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Dim Bulb Tester Build and How-To

Some power bars can be rewired for use as a DBT. I reconfigured this one with six outlets in parallel for bulbs and one in series for the test device. I use it with 40 and 60 watt bulbs in various combinations to provide an equivalent lamp of 40 to 360 watts in 20 watt increments.

DBT.jpg
 
The reason I asked this question is because I read a thread from Radio Museum about building a DBT and the author said that if I can't find a bulb 1.5 times greater then the receiver wattage, which in my case is a SX1000TD at 130 watts, that I could plug a power strip with multiple smaller wattage bulbs into the DBT. If that's true it would come in handy since high watt incandescent bulbs are illusive.
 
True. It is rated at 50 wpc. But total watts is 120 @ 8 ohms. I assumed I should use total watts rather then wpc to calculate the bulb wattage in the DBT. I guess I'm wrong?
 
I think you will be fine with a 60 or 75 watt bulb.

It's hard to know what the recommendation of a bulb with a wattage rating of 1.5x the amp's power rating was based on.

BTW, for practical purposes, the RMS rating is is the best representation of useful power output capability for an audio amp. Effectively, it tells you how much power the amp can deliver on a continuous, or average, basis.
 
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I finily finished this DBT.
It started as, - well somewhat as a Mr. Carlson current limiting, variac clone.
I found out the isolating transformer was a ferroresonant transformer and could not be in the circuit after the variac. This I found out when connecting and checking it for the first time. With the great help and knowledge here on AK, I was able to utilize it in the circuit. This time it was wired in front of the variac. The contraption works great. It looks ominous but behaves like it should. The mutation is the rework in swapping the transformer operation in the circuit and my Yankee frugalness.
I was determined to use as little money as possible. The isolation transformer and variac were the big purchases only costing $30 combined (Garage sales). The electrical supplies? Mostly free.

This is the thread I started with the question about the transformer:
https://audiokarma.org/forums/index...a-isolation-transformer.874719/#post-12843934

DSC05633.JPG
 
LesE said:
Some power bars can be rewired for use as a DBT. I reconfigured this one with six outlets in parallel for bulbs and one in series for the test device. I use it with 40 and 60 watt bulbs in various combinations to provide an equivalent lamp of 40 to 360 watts in 20 watt increments.

View attachment 1516280
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Thats a good idea since large wattage incandescent bulbs are real hard to find. If I do not find a suitable power strip to use just wiring several duplex outlets in parallel would work as long as its still in series with the test device.
 
All this is great AC wiring information but could some one put up a photo of where it would connect to a receiver input if used for testing bias settings?
 
So finally built one with the parts from my garage mostly other than the PVC enclosure and the plug socket converter, all follow @EngineerNate instructions including testing. I can follow instructions but have very limited electronics background and knowledge.
I have no confidence on my built so I got one test unit, a JVC RX 5V receiver which I acquired recently, it plays music through aux or tape input but the tuner display and all function keys related to the tuner are not responding at all. Don't know the causes but seem like something related to power supply or the control IC is totally shot. Also at the start up, there is this skipped beat noise until the unit "warm up" like 5, 10 mins of play. It sounds nice to me but with all the issue I cant resolve yet.
Any way, when I power it through this DBT unit, the bulb flash for quick 1 seconds and then everything just goes quiet. no power at JVC, no dim light, nothing.
So I pull out another working receiver, power through DBT, then strong bulb flashing then down and the receiver powers up, so the DBT unit I built seems "working" properly?
So can someone explain why the JVC not powered up through DBT but actually works and plays music? Thanks a lot.
P.S. If this is not the right place to post my DBT related problem, please let me know.
 
EC1 said:
So finally built one with the parts from my garage mostly other than the PVC enclosure and the plug socket converter, all follow @EngineerNate instructions including testing. I can follow instructions but have very limited electronics background and knowledge.
I have no confidence on my built so I got one test unit, a JVC RX 5V receiver which I acquired recently, it plays music through aux or tape input but the tuner display and all function keys related to the tuner are not responding at all. Don't know the causes but seem like something related to power supply or the control IC is totally shot. Also at the start up, there is this skipped beat noise until the unit "warm up" like 5, 10 mins of play. It sounds nice to me but with all the issue I cant resolve yet.
Any way, when I power it through this DBT unit, the bulb flash for quick 1 seconds and then everything just goes quiet. no power at JVC, no dim light, nothing.
So I pull out another working receiver, power through DBT, then strong bulb flashing then down and the receiver powers up, so the DBT unit I built seems "working" properly?
So can someone explain why the JVC not powered up through DBT but actually works and plays music? Thanks a lot.
P.S. If this is not the right place to post my DBT related problem, please let me know.
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Trying to play music or test functionality on DBT is counter-productive. Its purpose is to protect the amp and some of its components from an over-current situation after making changes that put it at risk. Once it passes the DBT test you are done with the DBT. Sometimes, if you are concerned, you can check some power supply voltages while on the DBT, however you must recognize that your AC voltages, unregulated DC voltages, and maybe/probably some regulated DC voltages will be lower than spec. How much lower depends on what wattage bulb you are using and how much 'housekeeping' power the amp draws.
 
yes, I am using Incandescent bulb. 60w and 75w, both react the same when I connected to the JVC receiver.
No, no speakers connected and I am not playing the music with the DBT unit.
I am just wondering why it behaves like that when I tested with this JVC receiver?
 
EC1 said:
I am just wondering why it behaves like that when I tested with this JVC receiver?
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Different units behave differently, it will depend on how much load it tries to pull through the DBT, and how the power supplies are designed.
Some Pioneers, with higher 'housekeeping' current draw have trouble with the protection relay pulling in on DBT, because the power is limited by the DBT (that is its job). A higher wattage bulb will pass through more power.

This is a 60W bulb on a fully functional (no music playing) SX-1050:

60wCrop.jpg

The protection relay was markedly slower to pull in.

Here is 120W (two 60W in parallel) bulbs, same amp:

120W_crop.jpg

The relay was much quicker to pull in, but still slower than full mains voltage.

You could probably figure out why your JVC does what it does, as an intellectual exercise, but if it works fine on full power I would not worry about it.
 
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But if I had the DBT unit to start with this JVC, I probably will not power it up and play it once I see the abnormal behavior of the test, right? Again, as I mentioned, I don’t know that much and just try to learn little by little. I am assume this DBT unit is functioning properly based on the other receiver I tried it on so the unit can be used later on. Thx.
 
The DBT test is just to see if you have an overload on the power input, the bulb will flash bright as the power is turned on and the empty power supply caps draw a surge of current, then it dims down after the caps are charged. If you see that, it has passed the DBT test and can be plugged into full power. If the lamps stay bright (or pulses) you have a problem that needs troubleshooting. There is no reason to expect an amp to behave normally while on a DBT, Some may appear almost normal, some do not, but you cannot expect normal amp behavior while the DBT chokes off the input power.
The DBT is a protection device, and problem indicator, but it does not 'help' figure out what is wrong beyond its simple indication.
From your descriptions your DBT is working correctly.
If the JVC is not blowing fuses or smoking on full mains power it just needs regular troubleshooting done to figure out what is wrong with it. It may indeed have power supply problems, but you will need to get out the Service Manual, schematic, and your meter, and dig into it. We all were where you are at at some time in the past, enjoy learning and being challenged, AK will help!
 
I'm sorry for my dumb question, why do we need this dim bulb tester when the power strip already has a circuit breaker to interrupt the electric current in case of an overload or a short circuit?
 
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