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Discussion in 'Amp Central Station' started by vashondan, Sep 14, 2020.
It is weird. I can't imagine that I would have replace a single tube.
Have you ever heard the saying about how to a man who's only tool is a hammer everything looks like a nail?
I think that is basically what happens with the advice that has people replacing entire sets of tubes regularly. Installing a new set of tubes is a tool available to any amp owner, real troubleshooting not so much.
The chances of any of your preamp tips being bad is relatively low as they don't get stressed that much. The tubes that are only acting as simple gain stages should last just about forever, the reverb driver and phase inverter tubes may not have quite the same lifetime. The power tubes do eventually wear out, especially in an amp which runs them at voltages that are traditionally a bit inadvisable for 6v6 tubes, but they should still last for quite a while.
One thing I would consider, and that needs to be addressed even if you do just straight up replace the tubes, is bias. Your tubes may be worn but not necessarily worn out. This where or other components starting to drift may have change the bias to the point that it doesn't sound good anymore and a simple adjustment of the bias may allow the amp to sound the way you want it to. Even if you replace with a new set of tubes they need to be biased both to determine that they are running at a safe dissipation level and to get them to sound their best.
Point taken and since I know little to nothing about these things I respond accordingly. Well, the tubes are ordered and as for the biasing that will have to wait to explore. The good thing is I learn along the way. At least I think I do.
Has the amp ever been out of your control....loaned to a friend, left in a practice area, been in a repair situation? If not, then someone messed with the amp before you bought it.
Afterthought...I might have replaced that first tube in response to a thread that I read quite some time ago. A trace memory says that I might have.
Nope, never left my house.
There you go...you bought a new amp that had been messed with.
Whoops....just read the post you made admitting that you may have replaced one power tube. If so, imho, you acted on bad advice. As I noted, there is nothing wrong with mixing tubes from different manufacturers. However, when doing so one would want to take note of the bias numbers for each tube. Of course, I want to know those numbers when installing a matched set of tubes, so that biasing is natural step for me no matter what tubes are used.
Another point taken! I'm looking at the man in the mirror!
If you're open to learning and don't let yourself become too intimidated by the internet gatekeepers reminding you of the potential dangers in a discouraging way, this forum and others can be a great resource to learn to do your own amp work.
It's definitely worth having an extra set of tubes regardless of whether you need them all or not, swapping out tubes can be a very effective form of troubleshooting even if the tubes aren't the problem themselves. When that set arrives you should start swapping them out as @Wally suggested and then you should start reading up on how to set the power tube bias because that needs to be done regardless of whether you actually need to replace them in order to ensure longevity of the tubes themselves and to get the best sound out of any fixed bias amp.
So, what I’ve heard from forum folks is how dangerous it is setting bias. I’m open to learning but don’t want to get beyond myself. Are you suggesting that it’s doable for a neophyte?
It's definitely doable it's just that there is potential danger from the high voltage inside the amp chassis but it's not rocket science to avoid shocking yourself. Some amps come with exterior bias test points that make it much more convenient and reduce the risk of accidental shock, I don't know if your amp is one of them. It's just a question of whether you are comfortable with the idea of opening up an amp chassis and measuring the voltages within while it is on, but it can certainly be done safely.
If you are interested in learning to work on your amps yourself there are a lot of good resources on the internet, one of the best is @robrob's website here
You may want to also search for some YouTube videos on the subject those can be very helpful as well.
My understanding is that some of these PRRI amps are biased hot, meaning it will eat tubes. I would take it to a tech and have the tubes all checked and have it biased properly, whether tubes are replaced or not. I wouldn't just throw in new tubes to sacrifice to the monster.
Vashodan, the simplest and safest way to bias that amp is to acquire a bias probe tool that reads current draw and plate voltage. You do not have to pull the chassis to bias with such a tool since your amp has,iirc, a bias pot that is externally accessible. If you get a tool that has dual sockets, that is even better...and more expensive.
I like Randall Aiken’s explanation of biasing.
Aiken’s White Papers in his Tech section is full of good basic information...and some not so basic.
Read as much as you can. Imho and ime, if one wants to start learning about the workings of a tube amp, one starts here....
One also needs to have access to tube pinout information....
Have copied and bookmarked all the info from your posts and other and will do some exploring. will see where this leads. Many thanks.
Thanks, I've got the references. Will take a look