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The other day my blues Jr  stared to buzz . I  think that is why I replaced all the tubes a few years ago. (Later I was told it’s usually only the power tubes that cause buzzing) So, I have these old power and pre amp tubes laying around and I know they couldn’t all be bad, so I tried to find one good power tube to start the troubleshooting process. I plugged in one tube and blew the main fuse, tried another, same results.I stopped and install a new fuse and a new pair of power tubes. Now, I have a cracking sound and really really low volume. I plugged the guitar in my old amp just to be sure it wasn’t the guitar or cable and it worked fine. Can replacing the power tubes cause the failure of old pre amp tubes. Could my screwing around with old tubes have caused  other problems  than blowing a fuse? Really tempted to start plugging in old pre amp tubes to see what happens but, I guess I will go buy 3 new pre amp tubes? Any suggestions?

ps all the tubes are lit up.

Edited by Triple-o
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Yes

If a tube goes bad or in your case put in a bad tube, a number of things can happen 

Worst would be output transformer blowing, , that'd be really bad.

If you're lucky, the screen resistors saved the amp but melted down.

Don't go into the amp unless you know what you're doing , paralyzed or dead are to options in there for the uninitiated. 

Never keep old tubes, chuck's

Better take it to a tech

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Thanks, I thought as long as I just touched the tubes I would be safe. I only know one tech in the area and he takes months and like I mentioned before he doesn’t always figure things out. Probably should drive 70 miles to a big city.

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21 hours ago, Eracer_Team-DougH said:

Yes

If a tube goes bad or in your case put in a bad tube, a number of things can happen 

Worst would be output transformer blowing, , that'd be really bad.

If you're lucky, the screen resistors saved the amp but melted down.

Don't go into the amp unless you know what you're doing , paralyzed or dead are to options in there for the uninitiated. 

Never keep old tubes, chuck's

Better take it to a tech

@Triple-o I'd really pay attention to this advice... In case you didn't know Doug has many many years of experience with electronics.

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I should add,  

If you've been really lucky, getting a new set of tubes and swap them all, might work

What concerns me the most is the , put in a output tube and the fuse blew.

That says the tube had a high current draw.

Resistors can easily melt down on high current 

Other thing with tube amps , never run them without a speaker attached. 

Output transformers do not like being unloaded and typically melt down with no load,  which can also happen with a bad output tube

Some amps have a protection circuit in them to prevent this most don't. 

Always swap tubes powered down and cooled off., never swap powered on

Probably best you find a tech

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Posted (edited)

Thanks, I am going to take  it to a tech. I think I should start looking for a replacement.. 
 

 

 

 

 

Edited by Triple-o
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I think when it is time to replace a tube then replace all of them with new tubes at the same time. 

Your amp has been around for a few years so it might need some work. Doug has some good advice.

You could send it to Sweetwater. They do have service techs, but I don't know if they do this type of service. There are not many places around here either that I know of. 

P.S. A Fender Blues Jr is a terrible thing to waste. Fix it!

Edited by Randy120
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  • 4 weeks later...
On 8/21/2020 at 11:00 AM, Eracer_Team-DougH said:

I should add,  

If you've been really lucky, getting a new set of tubes and swap them all, might work

What concerns me the most is the , put in a output tube and the fuse blew.

That says the tube had a high current draw.

Resistors can easily melt down on high current 

Other thing with tube amps , never run them without a speaker attached. 

Output transformers do not like being unloaded and typically melt down with no load,  which can also happen with a bad output tube

Some amps have a protection circuit in them to prevent this most don't. 

Always swap tubes powered down and cooled off., never swap powered on

Probably best you find a tech

I am not sure what I did, but trying to find a good power tube I ended up shorting something out. It might have had something to do with the hanging bracket springs that hold up the two power tubes, or one of the tubes I tried using was some how damaged.

You were right I should have thrown away the old tubes, and just taken the amp to a tech. when it started buzzing.Cost me $77.00 to have it repaired.

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