Series One 200 blown tube?

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Posts: 1
Joined: Sat Nov 07, 2015 4:23 am
Location: United States

Sat Nov 07, 2015 4:34 am

Hey guys,

Just completed a cross country move and it seems that one of my tubes may be loose or blown in the moving process. The 3rd, or 2nd tube (depending on which way you count) does not warm up and the is a low buzz coming from the amp when powered on. Is it possible that it just came un-seated?


I don't have a lot of experience in replacing tubes but I'm fairly electrically savvy. I've read that you need to replace them as matched sets (or all 4?). Is this something I could accompish on my own, or am I better off taking it to a guitar shop?

And advice/help would be greatly appreciated! Thanks!

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Posts: 208
Joined: Sun Sep 29, 2013 1:14 pm
Location: Bedford, New York

Sat Nov 07, 2015 12:52 pm

I don't believe you have to change all of the tubes, but you do have to have the tubes biased, and unless you know what you are doing, you should send it to a tech.

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Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Sun Nov 08, 2015 5:45 pm

Since the amp was moved. it's entirely possible that you just need to reseat the tubes. However, just the act of opening the amp up will void any warranties. So if the amp is still under warranty, take/get it to an authorized repair center. If it's no longer under warranty, go ahead and try reseating the tubes. If that, doesn't work, try swapping it with the tube next to it. That will tell you if it's something with the tube or the socket. If it's something with the socket, it needs to go to a tech.

Like John said, power tubes need to be biased. In other words the idle current needs to be set. The task is fairly easy, but if you don't know what you are doing it can be dangerous. There are lethal current levels flowing when an amp is powered on and setting bias requires probing around inside the amp while it's live.

Regarding matched tubes, they are recommended because in most tube amps you can only set the bias current going to a pair of push/pull tubes. If that set of tubes is perfectly matched, then the bias current is split evenly across both tubes. In reality however, matched sets usually have up to a 5% variance between them. So, in an amp with only Bias controls, you can never get perfectly matched current flow going through both tubes.

I don't know about the Series one specifically, but most Blackstar amps allow you to set both bias and balance for each pair of push/pull tubes. So you can specifically adjust the how that bias current is balanced across a pair of tubes. That said, if the pair of tubes used are way off from each other there may not be enough sweep in the balance adjustment to even it out. So it's still a good idea to use a matched sets...or in your case a matched quad.

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