Bulb Limiter test

[angelodp]

I assume that the Bulb Limiter Test is good for any tube amp. I just completed a 5E3 and I am ready to test it.

ange

[Bob-I]

I assume that the Bulb Limiter Test is good for any tube amp. I just completed a 5E3 and I am ready to test it.

ange

yes

[paolojm]

Out of interest; is it safe to use a bulb limiter to test solid state equipment?
A friend had an old stereo which he thought was valve based. It was blowing fuses but I was fearful of potentially causing further damage by using a limiter.

[Structo]

The lower the wattage the light bulb used in the limiter, the less current supplied.

I believe I read where a 25w bulb limits the current to around 250ma or 1/4 ampere.

Solid state gear has power supplies and filtering as well so, the same symptom would apply, that is, the light bulb staying bright would indicate a short.

[paolojm]

I worked the current limit out to be about 104mA @ 25W around where I'm from (240Vac), guess you're on 120Vac?
I was just worried that running SS componants on too low a voltage could cause damage to them? I'm pretty sure that switching circuits etc. would not work due to gate voltages not being made etc. but not sure if actual damage could be done.

[gahult]

The bulb limiter, I believe, is just a safety device used on initial start up to take the load and indicate by glowing bright that you have a short the needs to be corrected.

If it goes bright and then dims to a soft glow there are no shorts and should then be removed for further tests and voltage checks as it will effect the readings.

Gary

[paolojm]

The bulb limiter, I believe, is just a safety device used on initial start up to take the load and indicate by glowing bright that you have a short the needs to be corrected.

If it goes bright and then dims to a soft glow there are no shorts and should then be removed for further tests and voltage checks as it will effect the readings.

Gary

I know what it is and use one regularily for valve amp repair, the question is whether or not it is safe to use on SS amp, stereos etc.

[Kregg]

If you ever get the chance watch the show "How it's Made." I think every electric/mechanical device goes through a slow start up and a series of tests before they are shipped out (though they don't always show the test step). This includes fuses, light bulbs and transformers. Remember, even a computer is an amplifier to some extent.

[mhuss]

Yes, it's safe to use with SS equipment. The D.U.T. likely won't work well (or at all) with the bulb in series, but as has already been said, it's just a quick-and-dirty overload check.

--mark

[paolojm]

Yes, it's safe to use with SS equipment. The D.U.T. likely won't work well (or at all) with the bulb in series, but as has already been said, it's just a quick-and-dirty overload check.

--mark

Cool thanks.
That's pretty much what I thought, but I was afraid that certain SS devices may be damaged by operating them under their speced voltage range.

[fperron_kt88]

Just wanted to add another point of view...

I believe not *all* SS equipment are happy with lower voltages. For example, anything powered through a DC-DC converter might go into high-current or motorboating if not carefully protected by design. Think high-power modern bass amps in 1U formats...

Most devices have brownout protection and enough hysteresis for their defined *general use*, but not necessarily in all conditions you might be exposing them to... and sticking energy-storing devices in series with these could certainly diminish stability margins if you hit the sweet spot.

Again, not trying to stirr-up the water but just trying to offer another opinion...

[paolojm]

Ah dammit, I was afraid someone would that.
Would such SS devices exist in audio circuits?

[fperron_kt88]

Well, most "international" power supplies for an example (think laptop). Things like a pedal board power supply or a keyboard power supply, maybe... You can notice they have a minimum input AC voltage in. However, I would bet those are well protected from brownout and over-current conditions internally.

Any high power amp in very small formats (1kW bass amps in a 1U rackspace) could be much more finicky. I believe these are marketed as transformerless designs, whatever than means...

One thing you can always do: look for minimum voltage rating specifications and respect them. This should get you out of trouble... As a general rule, keep inductance low in the input path. Problem with the bulb comes from the higher cold resistance: perfect for a slow start when low voltage is good, but this can trigger all sorts of fancy over-limit conditions in the initial power-up sequence of these things.

Most DC-DC converters heat up fast and sing like lobsters if some parts go in higher current modes. Not always pretty...

What SS equipment are you debugging? Do you feel confident enough with electronics to identify a specific power supply design? Maybe better to defer that one to somebody you trust with electronics...

Again, just my thought...

[fperron_kt88]

thinking out lound again... your SS equipement has all its fuses properly installed, right? The electrical panel is setup properly with fuses of the proper values for whatever electrical code/wire size, right (assuming it connects to the grid...)?

What is preventing you from operating the SS equipement as it is supposed to be operated?

In other words, what leads you to believe that there is something in there that could prevent it from starting properly, as designed?

[paolojm]

Using a bulb limiter drops the operating voltage in the amp proprtional to the current drawn throught the bulb. Valve amps typically have half the normal operating voltage, which is fine for them.
Something at the back of my mind was telling me that some SS devices dont like being operated under voltage though.