How do I measure voltages correctly on these filters? This is for a twin reverb, blackface and I have the schematic for reference voltages. Is it one lead to ground, the other at B+1 for example, and set to DC? Should the stay be on or off when measuring? Observing all safety protocols of course. Thanks.
Yes, set to DC unless you are probing around the power transformer, before the rectifier (those voltages will be listed in AC). All of the caps have a positive and negative side, but the negative is not always ground. Just clip your meter’s black lead to the chassis (I typically clip to a screw or through a screw hole), sit on one hand or put one hand in your pocket, and probe with your red lead at the appropriate place shown in the schematic. I think most Fender schematics show the voltage points with the amp in run, not standby, but there may be both listed. Identify the positive side of a cap from the indent or the negative side from the side label pointing to it: www.digikey.com/en/blog/identifying-capacitor-polarization
Noob question but for your cap discharge tool/wire with the resistors soldered to it, what value resistors are you using? Also, I notice in a lot of videos, guys are using the old boxy wirewound type of resistors, but it looks like you’re using the metal film resistors? Can’t really tell under the heat shrink. Does it matter what type or material resistor you’re using? Thanks in adcance
It’s been many years since I made it, so I don’t 100% remember the resistance values, but I’m pretty sure they are 10K each for a total of 20K. They are definitely 5W metal oxide. Wire wound might be simpler to find in high watt values. I used two only because I didn’t have higher resistance value resistors on hand.
How do I measure voltages correctly on these filters? This is for a twin reverb, blackface and I have the schematic for reference voltages. Is it one lead to ground, the other at B+1 for example, and set to DC? Should the stay be on or off when measuring? Observing all safety protocols of course. Thanks.
Yes, set to DC unless you are probing around the power transformer, before the rectifier (those voltages will be listed in AC). All of the caps have a positive and negative side, but the negative is not always ground. Just clip your meter’s black lead to the chassis (I typically clip to a screw or through a screw hole), sit on one hand or put one hand in your pocket, and probe with your red lead at the appropriate place shown in the schematic. I think most Fender schematics show the voltage points with the amp in run, not standby, but there may be both listed. Identify the positive side of a cap from the indent or the negative side from the side label pointing to it: www.digikey.com/en/blog/identifying-capacitor-polarization
You're the best - thanks so much! @@hacksguitarhobby
Noob question but for your cap discharge tool/wire with the resistors soldered to it, what value resistors are you using? Also, I notice in a lot of videos, guys are using the old boxy wirewound type of resistors, but it looks like you’re using the metal film resistors? Can’t really tell under the heat shrink. Does it matter what type or material resistor you’re using? Thanks in adcance
It’s been many years since I made it, so I don’t 100% remember the resistance values, but I’m pretty sure they are 10K each for a total of 20K. They are definitely 5W metal oxide. Wire wound might be simpler to find in high watt values. I used two only because I didn’t have higher resistance value resistors on hand.
@@hacksguitarhobby Awesome, thank you so much for your reply!
How much does this cost to have done at a shop?
Not sure, I've always just done it myself.
@@hacksguitarhobby where do you order the parts from? I have a Randall 200watt G2 that started the 120hrz humming.
@@NordicRick usually tubedepot.com but I shop around some.