Do I have a bad tube?

[station5343]

Hi, can someone tell me what may be happening to my amp? It is a Marshall JCM2000 DSL 50 and the last couple of times that I turned it on something has been happening. I'll turn it on and start playing and everything will be fine then as I am jamming out all of a sudden the volume will start dropping and fading in and out. It will drop down real low to where I can hardly hear anything then it will come back up to full volume. So if anybody who reads this can offer any advise as to what this may be I would greatly appreciate it. I suspect it may just be one of my pre amp tubes as the power tubes are all glowing nice and bright. I dont think it's anything too serious because I just had it in the shop a couple of months ago for a once over/inspection and I would think the tech would have seen if there was anything wrong inside with the internals of the amp. But please feel free to offer any advise as to what you all may suspect it to be...thanks!!

[g1]

Put a patch cord between the FX send and FX return jacks and see if that helps.

[station5343]

Thanks g-one the problem with that is I am using the FX loop for well FX. In fact now that you brought it up that was one of the reasons why I had her in the shop, because the FX send jack needed replacing. But thanks anyway, any other suggestion's?

[52 Bill]

Thanks g-one the problem with that is I am using the FX loop for well FX. In fact now that you brought it up that was one of the reasons why I had her in the shop, because the FX send jack needed replacing. But thanks anyway, any other suggestion's?

It could be a bad tube or a dirty tube socket, but I think that that is one of the amps that has a common problem with the grounding of the speaker jacks. Which speaker jack/s are you using?

[eschertron]

I think G-one is referring to this problem that many have faced: The Dreaded Switching Jack Problem

I battled it for a while, almost tossed my amp before I found that thread. My solution included cleaning (burnishing) all the jacks as regular maintenance until the amp's behavior improved.

[station5343]

I think G-one is referring to this problem that many have faced: The Dreaded Switching Jack Problem

I battled it for a while, almost tossed my amp before I found that thread. My solution included cleaning (burnishing) all the jacks as regular maintenance until the amp's behavior improved.

Hi, Just wondering what you are refering to as the dreded switching jack problem? If you would elaborate a little more I would appreciate it. Also explain what you mean by burnishing the jacks...thanks.

[station5343]

It could be a bad tube or a dirty tube socket, but I think that that is one of the amps that has a common problem with the grounding of the speaker jacks. Which speaker jack/s are you using?

As far as you're answer 52 Bill what do you mean one of the amps with a common ground problem, also I don't understand you question as far what you mean bt which speaker jacks am I using I am using the speaker jacks that the amp came with? Please explain what you mean...thank you.

[station5343]

It could be a bad tube or a dirty tube socket, but I think that that is one of the amps that has a common problem with the grounding of the speaker jacks. Which speaker jack/s are you using?

52 BILL, I never had any problems in the past with grounding on the amp or speaker jacks.

[g1]

You've so far got 3 separate suggestions and refused them all.
Forget everything from before, the amp has a new problem.
1) from post #2, remove your effects from the loop, insert a cord between send and return. Try it and report your findings.
2) from post #5, there is a blue highlighted text. Click on it and read the info., it will explain the switching jack problem.
3) from post #4, there are several speaker jacks on the back of the amp, 52Bill wants to know exactly which one you are using. What is it labelled as?
If you don't answer any of the questions being asked, or try any of the suggestion, no one will be able to help you.

[station5343]

You've so far got 3 separate suggestions and refused them all.
Forget everything from before, the amp has a new problem.
1) from post #2, remove your effects from the loop, insert a cord between send and return. Try it and report your findings.
2) from post #5, there is a blue highlighted text. Click on it and read the info., it will explain the switching jack problem.
3) from post #4, there are several speaker jacks on the back of the amp, 52Bill wants to know exactly which one you are using. What is it labelled as?
If you don't answer any of the questions being asked, or try any of the suggestion, no one will be able to help you.

Ok cool sorry about that, I guess sometimes I can be a little thick headed. I will try you're suggestions and report what happens...thanks. The patch chord between the send and return jacks didn't do anything, also I just checked and I am going into the 4 and 8 ohm speaker jack's because my cab has 8 ohm speakers, 2 Celestion greenbacks and 2 vintage 30's all 8 ohms. . I will check out that link to the text about the switching jack problem.

[Jazz P Bass]

I just had one of these DSL50's come through.

The soldering was so bad I reflowed every board.

[station5343]

I think G-one is referring to this problem that many have faced: The Dreaded Switching Jack Problem

I battled it for a while, almost tossed my amp before I found that thread. My solution included cleaning (burnishing) all the jacks as regular maintenance until the amp's behavior improved.

I tried but cannot open the link to read the text about the switching jack problem, it just opens up to a dead PDF link.

[eschertron]

I tried but cannot open the link to read the text about the switching jack problem, it just opens up to a dead PDF link.

So it does. Jazz P!! Please repost! Thanks!

[Jazz P Bass]

I reposted the link about half way down the thread.

Oh, well: http://music-electronics-forum.com/a...ck-problem.pdf

[52 Bill]

Sorry if I was unclear earlier, we tend to use terms that a non-tech may not get.

Your amp has an unusual wiring circuit on the output/speaker jacks. The 4/8 ohm jack is connected to ground through the 16 ohm jack. When there is nothing plugged into the 16 ohm jack, there is a normally closed switch on the 16 ohm jack that closes the circuit for the 4/8 ohm jack. If the switch doesn't close correctly the speaker that is plugged into the 4/8 ohm jack no longer has a complete circuit to ground and the sound will either weaken or cut out completely.

If you read the FX loop jack post, it's almost the same thing, but related to the speaker jacks.

There is also a fairly common problem with the tube filament rectifier coming unsoldered that will also cause your problem.