5E3 Tweed Deluxe distorting problem

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#3
Some clear detailed pictures would most certainly help.

There are a number of places that could be causing that particular sound.
Bad tube or tubes. bad solder joint. Bad mica cap on the tone pot. As mentioned above dirty or loose sockets.

Really sound more tube related to my ears.
 
#4
No useful answer can be given without troubleshooting.
You *need* to scope it.
Otherwise all answers possible will be some variety of "it must be some thingie inside that amp".

Just to do something, measure all plate voltages and compare them to normal ones in a 5E3 , or post them here.

Although I suspect a bad ground or layout problem, and a multimeter won't help you in that case.
 
#5
I've built tons of stuff, including guitar amps, and I still occasionally forget to solder one or two connections until there's smoke, hum or general explosions. Recheck all your wiring and solder joints first. then turn it on and measure B+ for each stage, and then all plate voltages with no input signal, which should be somewhere between 1/3 and 1/2 of the B+ for that stage. If that's all good, I'd take a second look at the output tranny. Is it loaded right? Is it's primary impedance appropriate for the tube driving it? Did you do a "star center" grounding scheme, with only one ground connection to the chassis? (This means using I/O jacks that don't connect the ground wire to the chassis). Is the circuit oscillating at some supersonic frequency (a scope will show this)?

You need to keep input circuitry and any high impedance circuit nodes as far from output wiring and power supply as is practical. Filament wiring should be single strand 18AWG, and twisted fairly tightly, so the electromagnetic hum field they emit will largely cancel itself out. Keep those wires against the chassis and away from any grid circuit wiring.

Here's a link to a similar amp that I built:
Bobs 5Watt tube guitar amp
 
#6
Wow. Thanks for the responses - given me a few things to check out over the weekend. A couple of things: 1). The amp has been running perfectly since I built it about ten years ago, so the problem is new (ie not a build problem). 2). I've changed all the tubes but problem still there.

I'll clean all tube socket contacts and check and resolder Normal-Channel-specific components then report back.

Thanks to everyone who's responded so far - greatly appreciated!

Andy
 
#8
If plate voltages are off, check grid DC voltages with no signal. The caps feeding the grids seem to go bad a lot. If that cap blew shorted, it would put WAY too much positive voltage on the grid it's feeding, which would cause that tube to have it's accelerator pushed to the floor, which will blow the tube if it's left running for very long. I'd try to get the voltage readings and turn it back off within a minute of when I think it's warmed up enough to take the readings. Less than a minute is better. An output tube running full boar can also burn out the output tranny.
 
#9
I inspected the mains plug yesterday. Both the earth wire and the neutral wire had come loose - still in their little holes but the screws that clamp down onto the wire were loose, and I mean really loose. Tightened them up and it SEEMS to have cured the problem (time will tell).
Interestingly, I had a similar sounding distortion about 5 years ago with a 100 watt Carlsbro TC amp. I switched it off and plugged in the spare amp, a Marshall 2104, and experienced the same distortion. So I plugged into a different power supply socket and the problem went away.
Can any of you gurus here explain why a mains supply problem might cause this distortion?
Thanks
Andy
 
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