I am working on different mics, and I have to similiar PSU's that both, (for U67 builds), get very hot on the R2/R3 resistors. I use Triad VPT230-110 (in the Mouser Bom list) transformers on both, the have 265volts on the secondary. I have tried different values on the resistors, but still very hot. Any suggestions?
Another PSU question
- Thread starter Greenie
- Start date
Help Support GroupDIY Audio Forum:
rock soderstrom
Tour de France
My suggestions again:
Greenie, 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...
And noone here can guess where R2/R3 are connected in the circuit, what they're supposed to do, what they're supposed to be rated for, etc.
if you get 375V across capacitors rated 350, it's not meant to be run without the proper microphone attached
rock soderstrom
Tour de France
Are you still having fun? Zero information, your questions are not answered, the guy is completely resistant to advice. People, don't let this guy troll you...
I am sorry you feel that way.
Ok, so the voltage is dependant on the mic drawing the voltage. Good advise, thank you.
Ohm's Law...
Thanks, I get it.
With microphone attached I get 333v at R2. (Sorry not ignoring, I am battling with two u67 builds that I don't understand at all at the moment.)Good to know only SOME of my posts get ignored
Which "R2" are we talking about??? In the schematic you posted in #7 here, R2 is a 22 ohm on the heater line. Unless i'm completely blind or something...
It would really help us (the people who are trying to help you out of... perhaps misguided kindness) if you actually knew WHAT you're asking help about
Or maintained some sort of consistency...
MagnetoSound
Well-known member
Current!
I homestley trying to figure out how a PSU is working, so I might misunderstand the advice I get, I have two u67's and I am in a bit of the deep darkness here,Which "R2" are we talking about??? In the schematic you posted in #7 here, R2 is a 22 ohm on the heater line. Unless i'm completely blind or something...
It would really help us (the people who are trying to help you out of... perhaps misguided kindness) if you actually knew WHAT you're asking help about
That question had an attached schematic picture which showed R2 as a 6k8 on the plate supply. The schematic is labeled "1st Gen NU67."
Resistors convert power to heat, so the temperature of a resistor is directly related to the power dissipated by that resistor. Power dissipation is related to voltage by Ohm's Law as Khron continues to point out. Voltage across the resistor, not voltage at one end of the resistor measured against the reference/ground connection.
Power dissipation capability of a resistor is essentially limited by materials and size. Higher power resistors typically need to be larger so that the total heat is spread through a larger volume of material (and dissipated out through a larger surface area). Good datasheets should include thermal specifications that describe the thermal resistance of the package which lets you calculate the temperature rise above ambient air temperature of the device at a given power dissipation.
So to come back around to your starting question if I were to try to answer this from an engineering standpoint, I would say:
- measure the voltage across the resistor
- from the first step, calculate the power dissipated
- measure the air temperature
- measure the resistor temperature
