I am starting to collect the things required to work on tube amplifiers. I've read some interesting things about isolation (?) transformers .
Any suggestions for safely using one? I became aware of them after reading your safety sticky.
Is an Ultra Isolator from Topaz what I'm looking for?
Regards,
Steve
Any suggestions for safely using one? I became aware of them after reading your safety sticky.
Is an Ultra Isolator from Topaz what I'm looking for?
Regards,
Steve
Instead think about installing a small isolation transformer into any transformerless amp you work on - then it will be safe AFTER it leaves your bench... they're about $15 - a small price for safety...
You don't need an isolation transfomrer for amps that have a power transformer - though I use my capacitor tester to check for line-chassis isolation (insulation resistance function) before I plug in any unknown piece of equipment. I often find a leaky line-chassis capacitor - there's a reason they're called the "death cap".
You don't need an isolation transfomrer for amps that have a power transformer - though I use my capacitor tester to check for line-chassis isolation (insulation resistance function) before I plug in any unknown piece of equipment. I often find a leaky line-chassis capacitor - there's a reason they're called the "death cap".
What you need is any sort of power transformer (which is generally the case) AND the ground wire from the mains (green) FIRMLY tied to the chassis.
You might consider using a variac; it provides no isolation (that's the job of your power transformer) but allows you to slowly ramp up the voltages and catch mistakes before they become explosions.
You might consider using a variac; it provides no isolation (that's the job of your power transformer) but allows you to slowly ramp up the voltages and catch mistakes before they become explosions.
A variac is plugged into the transformer now. It (variac) is old and has no earth ground. I will remedy this with a proper power cord and receptacle.
Thank you for the clarification.
I asked about Transformer Isolation on another site and was basically laughed at. I take safety seriously.
Thanks everyone for taking the time to answer. You may have saved a life.
Steve
One additional step may be worth your consideration, following SY's good advice. It's a good idea to be certain that your AC wall outlets are wired correctly. The green ground wire will be ineffective unless it's actually connected to ground. For $5 or less there are small "plug in" wiring testers, available at electrical supply houses and hardware stores. They are usually yellow and have three small indicator lights on the body, which will display wiring faults. I've used one for over 25 years, and have found serious errors in places that I would not expect them!
Thanks for the tips.
I have a Furman product that lets me know the condition of the AC input.
It covers : open ground, open hot, open neutral, hot ground reversed and hot neutral reversed. Everything is plugged into a GFI.
Will you tell me the best way to shunt a cap to discharge the stored energy? I still get (low) voltage readings 16hrs later. I'm not sure what value resister to use.
Regards,
Steve
I have a Furman product that lets me know the condition of the AC input.
It covers : open ground, open hot, open neutral, hot ground reversed and hot neutral reversed. Everything is plugged into a GFI.
Will you tell me the best way to shunt a cap to discharge the stored energy? I still get (low) voltage readings 16hrs later. I'm not sure what value resister to use.
Regards,
Steve
Assuming it's a high voltage power supply cap, use a 220K 2W R with a couple of insulated clip leads. Other R's around the above value and wattage will also work fine.
Perhaps the safety and isolation thing is misunderstood. Here is a chunk. GFCI’s do not need the green wire to operate. The green wire is not part of the function of the GFCI. They operate by sensing current in both the black wire and white wire. If there is a difference, just a tiny difference, they trip. Capacitors and chokes do not know GFCI’s. Turn on a serious power supply on your bench there will be a difference in current between the hot black wire and grounded white wire, the GFCI will trip. Your bench is not a good place for a GFCI if you do not like nuance trips.
Power supply transformers have much higher impedance than the branch circuit in the wall and will result in a much lower current if there is a fault. Not so much smaller that your heart could tell the difference if you become part of the circuit.
DT
All just for fun!
Thank you, this kind of information keeps beginners from shorting caps with a screw driver.
I was going to use the transformer for my stereo setup until I realized how (104.5 fahrenheit) warm it got during operation.
I do have pretty good electrical distribution and isolation as it is.
Thanks for the updates
Steve
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I'm actually quite well aware of how a GFCI/GFI operate, but did not have the time to go into detail - perhaps I should have.
In the 12yrs or so I have used a GFCI on my bench it has never once nuisance tripped, but the 4 times I can recall it tripping were due to faults on the mains side of things - the first was a failed Y cap in a cd player with a 2 wire line cord, the second a failed transformer in a piece of test equipment with a 3 wire line cord, the third a Marantz 9 with a power switch with an internal short to the case and hence chassis, and finally a friend's incorrectly wired guitar amplifier. In all 4 instances I was delighted that it tripped. In three of those cases the faulty piece of equipment would have found ground through me or through test wiring that would not have safely sustained the fault currents involved. The GFCI clearly earned its keep in those instances - and reacted a lot quicker than the breaker in the panel would have.
Note that I have serious bench supplies, a scope, a computer based FFT system, and a lot of test equipment and not one of these items has ever caused the GFCI to trip.
IMHO It is very cheap insurance for several potential fault mechanisms, and prevents massive current flow through unexpected paths in the event of an error or component malfunction on the AC input side of the device under test.
In the 12yrs or so I have used a GFCI on my bench it has never once nuisance tripped, but the 4 times I can recall it tripping were due to faults on the mains side of things - the first was a failed Y cap in a cd player with a 2 wire line cord, the second a failed transformer in a piece of test equipment with a 3 wire line cord, the third a Marantz 9 with a power switch with an internal short to the case and hence chassis, and finally a friend's incorrectly wired guitar amplifier. In all 4 instances I was delighted that it tripped. In three of those cases the faulty piece of equipment would have found ground through me or through test wiring that would not have safely sustained the fault currents involved. The GFCI clearly earned its keep in those instances - and reacted a lot quicker than the breaker in the panel would have.
Note that I have serious bench supplies, a scope, a computer based FFT system, and a lot of test equipment and not one of these items has ever caused the GFCI to trip.
IMHO It is very cheap insurance for several potential fault mechanisms, and prevents massive current flow through unexpected paths in the event of an error or component malfunction on the AC input side of the device under test.
Hello kevinkr,
My mistake, I am surprised that the GFCI works for that use. I learn by watching and doing, reading. My last job was in a teaching hospital. The biomed tech guys would never dream of using a GFCI on their bench and would even scoff as I did at the recommendation. The biomed equipment had internal safety devices, they did not want any non-hospital grade things interfering on their bench. We also had a test bench with 3 phase 480 volt supplied. The operating rooms 23 plus of them had isolation transformers with monitored isolated grounds. Stray currents were not good inside a patient.
That primary side GFCI will not help on the secondary side of our power transformers.
DT
This art is not just for fun!
My mistake, I am surprised that the GFCI works for that use. I learn by watching and doing, reading. My last job was in a teaching hospital. The biomed tech guys would never dream of using a GFCI on their bench and would even scoff as I did at the recommendation. The biomed equipment had internal safety devices, they did not want any non-hospital grade things interfering on their bench. We also had a test bench with 3 phase 480 volt supplied. The operating rooms 23 plus of them had isolation transformers with monitored isolated grounds. Stray currents were not good inside a patient.
That primary side GFCI will not help on the secondary side of our power transformers.
DT
This art is not just for fun!
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