Amplifier Problems - Help!

[Ducatista47]

I have been beset lately with noises, and I suspect capacitors. Tubes may be another possibility. Line surges are somewhat unlikely but not impossible, as I have a Square D whole house unit upstream of the individual protectors the plugs go into. One of these could be bad. My signal path is so complex I need to narrow this down a little and any help is appreciated. The noises I describe are channel specific, but different channels!

The sounds are mostly cracks and pops, very similar to vinyl noises but much sharper and louder (nice definition, the 4345's reproduce them with unfortunately terrific fidelity. Go JBL!) There are some thumps, too. These all come and go. These are in the right channel.

Another class of sounds was so horrible and destructive sounding that I pulled the likely amp out of the path. These beauties were hissing building from low level to a really loud "sssssss" and ending with a very loud BANG!. Then normal operation until the next incident. So bad I feared damage to the speaker, but I got lucky. This may have been a 6260 as I haven't heard it since switching out the amp; so no tubes there. Still, I could not tell if it was on some or all transducers, so the 5235 is suspect too. This was a left channel problem.

I am switching components like mad to isolate the source, but I would still love to know what exactly to look for when I have the culprit component in hand. Jolida JD100 CD player (tube output), some non-electronic source switching, 5235 xover, 6290 low and Grommes PHI-26 (SET) high. All to biamped 4345's with stock networks, which I also suspect for no particular reason.

I am of course going to look for any visible arcs, but this takes time and I'm not there yet. Sparks make great signal sources, I've heard them elsewhere.

Thanks, Clark in Peoria

[Hamilton]

Hey Clark, I can only speak for tube guitar amps, but other than capacitors making loud pops I have also run into bad plate resistors. Also loose sleeves in the tube sockets that need re-crimping/cleaning are a prime suspect.

I start pulling tubes one at a time beginning with the input side until the noise disappears, this will hopefully indicator a suspicious area to start the interrogation.

[Ducatista47]

These tubes are all new or in the prime of lifespan, but I will pull them and have them tested today. Hope I don't have to track down all those possible solid state components. Ever seen the inside of a 5235? Blue caps everywhere. Good lord, and that is the simplest piece in the system. Plate resistors, here come the schematics...

What makes this really difficult is the highly intermittent nature of the problem.

I should ask Zilch about his vast 6260 knowledge.

Thanks, Clark

[GordonW]

I've had a 6260 exhibit similar behaviour. In fact, my 6260 got an extensive rebuild, due to "woofer walk", pops and crackles, and other transient no-nos. Turned out to be fried resistors and bad caps, the usual suspects.

For whatever reason, 6260s seem to "cook" some of their resistors and caps, if left on long periods of time over a long term. Once they're replaced, everything should be fine...

Regards,
Gordon.

[Ken Pachkowsky]

I ran into a similar problem yesterday on my brothers new system. All the drivers were snapping and popping, sounding like they were blown. It was the fact they all sounded blown that convinced me the problem lay elsewhere.

The problem was the balanced input circuit on the Perreaux SM6. I tried three sets of xlr cables with the same results. Switching to single ended RCA's solved the problem. Obviously there is a problem with the balanced input circuit.

As many here have taught me, strip the system down to its simplest form and isolate the problem.

Good Luck.

Ken

[Ducatista47]

Well, let's see...

First, you guys are like having a whole bunch of fairy godmothers to help a guy out of a jam. Thank you all so much!

Secondly, while I hate to see anything go wrong for anyone, misery must love company because I don't feel so picked on by fate anymore. I'm not the only one with gear that usually works wonderfully but craps all over me when it doesn't.

Thirdly, I see I am not the only victim of a signal path inspired by the Gordian Knot. This hi-fi quest lacks the virtue of simplicity sometimes.

Lastly, my audio shop is closed for the holiday weekend so the tube testing will have to wait. When I find out what ails my rig, I'll be sure to share the prognosis. Feel free to start a pool or something.

Keep the wisdom rolling in, I'll bet this topic has a wider interest than just my personal need. We newer fellows haven't faced the problems you veterans take for granted.

You are a great bunch for sure.

Clark

[Hamilton]

Secondly, while I hate to see anything go wrong for anyone, misery must love company because I don't feel so picked on by fate anymore.

You're not alone, I've been pulling my hair out all day on a '78 Marshall....but I think I found something...I think.

[Ducatista47]

You're not alone, I've been pulling my hair out all day on a '78 Marshall....but I think I found something...I think.

Wow, lots of pretty colors. The inside of my late 70's Mesa Boogie is dark, crowded and dank by comparison. Two meters, I'm impressed.

Good Luck Yourself, Clark

[toddalin]

Kind of sounds like what my subwoofer amp has been doing. In my case, it's the protection relay that keeps tripping back and forth making pops and clicks.

[Zilch]

Check the +/- 15V supplies in the 6260 on the o'scope or measure AC ripple on them. More than 10 mV ripple, replace the 10 uF electrolytic caps on the output of the 15V regulators (7815, 7915), which are cooking nicely right next to them there.

Like Todd, I suspect the protection circuitry, which runs off them.

Got my replacements at Radio Shack.