A demo of KCL!
Well if the power LED was glowing then you have probably competed the conversion!
The light bulb glows in standby for a few seconds and then extinguishes? That sounds a LOT like filter caps charging up.
It probably has some sort of soft start circuit. Usually the caps charge very quickly but if this is a large amp, then there may be a circuit that gradually charges them to avoid tripping circuit breakers.
After the caps charge, the load goes back down and the current through the amp diminishes to very little (just the standby turn on circuit which draws a few mA), and thus the current through the series lamp goes down to the same amount which is insufficient to light it.
By Kirchhoff's Current Law, the current through every element in a series circuit is the same. (its the voltage drops that vary...see Kirchhoff's Voltage Law which states that the sum of the voltage drops in a series circuit must equal the sum of the supply)
So lets say the standby circuit draws 6.0mA (a realistic scenario by the way), then 6.0mA flows through the bulb..... 6.0mA * 220V = 1.32W, clearly not enough to even begin to illuminate a 100W bulb.
If nothing has blown up or let out the magic smoke, I'd hook up a speaker and feed a small signal into it and see if it operates properly.
Well if the power LED was glowing then you have probably competed the conversion!
The light bulb glows in standby for a few seconds and then extinguishes? That sounds a LOT like filter caps charging up.
It probably has some sort of soft start circuit. Usually the caps charge very quickly but if this is a large amp, then there may be a circuit that gradually charges them to avoid tripping circuit breakers.
After the caps charge, the load goes back down and the current through the amp diminishes to very little (just the standby turn on circuit which draws a few mA), and thus the current through the series lamp goes down to the same amount which is insufficient to light it.
By Kirchhoff's Current Law, the current through every element in a series circuit is the same. (its the voltage drops that vary...see Kirchhoff's Voltage Law which states that the sum of the voltage drops in a series circuit must equal the sum of the supply)
So lets say the standby circuit draws 6.0mA (a realistic scenario by the way), then 6.0mA flows through the bulb..... 6.0mA * 220V = 1.32W, clearly not enough to even begin to illuminate a 100W bulb.
If nothing has blown up or let out the magic smoke, I'd hook up a speaker and feed a small signal into it and see if it operates properly.
Nothing blew up, so I tried it with an ipod as an input and 1 speaker connected as a load. Only tested at low volume, but music played fine at 220V and nothing blew up.
However, my 40W bulb was glowing (not at at full brightness) in the lightbulb tester, regardless of the input or the volume of the music.
Is this current draw normal? Am I in the clear?
However, my 40W bulb was glowing (not at at full brightness) in the lightbulb tester, regardless of the input or the volume of the music.
Is this current draw normal? Am I in the clear?
"So lets say the standby circuit draws 6.0mA (a realistic scenario by the way), then 6.0mA flows through the bulb..... 6.0mA * 220V = 1.32W, clearly not enough to even begin to illuminate a 100W bulb."
A Hafler DH500 wired for 240V draws 1A at idle.
When testing at 120V I use a 150W lamp, and it glows pretty solid after a brief turn-on flash.
Most smaller 120V amps will power up OK with a 75W bulb, and have about 2/3rds of their nominal ±V.
I don't test class A or tube amps, so don't ask.
A Hafler DH500 wired for 240V draws 1A at idle.
When testing at 120V I use a 150W lamp, and it glows pretty solid after a brief turn-on flash.
Most smaller 120V amps will power up OK with a 75W bulb, and have about 2/3rds of their nominal ±V.
I don't test class A or tube amps, so don't ask.
mixersoft said:
Hi,
With that low current (6mA) passing, the light bulb will not have 220Vac across it.
It may be as low as 5Vac or upto 50Vac.
The power dissipated in the filament <<1W.
That glowing filament must have a lot more than 6mA to be getting that hot.
Disconnect everything from the transformer secondaries, even the rectifier. Check the bulb again. Measure the Vac across the transformer primary.
Add the rectifier and smoothing and run through the same checks.
