Amp Tech Thread / Ask a tech Q

[Pissy]

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]

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

[mortlock]

No obvious breaker to reset.

[RAGER]

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]

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]

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]

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]

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]

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]

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.