coming out of the PSU, the lowest I get is 120v. Any advice on how to get it down to about 10v?
To high voltage D47 mic
- Thread starter Greenie
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rock soderstrom
Tour de France
Adjust the zener diodes and the resitors.
RuudNL
Well-known member
If you get 120 V at the point where you should have 10 V, there must be something seriously wrong!
Usually a power supply for a tube microphone produces 6,3 V for the filament and 120 V (or higher) for the anode voltage. An exception is the 'classic' U47 with a VF14 tube, that uses 105 V for both the anode voltage and the filament voltage.
Edit: Aah, I see he wants to lose 10 volts! (It was probably too early in the morning when I read it before...
)
Usually a power supply for a tube microphone produces 6,3 V for the filament and 120 V (or higher) for the anode voltage. An exception is the 'classic' U47 with a VF14 tube, that uses 105 V for both the anode voltage and the filament voltage.
Edit: Aah, I see he wants to lose 10 volts! (It was probably too early in the morning when I read it before...
)
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rock soderstrom
Tour de France
ohms law is your friend.
rock soderstrom
Tour de France
he actually wants to reduce B+ by 10V...
Greenie, you should approach the whole thing in a more structured way, it doesn't make sense to open several threads on the same topic.
Why don't you approach it like this?
Find a circuit diagram and check whether it really matches what you have in front of you!
If necessary, correct the schematic and then post it here with your question. Add some nice photos of your unit.
Then learn Ohm's law and adjust the corresponding resistor.
If you have problems with this, I'm happy to help, but put some structure into your questions so that we know what we're really talking about. Otherwise it's no fun...
MagnetoSound
Well-known member
Increasing [R3] with the load connected is the best way to dial in the B+. Use a 22k or 47k pot, adjust until you get what you want, then measure the required resistance. Find a fixed resistor that’s close and install that. This marginally improves the filtering too.
But, as Rock says, you need to learn about Ohm’s Law. Pulling current through a resistance causes voltage drop. It’s easy to calculate once you do it a few times. Just don’t forget to add the point and zeros because it’s milliamps, not amps.
But, as Rock says, you need to learn about Ohm’s Law. Pulling current through a resistance causes voltage drop. It’s easy to calculate once you do it a few times. Just don’t forget to add the point and zeros because it’s milliamps, not amps.
RuudNL
Well-known member
Aah, I see. Well, a resistor is the solution. It depends on the current, usually not more than 1 mA.
I would start with 10 K or 15K and see what the voltage is you get then.
And measure the voltage under load.
By the way: it is not important the get the exact voltage, 1 volt more or less doesn't really matter.
It's a tube, not a computer...
I would start with 10 K or 15K and see what the voltage is you get then.
And measure the voltage under load.
By the way: it is not important the get the exact voltage, 1 volt more or less doesn't really matter.
It's a tube, not a computer...
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MagnetoSound
Well-known member
(and kilohms, not ohms)
Hi Ruud. I put in a 2k7 resistor and now I am able to dial in 105v. A million thanks.
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Thanks for great advice, I am now able to dial in the righ volt.
Cqwet Dbdfte
Well-known member
- Joined
- Oct 2, 2023
- Messages
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More volts on that tube would most likely make it more linear. That extra extra ~8% power dissipated in the plate load resistor from the increased voltage does not hurt.
Capacitors, and other dielectrics will laugh at the difference.
However, if this voltage had somehow changed the cause should be determined.
Capacitors, and other dielectrics will laugh at the difference.
However, if this voltage had somehow changed the cause should be determined.
When the voltage was 120v the mic had considerable noise, that vanished when the voltage was lowered.
It generally known that tubes used in very high z input circuits can live longer and work quieter with lower plate voltages , you might loose a little headroom with lower plate volts , but your reducing noise at the same time so its not so much of a problem ,
Hey Greenie, what exactly did you do? Did you replace the resistor at r3 with at 2k7 or did you do something else. My psu seems to have too high a charge as well.
Thanks,
Z
In my case I just put in a 5w 2k7 resistor, peoblem was that the origina<l valu got really warm, and eventually burnt.
