DIY load bank

People

This is a very short example. Building a load for a power supply should be a meta or sticky better written than this.

I often power up a just built or worked on power supply on a simple resistive load bank. This can save the circuit that you just built from overvoltage

You need to know how to use ohms law and DC power.

Lets say a G7 go to the spec sheets and find the fil current and voltage
Use Voltage 6.3 VDC and current .2 amps to start

a resistor to sub for the heater would be 6.3/.2 for 31.5 ohms use a 33ohm it is close enought.
Next you know the current and voltage so voltage X current = DC power
6.3VDC X .2amps =1.26watts

33 ohms at 2 watts
or three 100 ohm in parallel at .5watts for 33.3 ohms at 1.5watts.

Now if you underheat the voltage and current will be a little different but this should be close for a load test of the power supply

Simple stuff

Then do the B+. One way, Look at the cathode voltage divide the cathode resistor voltage by the resistor value this should be very close to the plate current. Or you could use the voltage drop across the plate R

Then calculate the capsule voltage divider and pattern resistors total value and then that value current at the rated B+

Add up the currents and calculate the needed resistor value and wattage.


Ripple you will need a scope for.

HELLO

I am trying to help out.

Power supply problems? test the supply itself under load.

This is usefull info, is is almost paint by numbers, but one has to do simple math.

yeah ... it's cool

people may just be taking it all in
and
digging through their wire wound resistors to find some that will add up right.

Yep, just taking it in here Gus. :thumb:

Thanks alot! I understand this now, i think..It all makes better sense anyhow.

But, if you could further explain this to me perhaps?
"Then calculate the capsule voltage divider and pattern resistors total value and then that value current at the rated B+
Add up the currents and calculate the needed resistor value and wattage."

What is the capsule voltage divider?

Im guessing the pattern resistors set the voltages for the front and backside of the capsule, which in term set the polar pattern, right?

But other than that im not shure how to proceed with this.
Sorry if this is very basic and i dont understand much, but atleast im trying to. Is there any book i should read about this stuff btw?

/J

alk509 has nice pics on his page that show testing his homemade tube mic power supply with a dummy load:

http://home.comcast.net/~alkoury/ak78.html

This might help anybody wondering how to implement what Gus is describing.

thanks!
/J