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Another Dim Bulb Tester Question

C

Champ

Active Member
I have a fully functional DBT and recently tested it with a small Lafayette LA-224T solid-state amplifier. The amp is rated at a 30-watt power draw and has a relatively low output.

When I connect the DBT, there’s no light at all, regardless of which bulb I use — I’ve tried 25W, 40W, and 75W bulbs with the same result.

What’s happening here? This is the first time I’ve powered up such a small amplifier using a DBT, so I’m curious whether the draw is simply too low to illuminate the bulb, or if I might be missing something else.

Any thoughts or explanations would be appreciated.
 
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Either the amp is not drawing any power or the inrush is so small that it doesn’t warm up the filament. The smaller bulbs are for smaller draw units.
Try it on line power as it passes the DBT.
 
Of those bulbs the 25W would be the most likely to get bright, or flash some. Higher wattage bulb = pass more current.

Does the unit turn on? If the main filters are small, and perhaps they do not bleed down when off, you won't see much for a bulb flare. Are most of the lights burnt out? Will lead to less of a draw.

But generally small receivers draw less. Small receiver with 75w bulb = almost no chance of a flare unless a short. Big receiver with small bulb = full roar always. You will see the relation.
 
Bradbrews said:
Either the amp is not drawing any power or the inrush is so small that it doesn’t warm up the filament. The smaller bulbs are for smaller draw units.
Try it on line power as it passes the DBT.
Click to expand...
Thanks Bradbrews! No filaments, Solid State. "Try it on line power as it passes the DBT" please elaborate. After trying to figure this out I did plug it in to the mains directly and it is fully functional. I want to do a restoration and need to be prepared to use the DBT when checking my work.
 
Warren-Oates said:
Of those bulbs the 25W would be the most likely to get bright, or flash some. Higher wattage bulb = pass more current.

Does the unit turn on? If the main filters are small, and perhaps they do not bleed down when off, you won't see much for a bulb flare. Are most of the lights burnt out? Will lead to less of a draw.

But generally small receivers draw less. Small receiver with 75w bulb = almost no chance of a flare unless a short. Big receiver with small bulb = full roar always. You will see the relation.
Click to expand...
Amp actually works and is fully functional. Just trying to protect the amp when restoring it. The 25W bulb is recommend then? Because that was my first go too. Not even a whimper of a flash.
 
Champ said:
Amp actually works and is fully functional. Just trying to protect the amp when restoring it. The 25W bulb is recommend then? Because that was my first go too. Not even a whimper of a flash.
Click to expand...

Does the amp work when connected through the DBT?

Are you sure the DBT is wired correctly?
 
whoaru99 said:
Does the amp work when connected through the DBT?

Are you sure the DBT is wired correctly?
Click to expand...
Power light is on through the DBT. Yes, the DBT is working. I have used it for several years and tested it on a high power amp and it works.
 
Only thing I can think of is that the main caps in the power supply are so far out of spec that they are not charging up to capacity. I will check to see how far out they are. I am sure they are not good. Amp looks all original, early 1960's.
 
Maybe... but they're certainly not bad in the manner to present low resistance.

At 30W rated draw, bearing in mind that could be max draw or at some level of output materially above idle, it just might not be enough anyway to light up a 25W lamp at idle.

Do you have a Kill-A-Watt or something like that to measure actual power draw?
 
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Ordering a Kill-A-Watt today. What kind of wattage would I be looking at on idle and I assume no load and volume turned all the way down.
 
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