Add one amplifier, short the input RCAs, disconnect the speakers, check again,
Add the second amplifier, check again.
Measure the mVac and mVdc at the speaker terminals.
Remove the short from the power amplifier input terminals and repeat the speaker terminal measurements.
Post your results.
Sorry for the delay, had some stuff come up.
I can't disconnect the rectifier without bringing out the soldering gun. But the amp has 5 pots to turn down each amp/channel individually.
Here is what I found so far.
When powered up, the 40W Bulb is lit.
Voltage across the primary = 92vac, 46vac across each winding in series
Voltage across speaker terminal = 2.6mVdc, can't measure ac with my DMM. This is true regardless of whether the input is shorted or not, and regardless of the settings for the 5 pots.
Does that say anything, or should I get out the soldering gun?
I can't disconnect the rectifier without bringing out the soldering gun. But the amp has 5 pots to turn down each amp/channel individually.
Here is what I found so far.
When powered up, the 40W Bulb is lit.
Voltage across the primary = 92vac, 46vac across each winding in series
Voltage across speaker terminal = 2.6mVdc, can't measure ac with my DMM. This is true regardless of whether the input is shorted or not, and regardless of the settings for the 5 pots.
Does that say anything, or should I get out the soldering gun?
AndrewT said:
Tthe voltage to each of the 5 amplifiers is 138.5vdc
The voltage across the each of the 5 capacitors is 69vdc - is that the same as the voltage after the rectifier?
Do these numbers make sense? I can't reach the secondary windings without disassembling. I'll get to that in a little bit.
ooh. that is a difficult question to answer, isn't it? Do I have to risk an explosion to find out?
Let me just repeat what I have done so everthing is clear:
I'd rather not risk an explosion. Does it make help for me to measure the voltage across the caps and to the amps in the original 110V configuration -- i.e. with the primary windings connected in parallel and 110V from the mains?
Let me just repeat what I have done so everthing is clear:
- 220V from the mains
- 40W light bulb tester is connected and lit during all tests
- 92VAC across the transformer primary, 46VAC for each winding
- voltage across the transformer secondary = unknown
- 69vdc across the capacitors
- 138.5vdc to the amplifiers
- 2.6mVdc across speaker terminal with inputs shorted
I'd rather not risk an explosion. Does it make help for me to measure the voltage across the caps and to the amps in the original 110V configuration -- i.e. with the primary windings connected in parallel and 110V from the mains?
Here is what I get in 110V config:
* 110V from the mains
* 100W light bulb tester is connected and lit during all tests
* 60VAC across the transformer primary
* voltage across the transformer secondary = unknown
* 26.5vdc across the capacitors
* 53.5vdc to the amplifiers
* 5 mVdc across speaker terminal with inputs shorted
STANDBY MODE
* 116VAC across the transformer primary
* bulb is NOT lit
* 69.1Vdc across the caps
* 138.3vdc to the amplifiers
* -0.28Vdc across speaker terminal with inputs shorted
The 110V config is the original (working) configuration. I guess I'm surprised that the bulb is lit. That means there is a steady current drawn whenever the amp is on, correct?
Its funny how the 110 Standby DC voltages match the 220 operating DC voltages. Is that a coincidence? I didn't measure the standby voltages in 220V config. would that be helpful?
* 110V from the mains
* 100W light bulb tester is connected and lit during all tests
* 60VAC across the transformer primary
* voltage across the transformer secondary = unknown
* 26.5vdc across the capacitors
* 53.5vdc to the amplifiers
* 5 mVdc across speaker terminal with inputs shorted
STANDBY MODE
* 116VAC across the transformer primary
* bulb is NOT lit
* 69.1Vdc across the caps
* 138.3vdc to the amplifiers
* -0.28Vdc across speaker terminal with inputs shorted
The 110V config is the original (working) configuration. I guess I'm surprised that the bulb is lit. That means there is a steady current drawn whenever the amp is on, correct?
