I was playing around with my 1995 Vox AC30TBX this morning. I turned it off to add another piece of equipment into the chain, and as I did, I noticed a crackling, static-type sound. After that, it would not turn back on again. I left it "on" for a while and but there were no lights, no glowing tubes - nothing, even after 15 minutes. I checked all the obvious things, but I'm no amp expert so I don't know what else to do. Any ideas?
Vox AC30 Reissue - all of a sudden, no power!
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- Rated: 27 ↑
Sep 27, 2008 1:09 p.m. audiodrome:
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- Rated: 40 ↑
Sep 27, 2008 1:18 p.m. roadjunkie:
I always assume tubes first thing for one thing it's the cheapest fix and you should always have a spare set on hand. Check your fuses then your tubes. 4 matched EL84's just plug them in and see if it fires up no biasing needed with that amp. EH and JJ's are pretty sturdy.
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- Rated: 59 ↑
Sep 27, 2008 1:18 p.m. Bear:
Does your amp have a fuse, and if so did you check to see if it was blown?
If fuse is okay...
Did you smell an electrical (ozone) odor? If so, your transformer may have fried.
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- Rated: 6 ↑
Sep 27, 2008 1:44 p.m. Jukka:
Here is troubleshooting guide from VOX, this might be for the CC models, but I believe it could be some help for the TBX models as well. My experience is that the most common problem is the rectifier tube.
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- Rated: 42 ↑
Sep 27, 2008 1:52 p.m. JBGretschguy:
You probably blew a fuse, which could be because a tube went south. The fuses are inside the back panel, on the circuit board. Try them first, and if they still blow, try a new set of tubes.
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- Rated: 27 ↑
Sep 27, 2008 2:06 p.m. audiodrome:
I just checked the one fuse that's on the outsude of the chassis and indeed, it was blown. The only thing is, it doesn't look like any of the standard replacement fuses I have in my stock. It's about 3/4" long, the top reads S W (in circles) T4L250V, and the bottom just has a bunch of random symbols (a triangle with small letters in it, a peace sign-like symbol, a heart, and a "backwards" slanted UR! The fuse cap says 5x20mm. I have no idea what any of this means. Is this a special proprietary fuse only available through Vox?
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- Rated: 48 ↑
Sep 27, 2008 2:50 p.m. dmanlow:
Just roll up some aluminum foil and you'll be good to go.
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- Rated: 42 ↑
Sep 27, 2008 2:55 p.m. JBGretschguy:
It's just a standard 4 amp 250 volt Slo-Blo fuse. You can get them at Radio Shack.
http://www.radioshack.com/product/index.jsp?productId=2103760&cp=2032058.20322...
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- Rated: 27 ↑
Sep 27, 2008 2:59 p.m. audiodrome:
Thanks! Usually they will just say 4A 250V Slo-Blo. This one was all heiroglyphics!
The fuse shown in the Radio Shack link is a lot bigger than the one I need (mine is 3/4" not 1 1/4"). I have a feeling this is going to be some kind of "specialty order" fuse.
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- Rated: 19 ↑
Sep 27, 2008 8:02 p.m. cielski:
The fuse just isn't "American", as evidenced by the 5X20MM. Radio Shack may or may not have them as they've seemingly decided to sell phones instead of hobbyist parts. They may have it. A good electronics parts house should carry those. The real consideration is WHY it blew. Make sure your tubes are seated firmly. If fuses still blow, look over the circuit boards---something cooked should be obvious. Hopefully, it'll be a simple fix.
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- Rated: 27 ↑
Sep 27, 2008 8:27 p.m. audiodrome:
Do you think checking to make sure the tubes are seating firmly would be the best thing to start with? This amp does get banged around a little when I transport it to rehearsal one a week.
Also, where else do you think I might be able to find this fuse - maybe online somehwere? It's just that I can't afford to be without it. I desperately need it for a gig Tuesday night!
