getting ready to make my first amp mods

[brownerthanu]

hey everyone,

i just purchased a kalamzoo reverb 12 that has a pretty nasty hum, regardless of the knob settings. i'm going to attempt a few of the mods found on this site, possibly including changing the caps. i have a few questions first. mostly safety stuff.

• where should i go to get or make a proper wire for discharging the caps?
• once i have it, what is a suitable ground to attach it to?
• in what order should i attach the ends, and how should i handle the wire?
• i noticed that the power supply caps have already been replaced. is there a way to test if they have gone bad again?
• is there any words of wisdom that i should know?

thanks for any help. i'm looking forward to learning more about guitar amps!

-reid

[stokes]

To discharge the caps,I have a 1k/3watt resistor wired between 2 alligator clips,but you could use any value resistor or even a straight wire,but a straight wire is going to give you a loud pop and could "weld" the connection at the cap or ground,better to use a resistor to "slow down" the discharge.Any ground is okay for this procedure,I usually just use any convenient spot on the chassis.Any order is okay,I generally connect the ground first and then the + end of one of the caps.When I have an amp with caps of an unknown age,I like to change them just so I know for sure their condition.There are many people who feel otherwise,but I like to be safe than sorry.Caps that test okay but are old can fail without warning and cause a lot of headaches,I would recomend changing them.An easy hum reduction method with a cathode biased amp is to just connect your heater CT or if it has the artificial CT that uses 2x 100 ohm resistors connect them to the cathode of the power tube,this effectively raises your CT enough above ground without having to make a voltage divider.Always be aware of where your high voltage is present in the amp.Try to keep one hand in your pocket when poking around in a "live" chassis,this will help keep you from touching a "hot" component and ground at the same time.Always assume there are high volts present,even if you have discharged the caps and everything seems to be "safe".I see this is your first post here,there are a lot of helpful people here,so dont hesitate to ask if you arent sure about something,better to ask what you might think is a dumb question than to learn the hard way and possibly hurt yourself or worse.The voltages in an amp,even when it is unplugged,can be fatal.This is,IMO,one of the best sites to learn about tube amps,a lot of helpful and experienced people here.

[brownerthanu]

awesome. thanks for the info! this is really helpful.