I have an old stereo amplifier in whch some of the indicator lamps have blown. Unfortunately two of these are enclosed in the VU meters, I'm wondering if it's possible to open up the meters and replace them, if not, hot glue some replacements to the exterior.
Picture:
TIA
Dave Australia
From your picture I cannot see enough about the meters to answer you. If there is seam or obvious means to open the case I would try to replace the lamps. By the looks of the circuitry, if a lamp burned out in that time period I would suspect a tech would replace the meter, but I could be wrong.
Tom
6
ace
I haven't pulled the meter out to inspect it, will do it tomorrow and take some more pictures and link them here.
Dave Australia
Drill(or melt with solder iron) 1 or 2 holes in the sides of the VU meters, then glue white LEDS in the holes. Keep the current in the LEDS at 30-50 %, and they last forever. I have done that in my radio, where the tuning senselights burned out.
That style of meter is often held together at some point with sticky tape. Remove and check.
Graham
Upon closer inspection, I found that the lamps simply popped out of the meter's side, the bulbs are about twice the side of a grain of wheat bulb. I replaced it with a clear incandescent bulb.
Dave Australia
How do I check the output power of this amp? There is no indication anywhere as to what the power output is. It runs fine on a pair of modern Pioneer 20w speakers, but I'd still like to know the output., The power input is 85w max at 240v if that helps.
Dave Australia
80W in 40W out, sounds pretty good for class AB.
Bon't expect a waggly meter to help you !
Graham
Why not? That's how I did it when I was a kid, before I had a scope. But first you have to make a dummy load, some humongous 8ohm resistors.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Another question I have about this amp. There are four (output) transistor mounted on a large heatsink at the rear of the chassis, two of these have two core wires glued on to them. These wires are soldered in holes on the PC board that have the diode ( >| ) symbol. What are the purpose of these wires? I have the schematic that is glued to the bottom of the unit, I can remove the bottom and scan it if it helps.
On music, mechanical meters tend to under-read the actual power since they can't repond to peaks very well. They'll give an idea of average power but not peak (which tells if your amp is being overdriven).
Graham
Glued ? Do they solder to anything ?
Bizarre.
Graham
-- I\'d guess that what\'s glued onto the transistors are diodes and that they\'re being used as temperature sensors. JF
For bias temperature compensation. That makes sense.
Graham
Thermo protection diode..
can't
Old trick: Feed it with a few hundred Hertz or if too lazy to build an oscillator 50/60Hz from a doorbell transformer. Additional hi-Z resistive divider across the output so you can listen with headphones without blowing your ear drums out. Crank up until distortion is heard
-> read meter -> place dummy load on back porch to cool off -> done.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Often they are directly in the bias circuit so it tracks with temperature changes (somewhat), no loop.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Temperature sensor,to stop over heating.
86
I think you're right. I took another, closer look under the hood of the amp, they are not wires like I thought, but leads of a component covered in clear insulation. And since that component is green, with a black band, I take it to be a diode. The reason I didn't see the diode before, was because it's covered in glue, which has dried out on one transistor and the diode is hanging in midair. Should I just superglue it back on, or is there a special type of glue for this?
Dave Australia
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