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what does amp and volt on a power supply mean?
Old 16th November 2009
Gear interested

Thread Starter
what does amp and volt on a power supply mean?

I want to know why power adapters / supply have very high voltage and low ampere
I seen 30 VAC for 600amp and 12VAC for 4A

What does each number really mean?

Doesn't voltage indicate how much potential power could be in the wire and ampere indicates how much actual electrical current is flowing through the wire?

The reason I am asking is because I have a
Tube Works
Serial # 44674
Date 7/26/1995
Real Tube Direct
Class "A" Transformerless True balanced Tube Cathode Direct Output.
- it require power supply of 30VAC/600mA

I lost my original power cable, THERE IS NO REPLACEMENT, I SPENT 3 HOURS RESEARCHING INTO DIFFERENT PARTS ALREADY. The closest I can find is RadioShack, EnercellĀ® Switchable 18/24V/1A AC Power Adapter Model: 273-331, $26
EnercellĀ® Switchable 18/24V/1A AC Power Adapter -

I have no hope of building one myself after seeing how people actually build their own electronic components, especially in shortwave radio. Really right now I am just hoping to learn how electricity powers different devices.

can I use higher or lower ampere such as 30VAC/400mA or 30VAC/2A? Can I use higher or lower voltage such as 50VAC/1A or 24VAC and 1A?

If I use higher ampere or voltage would it burn out the wire? If I use lower ampere or voltage would the radio simply not turn on? If I use high voltage and regular ampere does it mean the radio will work for a while but the control board will burn out? If I use regular voltage and high ampere does it mean the internal circuit breaker / fuse will burn out but the rest of the radio would be protected?

What if I use 12 VDC and 1A? Would direct current fry the Real Tube Direct?

Most of the modern electronic device uses DC because it's a stable low voltage power supply right?

This is what I know so far, please let me know if my assumptions are correct In typical term, AC Power Adapter convert AC (power in the wall outlet) to DC (low level but steady). This is seen in cellphone charger and laptops.

VCT is voltage current transformer

There are 2 different type of transformers
VAC is Volts Alternating Current
VDC is Volts Direct Current

Electrical curriculum: What is Voltage?
Volts are always measured along the flux lines of electric field, therefore voltage is always measured between two charged objects. If I start at the negative end of my flashlight battery, I can call that end "zero volts", and so the other end must be positive 1.5 volts. However, if I start at the POSITIVE end instead, then the positive battery terminal is zero volts, and the other terminal is negative 1.5 volts. Or, if I start half way between the battery terminals, then one terminal is -.75 volts, and the other terminal is +.75 volts. OK, what is the REAL voltage of the positive battery terminal? Is it actually zero, or actually +1.5, or is it +.75 volts? Nobody can say. The terminal can have several voltages at the same time.

What is an Amp?
The ampere, amp for short, is the standard unit of electrical current. It is defined as the current required to produce a certain force between two parallel and infinitely long wires separated by one meter.

According to Ohm's law, one ampere of current is produced when one volt of potential difference exists across a conductor with one ohm of resistance. One ampere is also equal to the flow of one coulomb of electric charge per second.
Old 16th November 2009
Lives for gear
mexicola's Avatar

voltage must be the same.
amperage can go higher.
I typically like to have at least 2x more current capacity in the psu than the device actually needs. A higher amp psu can usually achieve better performance out of the device because it's not struggling.
The device will not pull more current if your psu has a higher current capacity. It's that the psu is more comfortable supplying less current than it is capable of, which means the power will be cleaner and more reliable.

Using a higher voltage can damage internal components that are rated for a specific max voltage, which is usually only a few volts over the supply voltage, as higher voltage rated components cost more.
Old 16th November 2009
Lives for gear
brianroth's Avatar

Watts are Watts.

Watts = Volts x Amps

Old 18th November 2009
Lives for gear

To run it, you need to get a power supply that supplies 30V AC at AT LEAST 600mA. Anything less and it won't work right, anything more and it will probably blow up. If you just get a power supply with those specs you should be happy.

What happens with gear is that if you use too low of a voltage, the gear usually will take less current (thanks to ohm's law - if you reduce the voltage, the current goes down), but it probably won't work right, either.

If you use too high a voltage, the current will (usually) go up, and something will get too hot and burn out. Also, all amplifying devices (tubes, transistors, IC's) have a maximum voltage rating and if you exceed this, it burns out.

Note that I said 'usually' up there. There is one common case where raising the voltage causes the current to go down, and lowering it causes the current to go up - it's called negative resistance - and that's when there is a switching power supply in the piece of gear.

So when matching power supplies, you have to match the voltage and exceed the current, but you don't want overkill, either. I have a transformer somewhere downstairs that delivers about 30V and about 200 amperes - a stick welder. But that would be overkill (and noisy) for your little amplifier.
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