One dead tube = silence?

[fweijers]

I have a DSL100, and today I got no sound from the amp.
So I opened up the back side, and found out that one power tube is not glowing.

It's the first power tube from the left.
(looking in the amp from the back-side, on the left are the pre-amp tubes and on the right the 4 power tubes)

Can the sound be killed totally when one tube (particularly this one) is dead?

 

[RickyLee]

Yes . . . If it took a fuse out or another component or worse.

Did you check the HT fuse?

 

[fweijers]

No, because the other tubes are glowing I thought the fuses should be ok ...
However, this may be a bad assumption. Where is the HT fuse located?

 

[hbach]

If the HT fuse is blown the tubes will still glow because the heaters are on a separate circuit. The HT fuse blown is similar to the amp en standby.

 

[fweijers]

Ok, thanks! Will check and replace the HT fuse.

Replacing only the dead tube will result in a non-matched tube amp ... if this is a good idea or not will be a whole other forum thread, I suppose ;-)
(I will bias them, though)

 

[RickyLee]

Be careful as to not put too hot (current) of one in there as a replacement.

 

[john rich]

fweijers,

I believe the power tube in questions is V5.
Check the fuses, especially F1, that's the fuse that leads directly to the heater on the V5 tube, the schematics show a 6.3A fuse there.

Best change the tube(s) as well.


NOTE!!!!
Amplifiers can be dangerous if you don't know the basic safety practices!
If your not sure what your doing, DON'T DO IT! You can seriously injure yourself or get yourself killed.
Just look what happened to this guy...
[ame=http://www.youtube.com/watch?v=V9GR9H3qUE4]Guitar Amp Electrocution - Ouch!.wmv - YouTube[/ame]

 

[Ken]

Buy 4 new power tubes and have the amp rebiased. Keep the other 3 as spares. Hopefully that's all you need to do.

Ken

 

[duffhuff]

Do the pre-amp tubes heaters all light up as well? 'cos it looks like that fuse feeds one side of the pre-amp tube heater supply...

 

[fweijers]

Guys

strange thing is, I took the amp home, checked all fuses HT, main, then opened the amp and checked all fuses inside. All fine.
Put the amp back together and guess what: all is fine. I'm using the amp for 2 weeks now and still no problems.
I guess a loose contact or so ...

 

[Ken]

Guys

strange thing is, I took the amp home, checked all fuses HT, main, then opened the amp and checked all fuses inside. All fine.
Put the amp back together and guess what: all is fine. I'm using the amp for 2 weeks now and still no problems.
I guess a loose contact or so ...

Are all 4 power tubes now glowing?

If so, I can guarantee this issue will pop up again sooner or later, but until it does it may be hard to troubleshoot. Chances are one of the solder connections are bad, but for now it's making contact.

If your amp is somehow running on 3 tubes, DON'T USE IT! Your impedence is off and Marshall transformers have a reputation for being fragile when your power tubes blow from the mismatch.

Ken

 

[jazzy cian]

Just look what happened to this guy...
Guitar Amp Electrocution - Ouch!.wmv - YouTube

Ha Ha Ha Ha Ha Ha Ha..........Brilliant

 

[Lucifuge]

+1 on what Ken said. A lot of times solder connections are the culprit in problems like this one. The good thing is, they're pretty easy to find and easier to fix if you can solder right....

Just make sure you discharge the caps before you start soldering....

 

[fweijers]

Well, after a couple of months the problem is back.
Today the amp made no sound at all, and I saw the first tube was dead again.
The other three happy and glowing.

I took off the back cover, took the dead tube out (the first power tube from left, next to the pre amp tubes), took out the second tube, swapped them and put them back in.
Guess what? All four tubes glowing!

My guess is this is a bad soldering or so on the tube socket.

But: why is the amp completely dead when the first power tube is dead??
I have had a dead tube once before, but in that situation the amp did work fine on 3 tubes (almost as if all 4 tubes were fine).
So, where should I look for this bad soldering ...?

 

[diesect20022000]

Well, after a couple of months the problem is back.
Today the amp made no sound at all, and I saw the first tube was dead again.
The other three happy and glowing.

I took off the back cover, took the dead tube out (the first power tube from left, next to the pre amp tubes), took out the second tube, swapped them and put them back in.
Guess what? All four tubes glowing!

My guess is this is a bad soldering or so on the tube socket.

But: why is the amp completely dead when the first power tube is dead??
I have had a dead tube once before, but in that situation the amp did work fine on 3 tubes (almost as if all 4 tubes were fine).
So, where should I look for this bad soldering ...?

when you checked the fuses did you just look at them or did you use a meter? visual inspection doesn't mean much.

I'm not a tech or anything but there really aren't any here now. are these new tubes or different tubes?

it was my first thought that there was something not wired right there as i've had this issue on my Dragon. it still worked though but the power sections are different.

pull up the schematics and see what the power section looks like. that may help.

 

[Ken]

Next time it dies unplug the dead tube and plug it back in. I bet the amp will work again.

Obviously the issue is at or near the #1 tube socket. Someone with basic soldering skills should discharge the caps and take a look. It could also be the socket itself; try cleaning it with tube socket cleaner. Fuses don't usually work intermittently so I doubt it's a fuse.

When it dies again, it might be a good time to use a meter to trace the paths from the tube; that will pinpoint where the fault is, but this means working on the amp when it's on and this is not for someone who is careless.

Ken

 

[fweijers]

Next time it dies unplug the dead tube and plug it back in. I bet the amp will work again.

Obviously the issue is at or near the #1 tube socket. Someone with basic soldering skills should discharge the caps and take a look. It could also be the socket itself; try cleaning it with tube socket cleaner. Fuses don't usually work intermittently so I doubt it's a fuse.

When it dies again, it might be a good time to use a meter to trace the paths from the tube; that will pinpoint where the fault is, but this means working on the amp when it's on and this is not for someone who is careless.

Ken

Thanks for the reply.
The problem is not in the fuses I measured them.

Yeah, a bad soldering or the fuse socket could be it. I have soldering skills, but I doubt it is possible to measure voltages while the amp is on ... this is quite tricky and traces may be very hard to reach.

Anyway, I am still puzzled why the amp is completely dead when the #1 tube is out. I might have other issues with this amp. Hopefully I will be able to solve it.
Is anyone out there willing to pull tube #1 and then try the amp?