Its funny how the 110 Standby DC voltages match the 220 operating DC voltages. Is that a coincidence? I didn't measure the standby voltages in 220V config. would that be helpful?
Sorry for the delay again, got caught up with something else.
But I just realized that I should have done the 110 test with the *SAME* light bulb.
When I do that, I discovered that the voltage across the caps and to the Amps are exactly the same:
121VAC at the mains w/ 40W (220V) light bulb in series:
* 44.5 VAC across the primaries (2 windings in parallel)
* 19.3vdc across the capacitors
* 38.7vdc to the amplifiers
234VAC at the mains w/ 40W (220V) light bulb in series:
* 91.6VAC across the primaries
(45.7VAC across each winding in series)
* 19.6vdc across the capacitors
* 39.3vdc to the amplifiers
If I get the same voltages in the DC circuits, can I assume the 220V config is correct?
I suppose this assumes the resistance/impedence in the output (rectifiers/caps/amp) circuity is constant, correct?
But I just realized that I should have done the 110 test with the *SAME* light bulb.
When I do that, I discovered that the voltage across the caps and to the Amps are exactly the same:
121VAC at the mains w/ 40W (220V) light bulb in series:
* 44.5 VAC across the primaries (2 windings in parallel)
* 19.3vdc across the capacitors
* 38.7vdc to the amplifiers
234VAC at the mains w/ 40W (220V) light bulb in series:
* 91.6VAC across the primaries
(45.7VAC across each winding in series)
* 19.6vdc across the capacitors
* 39.3vdc to the amplifiers
If I get the same voltages in the DC circuits, can I assume the 220V config is correct?
I suppose this assumes the resistance/impedence in the output (rectifiers/caps/amp) circuity is constant, correct?
With +-70V rails it seems like a quite big amp. A 40W bulb isn't likely to allow that to start up if there is sensible bias in the output stage.
BTW: With a series lightbulb the voltage will look more like a square wave instead of sine if there is enough current for the light bulb to light up. What does the value displayed by your meter mean in that case?
BTW: With a series lightbulb the voltage will look more like a square wave instead of sine if there is enough current for the light bulb to light up. What does the value displayed by your meter mean in that case?
I looked at my earlier numbers and I must have done something different, because the latest measurements don't match up.
I did notice that STANDBY mode gives different results:
STANDBY mode:
234VAC at the mains w/ 40W (220V) light bulb in series:
* bulb NOT lit once caps have been charged
* 215VAC across the primaries
(107VAC across each winding in series)
* 60vdc across the capacitors
* 121vdc to the amplifiers
ON mode:
234VAC at the mains w/ 40W (220V) light bulb in series:
* 91.6VAC across the primaries
(45.7VAC across each winding in series)
* 19.6vdc across the capacitors
* 39.3vdc to the amplifiers
121VAC at the mains w/ 40W (220V) light bulb in series:
* 44.5 VAC across the primaries (2 windings in parallel)
* 19.3vdc across the capacitors
* 38.7vdc to the amplifiers
BTW, these figures are with all the output stages connected.
I'm not sure what to say about the square wave issue, I only have a DMM so I can't see the waveform.
I did notice that STANDBY mode gives different results:
STANDBY mode:
234VAC at the mains w/ 40W (220V) light bulb in series:
* bulb NOT lit once caps have been charged
* 215VAC across the primaries
(107VAC across each winding in series)
* 60vdc across the capacitors
* 121vdc to the amplifiers
ON mode:
234VAC at the mains w/ 40W (220V) light bulb in series:
* 91.6VAC across the primaries
(45.7VAC across each winding in series)
* 19.6vdc across the capacitors
* 39.3vdc to the amplifiers
121VAC at the mains w/ 40W (220V) light bulb in series:
* 44.5 VAC across the primaries (2 windings in parallel)
* 19.3vdc across the capacitors
* 38.7vdc to the amplifiers
BTW, these figures are with all the output stages connected.
I'm not sure what to say about the square wave issue, I only have a DMM so I can't see the waveform.
Watch out!