Amp Falls From Height of Six Feet and Survives (sort of)!

[AJD]

Okay, first, I am an idiot. For reasons that I will not go into my tube amp fell from a height of about six feet. Now when I turn it on, while it still "works", it does have a problem. The problem is that the notes played sound a bit out of tune. I do not know if oscillation is the correct term to use, but it is the first descriptor that came to mind. What is also odd is that the higher the note, the greater the apparent "out of tune-ness". When playing the low E string, the amp sounds ok. When playing the A string I think I might hear some out of tune-ness. When playing the D string I hear a faint out of tune-ness. I hear a more present out of tune-ness when playing the G string. The out of tune-ness gets progressively worse with the B and high E strings.
The amp in question is one that I built that is basically a Princeton clone or a Two-Stroke. It is split into a head and cabinet formation (both took the same fall). Prior to the fall it sounded great. I can post a schematic if anyone thinks that it might be of help. I changed all of the tubes (including the rectifier) with known good ones. Twice. Problem still persists. Could it possibly be the filter caps? I really don't know where to begin or how to go about diagnosing the problem. Any help would be greatly appreciated. Thanks in advance.

[TUBEDUDE]

First i'd plug into another speaker cabinet to verify the source of the problem isn't the speaker.

[Gibsonman63]

I have heard that filter caps could do that, but mainly on the lower notes because they take more power to produce.

The speaker is an easy and logical check.

If you want to shotgun it, then refllow all of your solder joints. If it fixes the problem, chalk it up to a broken solder joint and get back to playing.

[Structo]

My first thought is a tube got damaged and as Gibsonman63 suggested it may be a filter cap that was damaged.

But first check out the speaker. You may have shifted the magnet.

Divide and conquer in your troubleshooting.
Check out the tubes one by one then if it still does it you may have to start replacing caps.

[Prairie Dawg]

This is a true story.

The first amp I ever did a serious overhaul on was a Fender Quad Reverb. I got it home and started stripping it out and I noticed the cabinet was sort of a parallelogram, the baffle board was broken in numerous places, and the chassis had about a 15 degree axial twist. So I call the onwer and say "Was this amp in a car accident?" He says "Oh, yeah. I bought that amp in a bar for fifty bucks. I was playing a gig in a second floor hall and it fell down a flight of stairs. It still worked so I finished my gig and forgot about it. That was about ten years ago." So I jacked the cabinet back into shape with clamps and wood glue, reinforced the baffle with corner braces from menard's, clamped the chassis down to a railroad tie and reefed it back more or less true and as far as I know it's still running even though the owner passed on.

What current day amp do you know of that could survive that?

[Structo]

Meh, Alexander Dumble throws his amps from moving vehicles to test their durability.

[Firestorm]

It sort of sounds like a cap problem. Check all the filter cap connections, not just solder joints but the leads themselves.

[AJD]

Thank you all for the advice. Now for another embarrassing admission; the amp sounded so good that eventually I sold all my other amps and cabs and now I don't have another guitar speaker laying about! I did plug headphones into the amp output and the problem remained so I figured the problem was in the amp itself. Later tonight I will source an actual speaker and give it another try. There are only a few filter caps in the thing and I have spares on hand so I will give that a go if the speaker check fails.

[plexitone]

Ouch! If you've ruled out the obvious (speaker, tubes...)

Your "out of tune" description sounds like ghosting. If it's worse when loud (overdriven), it might be that. Check the filter cap ground connections especially.

[Zippy]

Given the mass of a filter cap, it is a reasonable part to expect to fail in a fall like that. Maybe gooping the filter caps (or tying them down) is not such a bad idea after all. Either that, or don't leave your amps on top of the minivan. That's not what you did, is it?

[M Fowler]

Or if you ever play on a platform on top of a school bus at We Fest in Detroit Lakes, MN like I have they could fall a lot higher then that!

Hell of a view from up there though

Probably bad tubes and bad cap. Old caps can sound out of tune but a broken cap I would think would just plain not work.

Mark

[selloutrr]

Tighten all your grounds! nuts, bolts, solder points.

most dead caps (blow up / fizz and stop holding energy) make the amp hum. Not shift notes. Tubes / tube sockets cold solder points broken wires - making the path or least resistance to ground while still conducting correctly would cause a shift in tone or frequency. Capacitors if they old and slowly dying.. i.e. 100MFD now only operating at 10MFD may cause a shift but I would suspect it to be most noticable in the bass response. If the electrolytic caps are over 10 years it's probably best to just replace them.

If you can visually see damage to the caps replace them. It is possible in the fall the cap was damaged the energy had to go someplace. New caps have a vent hole so they no longer explode. they just fizz out of the hole.

Another way you can test if it's filter cap related... What are your voltages? how different are they from when you built the amp?

If you safely know how to work on amplifiers you can do a basic good bad test on any electrolytic capacitor with a volt meter.

after you tight grounds
touch up all your solder points It's quicker then trying to tack down the cold solder point if nothing is visually not connected.
test the entire amp for continuity refering to the schematic and or layout for correct location.
tighten tube sockets - retension pins
test - if the issue is still present
Do the cap job

amp will be good to go!

should take you less then an hour.

Make sure you discharge the filter caps first!
If you aren't comfortable working on the amp. I'm in palm springs.

[AJD]

Thanks to everyone for all of the suggestions. I really do appreciate all of the feedback. Caps and all other components are only two years old and visually everything looks fine on the inside (no leaky caps, broken joints, etc....). Time to get out the voltmeter,etc... and see what is going on in there.I'm going to put the patient on the bench now and hope to be back with an update in a bit.
The truth about the spill that the amp took is not nearly as interesting as falling down a flight of stairs, off the top of a minivan or from the roof of a bus, but is far more embarrassing. I live in a modern house with finished concrete floors. The other day I was mopping the floor and I had to move the amp out of the way for a minute or two. Against my better judgement I lifted the entire amp stack and stood it on the bed, cause hey, it would only be there for a minute right? Well a minute was about 30 seconds longer than that amp was willing to remain on the bed, cause it came toppling down behind me with a gruesome crashing sound. I am still kicking myself. Hard.

[Andy Le Blanc]

if you know which side it landed on

drop from 2 feet 3 times on the other side

there's easier ways to tune your guitar...

[Gibsonman63]

if you know which side it landed on

drop from 2 feet 3 times on the other side

there's easier ways to tune your guitar...

It would be much easier than rolling an amplifier upstairs.