Problem with my amp...crackles and foghorns!!

[spkirby]

Hi,

one of my amps fell over in the trunk/boot of my car recently due to some hard braking I had to do to avoid a badly place "road closed" sign...

Anyway since then when i use the amp for say 15-20 minutes at pretty high volume (band rehearsal levels) I get some occasional loud crackles (similar to a bad cable kind of crackle!) and then after a few more minutes the amp just starts blasting out a sound like a foghorn...and continues to do so even with the volume on the amp set to zero...

I can switch off, then switch on and its fine for a few more minutes until the crackles then foghorn/feedback effect reappear...

Could it be a damaged tube/valve or does it sound like something more serious...

Cheers
Steve

 

[candid_x]

If it's a tube amp, my guess is that one or more of the tubes were damaged.

 

[spkirby]

Yep its a tube (valve) amp...

 

[andynpeters]

It´s broken....take it to the menders.

Sorry if that sounds simplistic, but it seems you´re not an amp doctor, and trying to fix a valve amp yourself could be dangerous.

 

[spkirby]

Thanks for the direct reply Andy! At this stage I'm simply interested to know if anyone can diagnose the likely source of the problem or has experienced a similar issue in the past...

 

[ivanmihaljevic]

It could be one of the preamp tubes

 

[Larry]

A pre-amp tube broke in the tumble.

 

[Mick]

Thanks for the direct reply Andy! At this stage I'm simply interested to know if anyone can diagnose the likely source of the problem or has experienced a similar issue in the past...

Hi Spkirby, being a tube amp tech I can only advice you to take it to a pro.
It´s dangerous even when unplugged from the wall for hours.

What it could be:

1: failing tube where the grids make problems after they have fully warmed up and crackle when the amp chassis moves while playing

2: Solder joints came loose and become hearable after warming up and the circuit boards moves a little due to the heat of the tubes.

3: Besides from that it could be everything so don´t try it by yourself. If you have a tech you trust take it to him. Maximum it could be the tubes , minimum solder work.

Hope that helps a bit. What kind of amp is it? Just interesting me.

Mick

 

[DrKev]

2: Solder joints came loose and become hearable after warming up and the circuit boards moves a little due to the heat of the tubes.

This is definitely my first thought. The warm up period means something is definitely responding to heat, so a solder joint is the first suspect in my book. Components tend to work or not work, and not often in something in between. With the the foghorn fart noise, I'd start with the solder joints on the tube sockets. After that I'd look at the input/output jacks. After that, it's a tech job.

 

[greenwizard]

Had the same problem with a solid-state, except it foghorned all the time. I sent it in to the factory and they said it was a melted transistor. I don't know if that helps with a tube amp but good luck.

 

[Dodgeball]

I'm going with the following being most likely...

1: failing tube where the grids make problems after they have fully warmed up and crackle when the amp chassis moves while playing

Because of these little bits of info...

A) I know Steve and he usually uses Cornford Amps which are point-to-point wired and thus have no PCBs. But you guys weren't gonna know that.

B) I had similar problems with my Laney 50w (PCB) about 6 months ago. Turned out to be one of the power tubes.

Good luck fixing it Stevo, I got the number of a good amp tech in Didcot if you want me to txt it to you.

 

[spkirby]

Hey Dodge,

please let me have that number...

You guessed right, this is a problem with my Hurricane...although I played on it at a generous volume for an hour today and no probs whatsoever...weird. And it was sounding seriously good...

By the way, I was in the Guitar Gallery today and tried out a couple of amps on a couple of EBMM's...Petrucci on Rivera Quina.... both guitar and amp didnt do it for me...then an Albert SSS and Laneys 40th Anniversary Lionheart amp...very nice!!!

If money were no object....

Steve

 

[Spudmurphy]

If it was me I'd try swapping out the valves- if you know anybody with the same valves buy em a pint to bribe them and borrow them.

Yeah I know it's dangerous to poke inside but this won't hurt. Strictly the biasing may change slightly but you wont hurt it for just a short while.

good luck and let us know.
Shame you are not here in Cardiff- one of my mates builds valve amps from scratch and another has a business repairing all tube amps.

 

[candid_x]

If it was me I'd try swapping out the valves- if you know anybody with the same valves buy em a pint to bribe them and borrow them.

Yeah I know it's dangerous to poke inside but this won't hurt. Strictly the biasing may change slightly but you wont hurt it for just a short while.

good luck and let us know.
Shame you are not here in Cardiff- one of my mates builds valve amps from scratch and another has a business repairing all tube amps.

That's what I'd do too. Always should have spare valves anyway. I'd start with preamp tubes, from V1 on. Why pay tech fees if it turns out to be a simple preamp tube?

 

[fbecir]

one of my amps fell over in the trunk/boot of my car recently due to some hard braking I had to do to avoid a badly place "road closed" sign...

You were certainly driving on the wrong side of the road (the left one ...)

Did you try to remove the valves (tubes for the US) and to put them again in the amp ? Perhaps, one valve was slightly removed from the socket.
Did you check the color of the tubes when they are warm ? A dead valve will tend to have a blueish color.
Hope that helps