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Old 7th November 2012, 02:52 AM   #21
turk 182 is offline turk 182  Canada
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Default lamp tester

lets not compromise between safety and knowledge.sometimes we need to stop and take a common sense approach to information we get and run with it.
in the case of the homebrew lamp current limiter we're talking about which can be a useful piece of test equipement. one has to stop and ask themselves,"do i understand what this device is and what it is intended to do and how to apply it. do i understand fully any limitations it has." if this is you seek more information.sometimes what we don't know can have disastrous consquences
there is some glaringly obvious bad information in this thread about these devices and how to use them
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Old 7th November 2012, 04:33 AM   #22
Vrystaat is offline Vrystaat  South Africa
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Default New amp startup

So it would be the best to use a lamp (100W)in series with the amp in conjunction with a variac ? If an amp should work on 55V DC after rectification and you start the variac up on a much lower voltage, could some of the semiconductors be damaged due to a too low voltage or should you set the variac to a voltage , say 40Vdc after rectification when you first switch on ? Is it also then necessary to put 100 Ohm resistors in the place of the rail fuses ? Your input will be appreciated.

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Old 7th November 2012, 06:27 AM   #23
Coconuts 500 is offline Coconuts 500
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Originally Posted by DF96 View Post
1 - agreed
2 - if only that were true - magazine articles can contain errors - it is astonishing how confidently some people can write about subjects which they are ignorant of - I am not talking about the minor errors which all authors make or debatable points, but genuine profound ignorance of a subject
He he, I was given a bunch of hifi magazines, the first one I started looking through claimed that music sounds better when played through an usb memory rather than a hard disk - and that there were differences in sound between different kinds of usb memories (of course, the more expensive ones sounding better). All in a totally serious (even superior "duh, obviously this is the case" like) tone. This forced me to throw the entire stack of magazines in the trash.

Sorry for going off topic. Just had to share.
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Old 7th November 2012, 08:41 AM   #24
turk 182 is offline turk 182  Canada
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let me begin by stating i don't like the name "lamp tester" i prefer "homebrew current limiter"
in answer to your first question yes it's a good idea to have a series lamp in conjunction with your variac for a few reasons.
let's take a moment to analyze this
in a series connected circuit current flow is determined by the sum of resistances in series
now in the homebrew limiter the wattage of the lamp wattage determines the current (as an example a 100 watt lamp at 120 volts the current would be 0.833 amps a 50 watt lamp the current is 0.4166 amps)so now let's look at how this applies to our limiter and our device under test(your brand new chip amp or that crusty old tube amp you want to revive) if our device under test has a dead short somewhere or a bad fault it's essentially the same as a low value resistor which would change the value of current draw in our series circuit lighting our limit lamp nice and bright because the voltage drop is now across the limit lamp
now using this requires a little estimation of what normal current draw should be in our test device. in a linear solid state amp with no faults at idle it shouldn't be drawing a whole lot the limit lamp would be off or at best a very faint glow in the case of our tube amp we can expect a little more draw because of the heater circuits
to recap a hard short bright light a normal non defective unit faint glow or low intensity
the same principle applies to the substitution of fuses with 100 ohm resistors if you monitor the voltage across them you can exprapolate the current draws in the plus minus rails of the device if there's a big difference watch out there's a problem
as to damage to semi's in current starvation or low voltage i don't see a problem (but i may well be corrected in this instance) i can tell you that using the homebrew limiter with switch mode supplies and sometypes of the newer class d or t amps can problematic as some of these devices can be intolerant of having their operating point messed with
i like using this lamp limiter when i'm going to power up a device in which i've replaced output devices like expensive T03 transistors but can't be sure might still contains a driver stage fault or leaky filters or assess an old tube amp which may or may not be ok because the lamp can give almost instantaneous visual cue from flickering intensity (a sign of instability or breakdown) to monitoring short or long term trends as indicated by changes in the lamp filament intensity
well i hope that this helps to illuminate you (no pun intended)

p.s. you mentioned in your post about an amps voltage after rectification the homebrew because it's ahead of everything would even help show gross diode faults in a supply

