I'm trying to solve a power problem with the A-side of the unit (the B-side is working fine). I replaced the original full wave copper sulfide rectifier, which was inop, with a new full-wave rec. That got the power flowing again, but I was getting 2.4 volts DC instead of 1.5 volts (the voltage it's supposed to put out). I then replaced all three of the 1500 mfd (3 volt) caps that surround the chokes with 1500 mfd (25 volt) caps. Now it puts out 2.85 volts DC. Since the A side of the farm radio it came with only needs 1.5 volts DC, I'm positive this is too much and will accelerate tube burn-out. Does anyone have any suggestions on what else could be wrong, or what I can do to reduce the A-side output? Your advice is greatly appreciated!

Hi Jeff,
The 2.8volt A voltage you describe is the output of your Power Shifter without any load. With a load, this voltage will decrease. To test it, you need to apply a simulated load (via a resistor) across the A output. The size of this resistor depends on the current drawn by the tubes of your radio. For example, it might use a 1A7, 1N5, 1H5, and 1C5. Add up the current drawn: the first three tubes draw .05 amps each. The last tube draws .1 amp. Total 0.25 amps. Pick a resistor when drawing 0.25 amps drops 1 1/2 volts, via Ohm's law. 1.5/.25 = 6 ohms. Therefore use a 6 ohm resistor for a test load. Place this resistor across your A output, and measure the voltage drop across the resistor with your DMM. It should be close to the 1.5v (or preferably 1.4v) which you want. If it is still too high, then put a permanently-installed resistor in series with your new rectifier to reduce it to the proper level.

Poston

:I'm trying to solve a power problem with the A-side of the unit (the B-side is working fine). I replaced the original full wave copper sulfide rectifier, which was inop, with a new full-wave rec. That got the power flowing again, but I was getting 2.4 volts DC instead of 1.5 volts (the voltage it's supposed to put out). I then replaced all three of the 1500 mfd (3 volt) caps that surround the chokes with 1500 mfd (25 volt) caps. Now it puts out 2.85 volts DC. Since the A side of the farm radio it came with only needs 1.5 volts DC, I'm positive this is too much and will accelerate tube burn-out. Does anyone have any suggestions on what else could be wrong, or what I can do to reduce the A-side output? Your advice is greatly appreciated!

Poston,

I'll give it a try. Many thanks!

Jeff

:Hi Jeff,
:The 2.8volt A voltage you describe is the output of your Power Shifter without any load. With a load, this voltage will decrease. To test it, you need to apply a simulated load (via a resistor) across the A output. The size of this resistor depends on the current drawn by the tubes of your radio. For example, it might use a 1A7, 1N5, 1H5, and 1C5. Add up the current drawn: the first three tubes draw .05 amps each. The last tube draws .1 amp. Total 0.25 amps. Pick a resistor when drawing 0.25 amps drops 1 1/2 volts, via Ohm's law. 1.5/.25 = 6 ohms. Therefore use a 6 ohm resistor for a test load. Place this resistor across your A output, and measure the voltage drop across the resistor with your DMM. It should be close to the 1.5v (or preferably 1.4v) which you want. If it is still too high, then put a permanently-installed resistor in series with your new rectifier to reduce it to the proper level.
:
:Poston
:
:
::I'm trying to solve a power problem with the A-side of the unit (the B-side is working fine). I replaced the original full wave copper sulfide rectifier, which was inop, with a new full-wave rec. That got the power flowing again, but I was getting 2.4 volts DC instead of 1.5 volts (the voltage it's supposed to put out). I then replaced all three of the 1500 mfd (3 volt) caps that surround the chokes with 1500 mfd (25 volt) caps. Now it puts out 2.85 volts DC. Since the A side of the farm radio it came with only needs 1.5 volts DC, I'm positive this is too much and will accelerate tube burn-out. Does anyone have any suggestions on what else could be wrong, or what I can do to reduce the A-side output? Your advice is greatly appreciated!

Jeff,
Here is another tip: Unless you have a supply of low-valued resistors to experiment with, the easiest way to apply your simulated load is with a wire-wound potentiometer. (Radio Shack has a 0-25 ohm/3 watt wirewound pot at about $3) Simply measure the resistance of the potentiometer with your DMM, and adjust it until you have the right value. Then install it across the "A" output and measure the voltage drop across it, as I described earlier.

Poston

:Poston,
:
:I'll give it a try. Many thanks!
:
:Jeff
:
::Hi Jeff,
::The 2.8volt A voltage you describe is the output of your Power Shifter without any load. With a load, this voltage will decrease. To test it, you need to apply a simulated load (via a resistor) across the A output. The size of this resistor depends on the current drawn by the tubes of your radio. For example, it might use a 1A7, 1N5, 1H5, and 1C5. Add up the current drawn: the first three tubes draw .05 amps each. The last tube draws .1 amp. Total 0.25 amps. Pick a resistor when drawing 0.25 amps drops 1 1/2 volts, via Ohm's law. 1.5/.25 = 6 ohms. Therefore use a 6 ohm resistor for a test load. Place this resistor across your A output, and measure the voltage drop across the resistor with your DMM. It should be close to the 1.5v (or preferably 1.4v) which you want. If it is still too high, then put a permanently-installed resistor in series with your new rectifier to reduce it to the proper level.
::
::Poston
::
::
:::I'm trying to solve a power problem with the A-side of the unit (the B-side is working fine). I replaced the original full wave copper sulfide rectifier, which was inop, with a new full-wave rec. That got the power flowing again, but I was getting 2.4 volts DC instead of 1.5 volts (the voltage it's supposed to put out). I then replaced all three of the 1500 mfd (3 volt) caps that surround the chokes with 1500 mfd (25 volt) caps. Now it puts out 2.85 volts DC. Since the A side of the farm radio it came with only needs 1.5 volts DC, I'm positive this is too much and will accelerate tube burn-out. Does anyone have any suggestions on what else could be wrong, or what I can do to reduce the A-side output? Your advice is greatly appreciated!