when small speakers fart out.

so. i recently acquired a 66 vibro champ. lovely. i put an 8" 4 ohm tone tubby ceramic in there. today i really opened her up for the first time at my studio. i cranked her past "8" and...when i really slammed down that open low "E" the amp would periodically make a LOUD rapid rattling/buzzing sound. is this the infamous 8" fart-out? or could it be that i didn't tighten the speaker down tight enough?

thanks.

Has that amp had a tune-up? A friend of mine has a '66 VC he bought in a junk shop for $20 and it was obviously sick. The bias resistor was way out-of-spec and signal caps were leaking DC. You couldn't give it much gas without it sounding really "blatty."

Has that amp had a tune-up? A friend of mine has a '66 VC he bought in a junk shop for $20 and it was obviously sick. The bias resistor was way out-of-spec and signal caps were leaking DC. You couldn't give it much gas without it sounding really "blatty."

just got her back from my tech, and he seems to be pretty good. any other ideas?

just got her back from my tech, and he seems to be pretty good. any other ideas?

What all did the tech do to the amp?

What all did the tech do to the amp?

the vibrato was really weak when i got it. he changed a couple caps that had drifted out of spec in that part of the circuit, and i believe he replaced one resistor that had apparently doubled in value over the last 40 years. he also changed it to a 3-prong cord. i should mention, when i put the speaker in, all i had were some flat nosed pliers to tighten it up with. i just found an (almost) right size wrench, and the screws tightened up like 3 turns more each. i can't crank the amp at home though to check it:cry:

I would vote for a loose speaker for now. Don't overtighten it though.

Generally, fart out is when you loose definition or loudness/power on really low notes. It could also brap out like you're talking about.

I'd ask the tech. Seems like he'd have check over the screws or tested the sound as part of a tuneup. So maybe he can tell you more definitively.

It's been a long time since I had my Vibro Champ, but what I recall is that at higher volumes, instead of reproducing mainly the fundamental of a low note, it sounded like it was reproducing just a bit of the fundamental and much more of the overtones/harmonics, as that was more in the ability of the transformer and speaker to handle when pushed.

the vibrato was really weak when i got it. he changed a couple caps that had drifted out of spec in that part of the circuit, and i believe he replaced one resistor that had apparently doubled in value over the last 40 years. he also changed it to a 3-prong cord. i should mention, when i put the speaker in, all i had were some flat nosed pliers to tighten it up with. i just found an (almost) right size wrench, and the screws tightened up like 3 turns more each. i can't crank the amp at home though to check it:cry:

Don't crank the nuts too tight. Just past finger tight is good. You want them to be screwed on solidly, but not so much so that it bends or warps the speakers frame.

The tech should have also replaced all of the electrolytic caps in the amp in that has not been done recently. Old leaky filter caps can cause farty washed out bass.

Back the Bass down from 8 and I bet ya the farting will most likely stop.

just cranked it again after tightening the nuts holding the speaker. still crackling after "8" on volume. rolling bass back helps a little, but only rolling the volume back under "7" fixes it. could this be a circuit issue?

just cranked it again after tightening the nuts holding the speaker. still crackling after "8" on volume. rolling bass back helps a little, but only rolling the volume back under "7" fixes it. could this be a circuit issue?

Well again, this could be an ancient, dying filter cap issue. Vintage filter caps may look cool, but they are like driving on vintage tires...it just doesn't work.

Past that, every vintage amp has its "sweet spot". When cranked up much past that spot, they tend to crap out.

It's a 4 - 6 watt amp right? Even in tip-top working order, and even with a killer speaker, the amp has its limitations.

Well again, this could be an ancient, dying filter cap issue. Vintage filter caps may look cool, but they are like driving on vintage tires...it just doesn't work.

Past that, every vintage amp has its "sweet spot". When cranked up much past that spot, they tend to crap out.

It's a 4 - 6 watt amp right? Even in tip-top working order, and even with a killer speaker, the amp has its limitations.

this is good info. thanks.

being as it has a bass control, i'm with tazzboy in that if you roll it down, you're gonna get less fart. in a jam situation, you won't miss those muddy lows at all -- in fact, they just suck power from the sweet part of the spectrum.

