Hi, would like to know if two bulbs are needed for a current limiter if both lines are live (115VAC - 115VAC). I noticed there is only one bulb connected in series with the live wire and none on the neutral side. Am in the process of making one to test my amps which have not been used for a year and a half. Our power lines are both live unlike in other countries. Thank you in advance for your advice/help on this matter.
Benzene
Benzene
Just one bulb. The AC circuit into a piece of equipment is just a series circuit and so it doesn't matter (electrically) where in that chain the bulb goes.
Thanks Mooly for your advice! May now proceed wih the bulb current limiter test on my tube amps. Have done earlier a visual (on the caps and resistors) and didn't notice any physical change since I last used them almost a year and a half ago. Just wanted to be sure before I start listening to some music in my system. Thanks again and stay safe always!
Benzene
Benzene
Just an alternate view.
I highly recommend a variac for testing tube or solid state equipment. With a bulb limiter your energy to the circuit is unknown and he characteristics of the limiter may interact with the circuit. Using a variac you always know (and I mean know for certain) how much voltage you are supplying the circuit. It also allows you to run the circuit at reduced voltage so you can safely troubleshoot it.
I've serviced equipment for over 45 years now. The first thing I bought past my meter, 'scope and generator was a variac. Soldering iron came first, and hand tools. Since then I have bought larger variacs and made sure they were fully "metered" with output voltage and current meters. My current one has switchable meter functions, which I am not crazy about but it works. This one does measure leakage current easily. It's a B&K 1655 AC Power Supply. Got it cheap on Ebay so I couldn't resist.
For tube amps you will need something around 4 amperes at least. I have a 10 ampere model and a 15 ampere unit as well. Tube amps draw more current on average than solid state equipment due to heater current. A 1 to 2 ampere quiescent draw would be normal for a tube amp, and that means a very high power bulb in your tester.
I know the lamp tester is cheap, but it has serious drawbacks and I personally do not think it is safe. I guess it is easier to smile and flip the switch not knowing what could happen.
-Chris
I highly recommend a variac for testing tube or solid state equipment. With a bulb limiter your energy to the circuit is unknown and he characteristics of the limiter may interact with the circuit. Using a variac you always know (and I mean know for certain) how much voltage you are supplying the circuit. It also allows you to run the circuit at reduced voltage so you can safely troubleshoot it.
I've serviced equipment for over 45 years now. The first thing I bought past my meter, 'scope and generator was a variac. Soldering iron came first, and hand tools. Since then I have bought larger variacs and made sure they were fully "metered" with output voltage and current meters. My current one has switchable meter functions, which I am not crazy about but it works. This one does measure leakage current easily. It's a B&K 1655 AC Power Supply. Got it cheap on Ebay so I couldn't resist.
For tube amps you will need something around 4 amperes at least. I have a 10 ampere model and a 15 ampere unit as well. Tube amps draw more current on average than solid state equipment due to heater current. A 1 to 2 ampere quiescent draw would be normal for a tube amp, and that means a very high power bulb in your tester.
I know the lamp tester is cheap, but it has serious drawbacks and I personally do not think it is safe. I guess it is easier to smile and flip the switch not knowing what could happen.
-Chris
Just *which* is your Country?
Why do you have 115-115VAC mains?
Is that normal in all of your Country or just in a specific place?
FWIW in the late 70´s early 80´s I used to live in a posh Buenos Aires neighbourhood which got electrified before others (think early 1900´s), our mains voltage is 220V and my home had 220V , no doubt, but coming from 3 x 220V three phase mains, no neutral. not normal 3 x 380V + neutral, getting 220V from any phase to ground (which is the European standard).
It was NOT 110-0-110 VAC either but hot to hot.
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I use a variac and meters, but really, when the OP has to ask if he needs two bulbs or not, I doubt the whole variac program will be intuitive to him. No offense intended. Further, I see thread after thread where someone keeps telling us he managed to "get the variac up to 90 volts before the resistors burnt up...again."
Shortcomings there may be, but "my light lit up bright" is darned easy to understand, even for a novice.
