Blown valve head - value?

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Marquischacha
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Blown valve head - value?

Post by Marquischacha » Thu Dec 05, 2019 6:25 am

Hey OSG.

I have a Carlsbro PA60 head that blew at a gig a few years back. I had to quickly source a new head for the remainder of the tour so this Carlsbro has been collecting dust in storage for some time. Does anyone have any resources for getting ballpark figured for blown vintage valve heads? A local vintage amp group I'm a part of seems hesitant to even give me an estimate value, so I'm trying to find as much information as possible so I can get rid of it.

Cheers!

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HH1978
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Re: Blown valve head - value?

Post by HH1978 » Thu Dec 05, 2019 3:15 pm

Hello,

I don't know much about the model, so I can't help with pricing anyway, but I think more information is needed about what exactly has blown in the amp, as restoration cost will depend on that.

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andy_tchp
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Re: Blown valve head - value?

Post by andy_tchp » Thu Dec 05, 2019 4:21 pm

'Blown' is a meaningless diagnostic, this is why nobody can provide an estimate.

Big difference in cost/effort for a 'blown' output transformer compared to a tube (and bench time figuring out what and why)...
"I don't know why we asked him to join the band 'cause the rest of us don't like country music all that much; we just like Graham Lee."
David McComb, 1987.

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Re: Blown valve head - value?

Post by Marquischacha » Fri Dec 06, 2019 2:26 am

Thanks for the replies, guys. Yeah, this is the problem really. I am completely clueless with valve amps. I suppose what I'm asking is how to figure out a rough value for something I can't diagnose myself. I'm not after an estimate for repair or a service, I'm just wondering how much I could potentially sell this on for, with the understanding that it will likely need work done by someone who knows how to work on it.

As far as I'm concerned the amp is "broken", and I just don't have the money due to various unfortunate circumstances to get it seen to by local amp service centres. I have no space of my own at the moment to open it up to even think about taking a look, and I can't commit to a repair cost at the moment so I feel like I just want to cut my losses and at least pass on the unit to someone who might want it for spares or repair.

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HH1978
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Re: Blown valve head - value?

Post by HH1978 » Sun Dec 08, 2019 11:33 am

What were the circumstances when it blown and what were the symptoms, if you remember?

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Re: Blown valve head - value?

Post by Marquischacha » Mon Dec 16, 2019 6:28 am

Hey, thanks for the reply (and apologies for my delay!)

I was playing a gig and we didn't have the backline we were promised, so I ended up having to use a speaker cab belonging to the venue. The (uninterested) soundguy told me the cab had a certain impedance to work with my valve amp, but halfway through the gig I smelled burning and my sound cut out completely. Unfortunately I can't remember what the soundguy told me about the cab, but it certainly seemed as though the issue is with mismatched impedance.

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Re: Blown valve head - value?

Post by Mechanical Birds » Wed Dec 18, 2019 8:17 am

So output transformer most likely. Find one for sale and subtract, what, $150-$200 from it? No idea about these amps tho

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Re: Blown valve head - value?

Post by HH1978 » Wed Dec 18, 2019 11:56 am

Possibly, unless it was protected by a fuse.

If the OT burned, there must have been some hints in the sound before it went silent. It's unlikely that the 2 sides of the OT stopped working at once. One side dead means the amp ran for a moment on one power tube tube (or one pair if using a quad), which translates into crossover distortion, and is quite noticeable. Probably a loud hum too. If the (hypothetical) fuse blew, the tubes plates were not fed by B+ anymore, and the amp went silent. Now blowing a fuse means someting went bad elsewhere anyway.

Also, assuming it's a tube amp (not sure if there was a SS version of the PA60), impedance must have been highly mismatched to fry the OT. Impedance matching refers to the optimal load reflected on the OT primary (and power tubes plates), which practically means the more clean headroom and power the amp can give. Tubes datasheet usually provide data for different plate to plate resistances, and the tubes can be run safe with different reflected loads, as long as you don't go to far in mismatch. Solid state is a whole different story.

From what you describe, I can't exclude other possibilities, like a dead preamp tube (V2 being the most likely, unless you didn't try all the inputs). The burning smell could come from an arc, or a blown capacitor.

I doubt anyone would take a risk on this amp without knowing what is exactly going on inside, especially considering that you can find a working example around 500€ on Reverb.

My advice would be to find something else to sell, and keep it until you can at least diagnose it.

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Re: Blown valve head - value?

Post by HH1978 » Wed Dec 18, 2019 12:04 pm

I should add, there are other methods to protect the OT (diodes, for instance). The point being, there's no way to be sure the OT is fried or not without opening the amp and diagnose it. But it's certainly a possibility, and if so, an expensive repair.

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Re: Blown valve head - value?

Post by Marquischacha » Thu Jan 09, 2020 2:19 am

Thank you for the info - I really appreciate it! I may well keep hold of it for now, but I am getting another amp serviced soon(ish) so I may take it along to the guy just to get another opinion.

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