Marshall 50w Making Crackle Noise at High Volumes

[stonecutter54]

I have an early 70's 50w Marshall that obviously has a problem and I'm trying to do some troubleshooting before I take it back to the amp tech.

When I crank the amp up to 8 or more on Vol1 and play low notes on the E-string using my neck pickup, I get a very distinct electrical, crackling sound. It sounds fine with the volume up to 6-7ish though.
The amp is not in the same room as the speaker, so vibrational effects should not be at play here.

Background:
A few weeks ago, I had a problem with the amp. I was playing it into a 4x12 and all of a sudden the signal totally died. I stopped playing immediately and shut her down.
Long story short.....The original speaker cable's jack housing became unscrewed (WTF?!) and it looked like the metal housing was touching the jack's terminals and that caused the signal to short out. I screwed the housing back on and the cable worked fine (I taped it down this time).

I went back to normal and then a couple weeks later when cranking up, I noticed the crackling sound. I had forgotten about the speaker short, so I did the normal tube swap and cleaning - still crackling. I decided to take it to the local amp tech. They replaced the resistor on V2's tube socket and said all was good. I even played the amp in the shop and there was no crackle!
I get it home and crank it up....CRACKLE!!

I will be taking the amp back to the shop tomorrow, but last night I went through the amp and touched up some of the solder joints related to electrolytic cap replacements...no luck.
Except for electrolytic caps, the amp is ALL original.

Did I damage the OT and therefore, ruin the amp? Is this behavior associated with a blown OT?
What other parts would be effected by a loss of speaker connection? The amp still sounds great, but cranked up to 8 you get the crackle on the low notes. Again, I tried different tubes and it still crackles.

Any help would be greatly appreciated. Thanks!

[beaulieu]

OT is prob fine. Anytime I have a problem it always ends up something simple easy...usually. You can probe carefully with a chopstick with the amp on and tap around till u find the problem. Usually works for me .Prob a cold solder joint or loose wire. Also stare at the parts inside for a while and you might see something suspect. Mark

[Lefty Lou]

Don't turn the volume up to 8. Speaking of 8, did you turn the amp up to 8 in the repair shop with a dummy load connected in order to more accurately replicate your problem? Recommendation, start first by getting a new high quality speaker cabinet cable.

[stonecutter54]

Thanks for the replies guys!

I'm going back to the shop tomorrow.

--I probed last night with a chop stick and one of the red caps was a little noisy - I will bring that up with the tech.

--When I picked up the amp, we cranked it up into a 4x12 speaker cabinet with a guitar and there was no crackle noise.
--I tried a shorter speaker cable and the crackle was still there. I believe its a little better quality cable, but nothing super high-end.

Here's a clip I made today:
First section: 50watt with the original tubes - Vol1 on 8
Second section: 50watt with totally different tubes throughout - Vol1 on 8
Third section: 100watt marshall with its own tubes - Vol1 on 8

I hear a distinct static/crackle sound with the First section. Not sure if its all gone in section 2 or if that is just normal amp distortion, etc.
Let me know if I'm hearing just things.....

https://soundcloud.com/stonecutter54/50-watt-noise" onclick="window.open(this.href);return false;

[neikeel]

Ip resume that you have taken the amp out of the chassis, or at least whipped the back panel off to look at the output tubes whilst you cane it?
Do you get a crackle from the OT housing of the amp when you do this?
To me sounds like something dodgy in the power section, in order of probabilies (given your scenario):

Damaged output tube
Once partly desoldered screen grid resistor (seen it twice now on 70's Marshalls)
Partial short on the OT (probably secondary) but only when cranked.

Once you have ruled out the first two I suggest you try your amp through an 8ohm load and use the 8 ohm and then 4 ohm tap - see if it still crackles.................

Not sure why your tech thought V2 plate resistor would be doing this given the recent history?

[Lefty Lou]

Thanks for the replies guys!

I'm going back to the shop tomorrow.

--I probed last night with a chop stick and one of the red caps was a little noisy - I will bring that up with the tech.

--When I picked up the amp, we cranked it up into a 4x12 speaker cabinet with a guitar and there was no crackle noise.
--I tried a shorter speaker cable and the crackle was still there. I believe its a little better quality cable, but nothing super high-end.

Did you try the shorter speaker cable at the amp shop after you had just checked the volume at 8 and found no noise? Your two statements above conflict. I checked the amp out at volume at the amp repair shop and no crackle noise BUT when I tried a shorter speaker cable the crackle was still there?

