sudden, weird noises from my fisher integrated

[madwing]

i've been listening for more than a month to my lovely little fisher integrated mono amp (chassis 50, p-p el84, 5y3, 12ax7, 6sc7), and it's been very well-behaved.

this morning, after a weekend and a day of not running it, i turned it on, plugged in my iphone and lit up pandora; this is a usual for me, and it's never caused me any problems except for the occasional static.

this morning, however i noticed two or three loud *pops* (as opposed to the paper-crinkling signal static) after about a half hour of listening, and then a bit later a high-pitched screech that sounded like a cross between a needle dragged across the grooves of a record and the sound tires make on asphalt when their brakes are locked up.

on the latter sound i immediately turned off the fisher, let it rest, then turned it back on. listened to half a song, and the loud *pops* came back a couple of times. i've turned it back off, for now.

tube going bad (which one?)? resistor or cap (coupling or power section)? or is that just a bad signal from the pandora stream?

thanks.

 

[Endspec]

We need a bit more info on the unit, Has it been re capped or is it all the factory parts in it? If it has not been gone through it will need a re cap and check the resistors at the minimum. Could also be a dirty tube socket causing some of the problems too.

 

[derekva]

Microphonic preamp-section tube perhaps causing oscillating feedback? Try lightly tapping on each preamp tube with a pencil eraser when you first turn on the amp and see if you hear noise. Not sure if a bad coupling cap would cause this sort of behavior or would just fry an output tube.

No red-plating on your tubes, I'm assuming...

-D

 

[audiodon]

Yeah,
I'd wiggle the tubes with the volume very low first. Second, try a different intput source. Other than that, I'm with Endspec. We need more input.

 

[madwing]

the coupling caps have been replaced by orange drops; the only 'lytics left are the cans on top, which haven't gotten hot in the least when i've run them.

no redplating.

listening to the ipod portion of my phone now. tapped the 12ax7 and 6sc7, and nothing changed (no noises heard through the speakers from the tapping).

the squeal, and the pops, were at much higher volumes than the song being played.

 

[diamondsouled]

When you said you: "lit up Pandora" I thought you were talking about a cigar at first

Could be any number of things that could be causing the intermittent noises. Learning to trouble shoot is mainly learning how to narrow down what could be causing the problem.

First try a different source.

Then if it is still symptomatic try lightly taping the tubes with a pencil eraser. If the problem is a microphonic tube it will be quite apparent. Changing out that tube will tell you definitively if that was the problem, sometimes.

Eliminating what could be causing the problem is the only way to find out what isn't causing the problem and eventually tracking down what is.

There are a lot of things which will cause the symptoms you referred to. Here's a partial list:

Cold/bad solder joint.

Bad interconnect.

Resistor failing.

Capacitor failing.

Tube failing or microphonic.

Signal source related.

Power source related ...

Cheers

Lar

 

[madwing]

ah, lar, you slay me. it's supposed to be something *simple*, damn it!

i've turned off all sources right now and it's just playing some very minor static...

i'll let it rest a bit, then turn it off so i can deoxit the sockets again.

how do i spot a cold/bad solder joint?

 

[dr*audio]

I have seen a dirty tube socket cause noises like this. If you can get it to do it again, wiggle each tube in it's socket and see if the nois goes away. If so you can clean the tube socket contacts (with the power off) with a wound guitar string. Use the thinnest gauge that will fit with a little resistance. Too tight and you'll loosen the contacts.

 

[archie2]

Those "lytics" cans on top, they are the original?

 

[diamondsouled]

ah, lar, you slay me. it's supposed to be something *simple*, damn it!

i've turned off all sources right now and it's just playing some very minor static...

i'll let it rest a bit, then turn it off so i can deoxit the sockets again.

how do i spot a cold/bad solder joint?

It is something simple it's only finding it that's isn't so simple. :yes:

Cleaning the tube sockets is a good place to start. Also it might be a good idea to tighten the tube sockets a little with a tiny screwdriver. This will often cure such problems.

Finding a cold solder joint can be easy, but then again.

Eliminate all the usual suspects first, tubes, tube sockets, connects, source, etc., before opening er up.

Some folks reflow all the solder joints as a matter of course, especially in kits. Makes for better connectivity and eliminates any cold solder joint issues.

I usually inspect all solder joints visually and then poke them with a chop stick when the amp is off to be sure they are soldered on tight. If you are comfortable working around live gear you can do the same with it powered up and plugged into speakers and any questionable solder joints will announce themselves very clearly when prodded. Be sure to use a prod that is non conductive though!!!

I would suspect something like a tube or a loose/dirty tube socket first though.

Cheers

Lar

 

[madwing]

simple: contact cleaner on the el84 pins, insert and remove a dozen or two times, and seat well. let heat up, and run for a while, and the odd noises haven't (finger's crossed) returned.

thanks for the advice!