And of course the bulb affects circuit operation, but the use of a bulb is just for tracking down high current draw failures. It is not intended the amp will operate properly on the bulb. Once the draw failure is corrcted, we ditch the bulb.
Just my opinion.
Shortcomings there may be, but "my light lit up bright" is darned easy to understand, even for a novice.
And of course the bulb affects circuit operation, but the use of a bulb is just for tracking down high current draw failures. It is not intended the amp will operate properly on the bulb. Once the draw failure is corrcted, we ditch the bulb.
Just my opinion.
Perfectly valid Enzo. I was just offering up another method that the OP may not have considered.
When it comes to people working on things, I sure hope they have the basics. But knowing people, I'm sure there will be smoke no matter what.
When it comes to people working on things, I sure hope they have the basics. But knowing people, I'm sure there will be smoke no matter what.
For bulb limiters to be “safe” you really need multiple wattages. The lower the circuit power, the lower wattage bulb is needed so it limits at lower energy. A 60 watt works well for most home audio receivers, and 100 for larger dedicated amplifiers (up to about 200 wpc). Something lower powered might need a 25 watt bulb, a big pro amp might need 300. It’s not a hard and fast rule, and will not totally prevent things from smoking. But the usual sizes will prevent your house from burning down and will USUALLY prevent the power output transistors from being blown out (again) even if it takes out the drivers and half the small signal components. Those are cheap, and any resulting fire will be small enough that you can clean up the PCB and start again.
Not all amplifiers will come up properly on a bulb limiter. Some even misbehave if you turn it up slowly with a variac. Some amps will latch up to the rail or oscillate if the supply comes up too slowly, but the resulting DC current through the speaker will be safe if the bulb is sized appropriately (for the speaker).
I use a variac AND a bulb limiter. With a 60 and three 100 watt bulbs, screwing in only the one(s) needed. I got by with just the bulb limiter when I was primarily working on larger home audio and smaller pro amplifiers. When I stared doing TUBES the variac became necessary not optional. Then you can run at full applied line voltage with a significant quiescent draw, and still have soft limiting available for if something goes south several minutes into a test. It has on several occasions saved speakers from destructive low frequency oscillations while tuning in the frequency compensation. Solid state amps can also break into high frequency oscillations which can take out full banks if output transistors, and those problems often only show up at FULL rail voltage and under load with a real speaker. A bulb limiter alone and dummy load can lead you to a false sense of security thinking it’s fixed when it isn’t. And with just a variac alone, either situation could lead to blown amps/speakers.
Not all amplifiers will come up properly on a bulb limiter. Some even misbehave if you turn it up slowly with a variac. Some amps will latch up to the rail or oscillate if the supply comes up too slowly, but the resulting DC current through the speaker will be safe if the bulb is sized appropriately (for the speaker).
I use a variac AND a bulb limiter. With a 60 and three 100 watt bulbs, screwing in only the one(s) needed. I got by with just the bulb limiter when I was primarily working on larger home audio and smaller pro amplifiers. When I stared doing TUBES the variac became necessary not optional. Then you can run at full applied line voltage with a significant quiescent draw, and still have soft limiting available for if something goes south several minutes into a test. It has on several occasions saved speakers from destructive low frequency oscillations while tuning in the frequency compensation. Solid state amps can also break into high frequency oscillations which can take out full banks if output transistors, and those problems often only show up at FULL rail voltage and under load with a real speaker. A bulb limiter alone and dummy load can lead you to a false sense of security thinking it’s fixed when it isn’t. And with just a variac alone, either situation could lead to blown amps/speakers.
Hi wg_ski,
I mostly agree with you. I use a variac alone, but had tried a bulb limiter. I also use variable DC power supplies for some things.
As with anything, use of these devices requires some skill. You need to interpret the results. A variac will cover almost every need, but some times for specialized applications you may need to use a couple power supplies.
-Chris
I mostly agree with you. I use a variac alone, but had tried a bulb limiter. I also use variable DC power supplies for some things.
As with anything, use of these devices requires some skill. You need to interpret the results. A variac will cover almost every need, but some times for specialized applications you may need to use a couple power supplies.
-Chris