#1
Hi all,

I use a classic 30 with JJ tubes, stock speaker, and I have a Tube Tamer as well. The JJ's are more or less new, I bought them about 4 months ago.

Last night, I turned on my amp and got a loud humming sound, not the intermittent popping sounds of rattling tubes. I messed with all the dials, turning everything down (volume, distortion, EQ, reverb, etc) and still no dice. Seeing as there was nothing I could do about it, I left my amp to let it warm up.

After I let it warm up for 20 minutes or so, I came back and started playing (the hum was still occurring). 5 minutes later, the sound completely cuts off from both the clean and dirty channels.

I checked the tubes, and lo and behold, they were all completely off. As in, although the amp was definitely on (the power light was on), the tubes weren't glowing at all.

I have an extra set of JJ's on me that I'm going to replace the old tubes with, but I'm not sure if the tubes are even the problem. Any ideas?
#3
Sounds like it is time for new power tubes and a HT fuse. Main fuse seems to be OK. You may want to get an amp tech to help you as there are deadly voltages in there (in the capacitors).

IE. Simply replacing the HT fuse will not fix anything. You will blow that one too if you don't find the source of the problem. Hopefully, it is just the power tubes and not anything more serious.

Good luck.
#4
After a lot of procrastinating, I finally got into the guts the amp. I noticed there were 3 fuses, although the Classic 30 circuit diagram only shows two (from what I can tell). One was located at the power cable input, and two were right beside each other right by the transformer input (I think it's the transformer). Two of the fuses looked unbroken, but one was completely coated in white stuff - you can't even see the glass, it's all coated on the outside.

I also tried just replacing the power tubes without touching the fuses, that didn't do anything.

I'm thinking the culprit is probably the "white coated" fuse. How do I tell which one is the HT fuse?
#5
Fuses don't blow 'just because'. You likely blew a tube and it caused the fuse to blow. However, fuses are cheap, so try replacing the fuse and playing with your amp for a while. If its fine problem solved. But if it blows again replace it and the power tubes.
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#6
I realize that usually fuses blow because there's too much current flowing through it. Assuming a tube blew (which I'm sure it did), the current would treat the tube as a short circuit and instead go through the fuse, right? In addition to whatever current the fuse had before, that is.

Also, are the fuses placed before the power tubes in a circuit? It seems like if they weren't, you'd have current flowing to one or two of the tubes.
#7
I replaced the 10A ceramic fuse, and nothing happened with the new power tubes installed. The 3A fuse and 1A fuse both look okay. None of the resistors or capacitors look fried, either. I'm at my wit's end.
#8
It seems to me like it could be the power transformer. I haven't taken it apart and looked at it. If it is the transformer, is it possible to replace it or would I have to buy a new amp altogether? I'm gonna buy a voltmeter and check the voltage/current before and after the transformer, but other than that how can you tell if it's gone kaput?

I think I'm going to take this amp to a repairman if this doesn't work.
#9
Quote by AK501
It seems to me like it could be the power transformer. I haven't taken it apart and looked at it. If it is the transformer, is it possible to replace it or would I have to buy a new amp altogether? I'm gonna buy a voltmeter and check the voltage/current before and after the transformer, but other than that how can you tell if it's gone kaput?

I think I'm going to take this amp to a repairman if this doesn't work.


Yes you can replace the power transformer.

Mercury Magnetics sells power transformers for some amps.
I just hope your amp is one of the amps they sell power transformers for….

http://www.mercurymagnetics.com/
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#10
Quote by injected
Fuses don't blow 'just because'. You likely blew a tube and it caused the fuse to blow. However, fuses are cheap, so try replacing the fuse and playing with your amp for a while. If its fine problem solved. But if it blows again replace it and the power tubes.

This.