Loud ac buzz with no input, help

[danielNoble]

Hello i have a 1985 JCM 800 orignal 2205 100 watt head)

the amp is fully stock

with the volume down on the amp and no input, theres a very loud AC buzz coming out of the speakers, when i turn reverb down it isnt as bad but still hearable and annoying, is it something to do with the power supply?

when guitar is plugged in, the noise from the guitar drouds the buzzing (when im playing) but when im playing on clean channel or low distortion.. the AC buzz is still audible

is this a fault? or is it normal? as i payed alot of money and it still under warranty (even though its 1985 )

any help will be much appreciated

 

[stax]

It sounds like 60hz cycle loop, meaning you've got a ground problem. If it isn't the amp (should be an easy fix) then it's where your setting up and playing your amp.

 

[janarn]

2205 = 50w
2210 = 100w
Does the warranty cover for the loss of 50W?

 

[danielNoble]

its a 2210 my bad,

in the UK, we use 240V

and a 50hz cycle AC

with nothing connected to the amplifier at all except the speaker, the AC is not being picked up from any of the inputs from the amplifier, could it be the smoothing capacitors in the power supply in the amplifier than have dried up after 23 years? and possibly need replacing?

 

[danielNoble]

anybody got any ideas?

 

[danielNoble]

bump

 

[Rareenergy]

did you make sure that you didnt have the head sitting on any wires or have any wires laying on each other? sometimes that does it

 

[RiverRatt]

could it be the smoothing capacitors in the power supply in the amplifier than have dried up after 23 years? and possibly need replacing?

That's the first place I would look. The constant hum even at zero volume is a dead giveaway. Sometimes the caps will bulge or leak when they are spent, too. It's not an expensive repair and probably needs doing anyway on a 23-year-old amp. You can replace them yourself, however, when you hear people mention lethal voltages inside tube amps, your filter caps are where those voltages are stored. If you're not absolutely sure of what you're doing, take it to a professional.

 

[xn7]

daniel, im having the same issue with a stereo amp from mid/early 1980, over the past few days i've been suspecting bad smoothing caps.

just curious, was your problem the caps?

 

[xn7]

That's the first place I would look. The constant hum even at zero volume is a dead giveaway. Sometimes the caps will bulge or leak when they are spent, too. It's not an expensive repair and probably needs doing anyway on a 23-year-old amp. You can replace them yourself, however, when you hear people mention lethal voltages inside tube amps, your filter caps are where those voltages are stored. If you're not absolutely sure of what you're doing, take it to a professional.

good info lol. i haven 't decided if im going to tackle my cap replacement or take to a shop. and finding the correct caps is a huge task by itself.

 

[RiverRatt]

Here's a good place to start:

50+50uF 500V 35x75mm Schellemontage TAD TubeAmpDoctor