Distorted pingy plexi?

[Natec]

Here is my 1959 JMP that now has a bad top end distortion. I hope it's not the kt77's I put in. In my vid I say all is dimed. ( not the lar/mar ppimv of course ) what do you think? Prolly tubes huh?

http://m.youtube.com/watch?v=wm4giG5Hn8E" onclick="window.open(this.href);return false;

[Lefty Lou]

Voice coil(s) (and/or) one or more filter caps. What is the total power handling of your cabinet? 100 watts, 120 watts? If you've got G12Ms or G12Hs rated at 25 and 30 watts respectively then you've got troubles. Some guys don't realize that with tube amps, rated power is exceeded easily. Some Marshall 1959 Super Leads are capable of putting out 160 watts or greater.

How old are your filter caps and electrolytics ? When was the last time you changed them?

[Natec]

Definitely not speakers. There is another amp sitting on top of this plexi that you can't see. It sounds fine. The plexi is not all that loud. The volume in the video is not enough to gig at.

[Natec]

If the filter caps were going bad wouldn't I get more 60hz noise? That's what they do right filter that?

[stef]

preamp tubes - have had the same problem - gone with the 12ax7 tube swap
Check the bias too

[Natec]

May have had a bad cable? I plugged in a humbucker and it now sounds dark?

[Lefty Lou]

If the filter caps were going bad wouldn't I get more 60hz noise? That's what they do right filter that?

1) Not necessarily. 2) Yes they "filter" AC, but again when was the last time you changed said filter caps, or any of your electrolytic caps ? Symptoms of decreased power supply filtering are hum, buzz, motorboating, loss of power, ghosting, and strange noises.

If preamp tubes are suspect, some will use the "chopstick" or "pencil eraser" method by turning up, and lightly tapping on a preamp tube to check for microphonics. You can do this prior to swapping out preamp tubes one at a time. If you do the swap, start with your (PI) phase inverter/driver preamp tube closest to your power tubes and move move left (looking at the back of the amp) towards your first gain stage preamp tube.

[Lefty Lou]

May have had a bad cable? I plugged in a humbucker and it now sounds dark?

Did you swap your guitar cable and experience little or no noise? One very simple thing that guys overlook (with some cheaper cables) is tightening the 1/4" jack at either end of the guitar cable.

[Natec]

I do get a bit of ring when tapping v1. It doesn't keep ringing but it's definitely more than the others. I will put in a new one and see what gives. I'm still amazed at how drastic the difference was between the ultra too bright strat too the way too dark humbucker? Something is weird? Tube it tomorrow, then I will check back.

[Lefty Lou]

??????????????????

[Doug H]

I can hear it when I tap V1, and not the others. I think that's normal cause it doesn't seem to change when I switch tubes around. Amp sounds great except for that scratchy problem.

Sounds to me like something is very very wrong, like a really bad tube socket or a 99% broken or loose wire.

[neikeel]

Ok I am puzzled, Doug H answers the question, not Natec

Sounds to me like duff tubes, as always drop in some different ones (pre and post) rebias the outputs and please come back with results.

[Doug H]

Sorry, I meant, I can hear v1 on my amp when I tap on it as well, at least more than the others, I think that's probably normal.

[Lefty Lou]

The jury is still out, and the fat lady hasn't sung just yet.