Forming filter caps
Posted: Sun Nov 12, 2006 5:24 pm
Forming filter caps...
... isn't also a bad things for new caps and enhances their physically parameters, also when they've been (quick-) formed at the manufacturer.
But for new caps, which have been stocked on the shelf for more than 5 years it's obligation!
I'm describing the steps valid for a 100W Marshall, with the 45W or 50W models you can share some of this steps:
- pull out the power tubes and the preamp tubes
- disconnect the yello wire going from the PT between the first two filter caps, temporarily tape the unsoldered end for safety (100W only)
- unsolder each one lead of of the both 56K bleeder resistors across the both screen's filter caps and tape it temporarily for safety (100W only)
- disconnect the red wire from the rectifier diodes (the rectifier tube) to the first filter cap and swap in temporarily a 100K/1W resistor
Now fire the amp up completely (power & standby to 'on') and measure the voltage drop across the 100K resistor you've swapped in!
You'll notice, that first you'll have a voltage drop of about 200V, which within 15-30 seconds reduces itself to about 30-40V - then further on it is dropping slowly.
If so, all's ok and you can switch off your meter and do your other things, because now the caps require 4-24 hours time to form, depending on the cap's quality and the cap's age.
Only insure, that nobody else could get in contact with your 'open' amp - way the best is, to lock the room, where the amp is sitting and keep the key in your pocket. It's danger to the life for unskilled people!!!
From time to time you can check the process of the voltage drop - and as soon as the voltage drop across the 100K is less than 5V (five volts), your caps are formed.
Switch off the amp - and before you remove the swapped in 100K resistor, implicitly bleed the caps by connecting pin #1 of V1 with an alligator clip to ground for at least 2-3 minutes!
Now reset the temporarily tweaks and put in all the tubes again - you've done Fire up the amp and enjoy its (valorized) sound
Larry
BTW: Also when an amp hasn't been in use for longer than six months, you should form the caps, before you fire up this amp again! If not, the longevity of the installed caps might be significantly diminished!
... isn't also a bad things for new caps and enhances their physically parameters, also when they've been (quick-) formed at the manufacturer.
But for new caps, which have been stocked on the shelf for more than 5 years it's obligation!
I'm describing the steps valid for a 100W Marshall, with the 45W or 50W models you can share some of this steps:
- pull out the power tubes and the preamp tubes
- disconnect the yello wire going from the PT between the first two filter caps, temporarily tape the unsoldered end for safety (100W only)
- unsolder each one lead of of the both 56K bleeder resistors across the both screen's filter caps and tape it temporarily for safety (100W only)
- disconnect the red wire from the rectifier diodes (the rectifier tube) to the first filter cap and swap in temporarily a 100K/1W resistor
Now fire the amp up completely (power & standby to 'on') and measure the voltage drop across the 100K resistor you've swapped in!
You'll notice, that first you'll have a voltage drop of about 200V, which within 15-30 seconds reduces itself to about 30-40V - then further on it is dropping slowly.
If so, all's ok and you can switch off your meter and do your other things, because now the caps require 4-24 hours time to form, depending on the cap's quality and the cap's age.
Only insure, that nobody else could get in contact with your 'open' amp - way the best is, to lock the room, where the amp is sitting and keep the key in your pocket. It's danger to the life for unskilled people!!!
From time to time you can check the process of the voltage drop - and as soon as the voltage drop across the 100K is less than 5V (five volts), your caps are formed.
Switch off the amp - and before you remove the swapped in 100K resistor, implicitly bleed the caps by connecting pin #1 of V1 with an alligator clip to ground for at least 2-3 minutes!
Now reset the temporarily tweaks and put in all the tubes again - you've done Fire up the amp and enjoy its (valorized) sound
Larry
BTW: Also when an amp hasn't been in use for longer than six months, you should form the caps, before you fire up this amp again! If not, the longevity of the installed caps might be significantly diminished!