Here's a clip I made today:
First section: 50watt with the original tubes - Vol1 on 8
Second section: 50watt with totally different tubes throughout - Vol1 on 8
Third section: 100watt marshall with its own tubes - Vol1 on 8

I hear a distinct static/crackle sound with the First section. Not sure if its all gone in section 2 or if that is just normal amp distortion, etc.
Let me know if I'm hearing just things.....

https://soundcloud.com/stonecutter54/50-watt-noise" onclick="window.open(this.href);return false;

[Strat78]

By chance could it be that you are clipping your recording device. I had the same problem but luckily discovered the problem before tearing into the amp.
http://soundclick.com/share.cfm?id=11209240" onclick="window.open(this.href);return false;

[stonecutter54]

Did you try the shorter speaker cable at the amp shop after you had just checked the volume at 8 and found no noise? Your two statements above conflict. I checked the amp out at volume at the amp repair shop and no crackle noise BUT when I tried a shorter speaker cable the crackle was still there?

Sorry - I tried it at the amp shop through their 4x12 and found no noise.
Later in the week at home, I tried it with 2 different speaker cables (one long and one short) and the crackle was there for both tests.

[Lefty Lou]

Did you try the shorter speaker cable at the amp shop after you had just checked the volume at 8 and found no noise? Your two statements above conflict. I checked the amp out at volume at the amp repair shop and no crackle noise BUT when I tried a shorter speaker cable the crackle was still there?

Sorry - I tried it at the amp shop through their 4x12 and found no noise.
Later in the week at home, I tried it with 2 different speaker cables (one long and one short) and the crackle was there for both tests.

So the speaker cable at the shop was one of the "2 different speaker cables (one long and one short) and the crackle was NOT there for both tests?"

[stonecutter54]

So the speaker cable at the shop was one of the "2 different speaker cables (one long and one short) and the crackle was NOT there for both tests?"

No. Let me re-state the sequence......
When I picked up the amp, I tested the amp at the shop through their speaker cable (no idea what it was) and their 4x12 cabinet (some more recent looking Marshall model) and there was no crackle, so I took the amp home.

Later in the week, at home, I cranked the amp up to 8 and played it through my 4x12 cabinet- I still heard the crackle noise. After hearing the crackle again, I did two separate tests to see if it was a bad speaker cable that was causing the issue. Each test used a different speaker cable; the first test used a 50 foot long cable and the second test used a 10 foot long cable. On both tests, I still heard the crackling noise.

Sorry for any confusion.

[stonecutter54]

By chance could it be that you are clipping your recording device. I had the same problem but luckily discovered the problem before tearing into the amp.
http://soundclick.com/share.cfm?id=11209240" onclick="window.open(this.href);return false;

I recorded the amp at various mic levels (low to high) and the crackle sound was still there. I wish it was just digital clipping...

[Tazin]

I ran into a kinda similar problem a while back. The amp had a sporadic cracking noise predominate at high volume. Turned out to be a lightly corroded mains fuse.

[neikeel]

I ran into a kinda similar problem a while back. The amp had a sporadic cracking noise predominate at high volume. Turned out to be a lightly corroded mains fuse.

That would be nice!
Other things along those lines are that the output and mains selectors are tight in their sockets (window type?) and the pins are clean.
we skipped over things that your tech should have done - clean out all the sockets, check for carbon track arcing on the output tube octals etc, etc.

[dukeamps]

When I got my 1975 JMP 100w sl, I also had this problem, after doing a bit of chop sticking, turns out it was the standby switch shorting out, I just replaced it & all is good,

[Lefty Lou]

So the speaker cable at the shop was one of the "2 different speaker cables (one long and one short) and the crackle was NOT there for both tests?"

No. Let me re-state the sequence......
When I picked up the amp, I tested the amp at the shop through their speaker cable (no idea what it was) and their 4x12 cabinet (some more recent looking Marshall model) and there was no crackle, so I took the amp home.

Later in the week, at home, I cranked the amp up to 8 and played it through my 4x12 cabinet- I still heard the crackle noise. After hearing the crackle again, I did two separate tests to see if it was a bad speaker cable that was causing the issue. Each test used a different speaker cable; the first test used a 50 foot long cable and the second test used a 10 foot long cable. On both tests, I still heard the crackling noise.

Sorry for any confusion.

SO, the common denominator is THEIR cabinet and THEIR cable resulting in no problems, And YOUR cabinet with YOUR cable(s) resulting in problems. I'd say you need to take a closer look at your CABINET.