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- Rated: 40 ↑
Sep 27, 2008 9:48 p.m. roadjunkie:
There's alot going on in the Vox chassis and EL84's have a shorter then most lifespan. It doesn't hurt to check them out once or twice a week. The thing rattles shakes and rolls and things tend to go south. Most likely one of the tubes burnt out and the fuse blew. I used to really love EI's in my Tophat but they had a really short span.
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- Rated: 48 ↑
Sep 28, 2008 10:19 a.m. BillyZoom:
Radio Shack has both size fuses. Look harder. The Sovtek EL-84M seems to be the most durable. EI isn't a particularily good choice. If a tube went, check the 100 ohm screen resistors and the cathode cap. BZ
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- Rated: 27 ↑
Sep 28, 2008 10:28 a.m. audiodrome:
I think I found the right one. The size matches and it reads, "T4A L250V." The original fuse reads, "T4L250V," so I'm pretty sure it's the correct fuse. So now what should I do - replace the fuse and go around tapping the tubes? Or should I just replace the fuse and see how long it lasts? How can I tell if a tube is going bad?
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- Rated: 40 ↑
Sep 28, 2008 10:55 a.m. roadjunkie:
Put in a new set of power tubes before you turn it back on or you'll just blow the fuse again.
You right Billy Ei's weren't a good choice but they sounded damn good for there short lifespan!
Sovtek-EH- and I know Billy doesn't like JJ's but I had good luck with them. All pretty sturdy tubes! Don't go NOS until you have all this sorted out.
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- Rated: 66 ↑
Sep 28, 2008 11:04 a.m. Walter Broes:
I don't know how things work with a Cathode biased amp, but if I blow a fuse with one of my regular 6L6 Fenders, I take the tubes out, put in a new fuse, and turn the amp on. If it still blows fuses then, I'll know the tubes are not the problem.
Does that era AC30 have a rectifier tube?
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- Rated: 27 ↑
Sep 28, 2008 8:05 p.m. audiodrome:
But how do I know if it's a tube problem? I blew a fuse in my Super Reverb last summer, changed the fuse and everything was fine. I didn't have to change any tubes. What's different about the AC30? What if I change the fuse (which I'm going to do right now) and it doesn't blow again? Does that mean everything's cool as is?
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- Rated: 40 ↑
Sep 28, 2008 8:26 p.m. roadjunkie:
Try what Walter just said! Then if the fuse doesn't blow turn it off and try it with the tubes in. When dealing with el84s I assume it's the tubes because they are fragile and they put out a lot of heat! I found it best to change them out every 6 to 8 months anyway if I was using it hard during that period just to play it safe.
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- Rated: 27 ↑
Sep 29, 2008 10:48 a.m. audiodrome:
I just replaced the "power" fuse and I got it to power up (the power and standby lights now work), but then I got no sound, so I checked the other fuses, and sure enough the bottom left fuse of the four (500mA/250V) was also blown. Where do I go from here?
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- Rated: 19 ↑
Sep 29, 2008 10:52 a.m. Gretschington:
You re-read what's already been said then do it.
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- Rated: 27 ↑
Sep 30, 2008 10:22 a.m. audiodrome:
You guys were right , as usual!
I just talked to my guitar tech and he seems to think I will need a new set of EL84 output tubes. What brand should I get and where can I buy them? Apparently Guitar Center sells them but I'm a little wary...
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- Rated: 27 ↑
Oct 1, 2008 9:07 p.m. audiodrome:
I take it these are all good dealers?
But out of all of them, is this the best bet for my AC30TBX?
The Gold Pin Option and The High Gain Option look pretty good.
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- Rated: 27 ↑
Oct 2, 2008 10:41 a.m. audiodrome:
Any advice, thoughts, recommendations? This is all new to me so any help would be greatly appreciated - thanks!
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- Rated: 6 ↑
Oct 2, 2008 1:14 p.m. Jukka:
I have now JJ tubes on my AC30, I like them better than Electroharmonix I had. But I am not really expert on these either. Still I have a feeling, that your problem is more likely the rectifier tube than the EL84 tubes.
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- Rated: 41 ↑
Oct 2, 2008 1:20 p.m. J(esse James)D:
I'm thinking recto too
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