First gig with Vox AC30, Alnico Blue died

mightypudge

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I purchased a "demo" Vox AC30HW2X with Alnico Blues from a reliable retailer on Monday last week. It sounded fantastic at rehearsal on Wednesday, but Saturday night during its inaugural gig the right speaker blew. Thankfully, the retailer is exchanging it for a new one. But I really don’t want to go through this again.

At the time when the speaker blew I was running my pedalboard into the Normal channel of the amp. The amp was in 30-watt mode with the channel volume a bit less than 1/3 of the way up, at the most. The Master Volume was disengaged. I was basically at gig volume for a small room. My pedalboard consists of two overdrive and two distortion pedals. One pedal is always one, sometimes two for solos. I also have a few modulation effects and a delay. The amp was not cranked by any means and the overall tone of the amp without pedals was clean.

The whole reason I bought the AC30 was to run it this way - pedals > amp and although I knew the Alnico Blues are 15 watt speakers I did not consider my usage to be outside of the normal working parameters of the speakers.

So...did I blow the speaker and am I likely going to run into this issue again? Or is it entirely possible the speaker was bad, or possibly weakened by the previous owner?
 
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Cirrus

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Running the master bypassed and channel volume 1/3 of the way up will pretty much be running the amp at the top end of its clean headroom (give or take how hot the guitar pickups are of course!) - any higher and it'll start to overdrive. So you were probably putting around 15 watts into each blue.

That said, I run my AC30hw like that too and after 3 years I've not blown a speaker. I've also at times totally cranked the amp, ran octave down fuzz tones into it and probably not treated the Blues with the respect they deserve. Blues are rated conservatively and AC30s because of their voltage sag, compression, midrange emphasis and lack of punchy low end/ sharp transients are safer to use cranked with 2x15 watt speakers than some might imagine.

I think you were just unlucky.
 

MasterEvan07

Where's that buzzing coming from...?
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I've also mercilessly abused Blues before, several decades old Blues at that, without issues - high gain, fuzz, etc.

I am planning on going the Creamback/Cream combo in my next AC30 though, not because I mistrust the Blues but because I've been extremely impressed with the Cream series!
 

mightypudge

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Thanks for the responses. I didn't think I was doing anything excessive, but then this is my first time using the Cele Blues so I just needed a reality check.
 

TimmyP

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IME Blue failures in AC30s are very rare (in 11 years I think I've replaced only one in many amps with many gigs on them).
 

jay42

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Just wondering, are they wired in parallel or series (which would be bad)?

OP, if you remember what you were doing when it went, were you running a pretty saturated sound or doing a chinka-chinka rhythm part? For example, almost anything Ramones or Sex Pistols like, is going to heat the speakers up and not give them enough cooling cycles.
 

jay42

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FWIW, all AC30s I've known of have came with two 8 ohm speakers in series.
So if one speaker blows, there's no load on the amp...and no sound obviously. No load is basically a bad thing for a tube amp.
 

Cirrus

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I guess it depends whether it blows open or closed circuit. Luckily, if the sound stops you probably stop playing through the amp (if you're sensible :D )
 

DaveKS

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I'd say you got a anomaly on that speaker blowing, it happens, if every speaker was perfect from factory there would be no need for warranties.

But I'm also of the opinion that, with that amp with, that combo of speakers your living close to the edge also. There's a certain mojo with with speakers living on the edge, and with your use of combos of OD and distortion your probably approaching that edge more than you think. And I do think that Celestion rates their speakers conservatively, so on paper yea, you shouldn't have a problem.

Those new Celestion Creams or some higher rated Weber Blues might look like a more attractive option in the long run.
 
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pdf64

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So if one speaker blows, there's no load on the amp...and no sound obviously. No load is basically a bad thing for a tube amp
Agree, the load flipping to open circuit on a wailing power amp is one of the worst case scenarios.
Despite that, my old AC30 has survived such an event a couple of times (neither was due to a Blue failing).
I guess that the fairly low VB+ of AC30 is probably in their favour in this, eg lower VB+ may result in lower flyback voltage).
Series connection of low power speakers makes the issue far more likely to manifest, compared with parallel connection.
However, that may be balanced against the tube amps being used with single speaker; it may not seem reasonable to described that scenario as bad, yet the failure mode and its likelihood are pretty much the same as with series connected speakers.
And in reality, if the same low power speakers are connected in parallel, once one blows then the other will be subject to the full (though perhaps a little reduced) output power of the amp, and its failure may not be far behind.

In favour of a series connection for speakers on tube amp (especially one operating open loop) is that the low damping factor of the amp may allow a freer rein for the resonances of the speakers to develop; a parallel connection will tend for each speaker to damp down the resonances of the other/s.

I guess it depends whether it blows open or closed circuit. Luckily, if the sound stops you probably stop playing through the amp (if you're sensible :D )
My experience is that low power vintage type construction speakers tend to fail open circuit; it seems to be higher power ones that can suffer from shorted turns due to the voice coil overheating.
Unfortunately, the response of many musicians of my aquaintance to 'no sound' is to 'turn it up'!
 






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