• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Caps...what the...

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
CAPS

Hi,

Yes,that looks like it to me.
Any idea about the value of the resistor across those caps (you will have to unsolder it to measure) if any?
Or if you have a circuit diagram,that would help too.Sometimes they are put where you don't expect them...

Cheers,
 
Hi Rino

The discharge time of the B+ filters can be affected by several things. Do you have any voltage dividers on the B+? Remember, tubes will still conduct for a short time after the filiment supply is shut off, up to several seconds depending on the tube.

The discharge time depends on the amount C in the filter and the load. Try measuring the DC resistance from B+ to ground. The lower the resistance, the faster the discharge will be. :att'n: Remember to make sure the power supply caps are discharged before you connect your Ohm meter. :att'n: :bawling: Connect the + Ohm meter lead to the +cap terminal and the - meter lead to ground. The reading will jump to a low reading and then, as the meter charges the caps, the reading increase. When the Ohm meter reading stops changing that is the resistive load on the power supply.

It's just a good old RC time constant the determines discharge time.

Later
Bruce:geezer:
 

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
CAPS

Hello Rhino,

Is that the Lux MQ3600 given you trouble again?
If so,I think I can find the circuit diagram on the net.
Still,Bruce's proposed method is valid so you can check that way.
One thing to keep in mind though is that if filter caps don't keep their charge they usually don't filter too well either,so you have should hear some hum on the speakers.And since you always said they were sounding fine...:rolleyes:

Cheers,
 

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
CAP

Fellows,

That's not the correct way to measure a capacitor.
The component you are trying to measure must be disconnected from the B+.
Then it should be discharged and measured with a capacitance meter.
An Ohm reading will also give you an idea about it's condition.
All this under the assumption that all caps are the same in value and voltage?

Rgds,:cool:
 
Hey Folks,

I know nothing of the amp in question, but I did notice with one of my PS designs that with a large inductance (5H) when the power went off, the caps discharged quite quickly. 3-6 seconds. Could it be that the collapse of the magnetic field causes a back emf that discharges the capacitors quickly? I did notice that when I changed to a 1.5H choke in the same PS the caps discharged noticably slowly. That is music kept playing for 20-30 seconds.

Just aksin.

Gabe
 

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
CAP DISCHARGE

He Gabe,

Depending on how that choke is connected in the PSU and its series resistance,maybe one will then discharge the caps faster than the other.
But a choke causing back EMF to discharge the caps at such speed?:xeye:

You surely must have a very low impedance load connected such as your speakers shunting the whole circuit?
I'm no solid state expert (assuming this is what you're talking about) but I don't see that happening in tube circuit with a choke in series with the PSU B+.
I am as curious as you are here.

Cheers, ;)