Last edited by turk 182; 7th November 2012 at 08:54 AM.
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Old 7th November 2012, 10:38 AM   #25
DF96 is offline DF96  England
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Originally Posted by turk 182
there is some glaringly obvious bad information in this thread about these devices and how to use them
Would you care to identify this "glaringly obvious bad information"? Ideally your response should use the normal English conventions of sentences etc.
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Old 7th November 2012, 11:18 AM   #26
AndrewT is offline AndrewT  Scotland
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Originally Posted by Vrystaat View Post
So it would be the best to use a lamp (100W)in series with the amp in conjunction with a variac ? .............
The Variac usefulness and the bulb tester usefulness are very different.
They do different jobs very well.
They are not interchangable nor are they compatible to conjoined use.

The bulb tester is a fool proof way for checking that gross wiring errors are there, or not there.

The Variac cannot do this effectively.
yes it's a good idea to have a series lamp in conjunction with your variac for a few reasons.
I completely disagree.
Your explanation that follows does not detail where or how the conjoined bulb tester and Variac offer an advantage.

The Big Advantage of the bulb tester is that it automatically inserts the protection "current limiter", that is Mains voltage rated, to prevent catastrophic damage downstream. I always start with a low power bulb, I have just bought some 25W bulbs specifically for this use and compatible with the bulb holder I have. (my previous 25W bulbs need an e15 holder which I have not found yet.

Normally I start at 40W and progress through to 150W, if necessary, to get the circuit up to almost full operational voltage, checking the circuit at each stage for smoke, smell, voltages, currents, etc. But this progressive increase in bulb power is only required where the quiescent power draw brings on the limiting effect of the PTC inside the bulb envelope, i.e. it start to glow. If the bulb filament stays cold or near so, then the resistance in the primary circuit passes quiescent current safely to the transformer.

You are right in one aspect. Don't use a bulb tester when you are not using a mains transformer. The transformer and it's wiring is what the first line of checking that the bulb tester is useful for !!!!!!
regards Andrew T.

Last edited by AndrewT; 7th November 2012 at 11:32 AM.
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Old 7th November 2012, 11:25 AM   #27
turk 182 is offline turk 182  Canada
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what's wrong with my sentence structure?
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Old 7th November 2012, 12:05 PM   #28
dimkasta is offline dimkasta  Greece
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With buttons and parallel lamps it gets more complicated than it needs to be.

I have built my own with a simple cable like the ones above.

It is really easy to change the bulb if necessary for a project and it is really really easy to remove it and plug the project straight to the wall.
I don t see a reason why to build something with switches etc that are only "convenience" additions and are very likely to create problems if something is overlooked.

If you really need a switch, I would use a switched socket on the wall for the on-off, but I wouldn't wire a bypass switch. We really do not want one extra thing to have to remember when we are dealing with mains ...
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Old 8th November 2012, 01:40 AM   #29
nigelwright7557 is offline nigelwright7557  United Kingdom
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A 40 watt bulb is great for just powering up class AB and D amps.
But the bulb will come on if any serious power is taken.

I found for SMPS testing at least a 100 watt bulb is required or the SMPS keeps resetting itself under load.

I have a test rig for testing new amplifiers and I just put in a low current transformer so it will overload before blowing up transistors. If there is a problem I can almost always hear hum in the speaker.
PCBCAD51 pcb design software. 2018 version out now. https://www.ebay.co.uk/sch/i.html?_f...nload&_sacat=0
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Old 8th November 2012, 01:57 AM   #30
turk 182 is offline turk 182  Canada
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i wish i knew how do that quote thingy. i've looked through the frequently ask questions to see if i could learn how to do that
can anyone help me with that?
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