Amp Tech Thread / Ask a tech Q

Pissy · September 13, 2021, 10:33:13 AM

Internal fuse would be my guess. No smoke right? If not that then something else with power delivery. Cracked solder joint or something.

Does it have a breaker like thing to reset? Pics?

mortlock · September 13, 2021, 11:27:12 AM

Not mine but this is the one i have. Internet pics.
No smoke, no pop, no nothing.

mortlock · September 13, 2021, 11:28:04 AM

No obvious breaker to reset.

RAGER · September 13, 2021, 12:52:54 PM

I would give everything the wiggle test. Wiggle cord at outlet when plugged in, wiggle power switch. If that doesn't show you anything then it's time to get the screw gun out and partially disassemble to do a visual. NOT PLUGGED IN. There is almost definitely a fuse near where the power comes in by the power transformer/power cable entry.

If you're not comfortable with that or even going further with the chopstick test with power on DANGEROUS then you gotta seek a tech.

Muffin Man · September 13, 2021, 01:45:30 PM

if you're concerned about your prostrate just wait till you start digging around inside an amplifier pretending to do your own tech work - things could really puff up quick. Nice piece of iron haging off the back of it though.

oh my
https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/35747-ampeg-b100r-power-transistors-saturating

mortlock · January 08, 2022, 10:32:11 PM

how would i convert that combo so it just functions as a speaker cab? how do you install a 1/4 in jack to the existing speaker?

i want to pull out the head and power the cab with a different head.

RAGER · January 09, 2022, 02:40:40 PM

It's very possible to salvage pretty much everything you need to do that from parts from the amp section. Mono input jack, screws, backing plate material and the speaker wires are probably long enough too. You just have to possess the know how and done soldering skills and the tools of course.

There's plenty of stuff online regarding how to wire a mono speaker jack. I'd come over and help but you got Covid probably. And you live 3,000 miles away.

mortlock · May 02, 2022, 07:58:09 PM

if you remove the tone pot from a fender p bass. how does the pickup naturally sound. is it treble side, bass side or in the middle? what determines that?

RAGER · May 02, 2022, 11:07:51 PM

Quote from: mortlock on May 02, 2022, 07:58:09 PM
if you remove the tone pot from a fender p bass. how does the pickup naturally sound. is it treble side, bass side or in the middle? what determines that?

Probably the value of the capacitor.

Pissy · May 03, 2022, 06:22:42 AM

So a resistor in parallel with a capacitor creates something called an RC circuit. An RC circuit has a unique property related to AC signals that allows passage of the signal through the capacitor from a specific frequency and beyond.

The values of both the capacitor and the resistor determine where in the frequency spectrum that point occurs. It's called resonance.

In a guitar, the signal from the pickup is full spectrum- basically- until it gets to the tone RC circuit. Since the resistor in that parallel RC circuit is a potentiometer, the frequency point changes based on where you twist the knob. With a tone pot, those upper frequencies are peeled away from the signal and allowed to pass through the RC "gate" to ground effectively removing them from the signal going to the volume pot, and ultimately the amp.

If you pull the tone pot and that cap out, it's much like turning the tone knob all the way up. But not 100% exactly because the presence of the components colors the sound a little, for better or worse.

Most all tone circuits on amps or guitars or even stereos for that matter use this same principle. Coloring the sound by being selective about what is removed, vs adding boost to any specific frequency range.

mortlock · May 11, 2024, 07:39:10 PM

question. on a peavey combo amp the ground prong on the plug snapped off flush. the amp still turns on when plugged in but im wondering what will happen if its used without the ground prong. im assuming its not safe??

Pissy · May 12, 2024, 11:59:18 AM

It's not technically safe, because if a high voltage component within the amp, say the main 110 from the wall, touches the chassis of the amp, it will energize the guitar and you. If the ground is there, all (or most all) of that current will get run straight to ground, tripping the breaker, blowing the fuse, getting really hot... something other than electrocuting the user.

Having said that so many houses i used to live in had two prong outlets, and anything that needed the ground lug got an adapter that is supposed to hook into the screw in the middle of the outlet, which I don't think many people do. It's never happened to me, but its feasible. Replace the cord or the plug on the end. They're cheap (replacement plugs) from HD or Lowes and easy to do with a screwdriver and an exacto knife to strip the wires.