Yeah when play loud you don't need a lot bass, but when play quietly they you well need some bass.

Van guard,
When I got my SF Champ, I had a cap job done on it and put in a good speaker- you can't make it fart out on any setting ... dime every knob, doesn't matter, sounds great.
The way to test your amp to see if it's the speaker is: get a 4 ohm cabinet with a bigger speaker(s) and crank it into that. If the sound holds together, you know it was the 8" speaker, not the innards of the circuit. Make sure you use a good speaker that can stand the peak wattage of the Champ.
best wishes

so it turns out it is an elecrolitic cap. how many are in there? should i just have my tech replace all of them, or just the faulty one? what's going to give me the best result? i'm not a collector, so i want to do whatever will make the amp sound and function the best.

so it turns out it is an elecrolitic cap. how many are in there? should i just have my tech replace all of them, or just the faulty one? what's going to give me the best result? i'm not a collector, so i want to do whatever will make the amp sound and function the best.

If they are the originals, or replacements that are 10 years old or older, they should ALL be replaced.

If your car had four bald tires, and one of them blew, would you replace just the blown tire, or all four?

Your amp has one multi-section electrolytic filter cap with three 20uF sections, and three small cathode bypass electrolytics. Looks like two 25uF/25V and one 10uF/25V

http://www.ampwares.com/ffg/schem/champ_vibro_aa764_schem.gif

http://www.ampwares.com/ffg/schem/champ_vibro_aa764_layout.gif

I would replace all the elec caps. I can't think of any GOOD reason not to. Leave the cans attached and disconnected if you like how they look and care about originality. But function is king, so get some new caps in there!

And don't go all taste-testing crazy here. These electrolytic caps only do the job of taking the 60 cycle hum out of the rectified power. If the amp doesn't hum or sag, you're all good.

BTW, I'm rather surprised your tech didn't check these first. You can almsot count on them being weak on an old amp.

Best,
--Rob

Leave the can attached and disconnected if you like how they look and care about originality.

Why not replace the multi-section can with a new one? Antique Electronics/CE has just what he needs.

http://www.tubesandmore.com/cemirror/inv/C-EC20X3-525.GIF CAPACITOR, ELECTROLYTIC, 20/20/20 µF @ 525 VDC

C-EC20X3-525

Made in the USA on Mallory's original machinery.

* 3 sections - all 20 µF @ 525 VDC
* -10%, +50% tolerance
* 85° temperature rating
* 1-3/8" diameter x 3" tall

http://www.tubesandmore.com/


I too find it curious that his tech didn't replace them all the first time.

i'm ordering one of those cap cans. i feel like a sucker for buying an all original 60's amp. it seems "all original" really just means, "unless this is going behind glass, you get to remove half those original parts and pay for new ones!":lol: :roll:

i'm ordering one of those cap cans. i feel like a sucker for buying an all original 60's amp. it seems "all original" really just means, "unless this is going behind glass, you get to remove half those original parts and pay for new ones!":lol: :roll:

You really should have your tech order the parts needed, because you need more than just that multi-can.

You're looking at this the wrong way.

Think of tubes and electrolytic caps like tires and batteries with cars. Are you going to dis a 57 Chevy because it needs news tires and a battery to make it drivable? I hope not!

You really should have your tech order the parts needed, because you need more than just that multi-can.

You're looking at this the wrong way.

Think of tubes and electrolytic caps like tires and batteries with cars. Are you going to dis a 57 Chevy because it needs news tires and a battery to make it drivable? I hope not!

ha. you're right. i actually just gave my tech the link to the cap can. he already fixed the trem and replaced some other resistors and stuff in there. i'm sure he'll just get whatever he needs in addition to that. he said the reason he didn't change the electrolitic caps before was because they were all close to spec. he also said he tried not to change anything that wasn't absolutely necessary because it looks like a museum piece it's so clean and original, and he assumed i wanted to keep it stock above all other considerations. i set him straight. i'm a player first.

Glad you set him straight. Never could see putting any useful piece of equipment under glass.