Purchasing a used tube amp

  • Thread starter Thread starter didgijimmy
  • Start date Start date
didgijimmy

didgijimmy

vexed
Hey guys, I've been browsing Craigs list lately and am thinking about buying a new amp. Before I go look at any, what are some things I should check for on the amp. I've bought new tube amps but not used, and am a little scared. Are there any tests for tubes, or the amp in general I can perform. Any history I should be wary of? Or is buying a used Tube amp just a bad idea?
Thanks for your help,
James
 
Most possible problems would be audible. So just listen to it at various levels and use all the inputs. If you can look at the guts, check for arcing, especially on sockets. You might also look at the caps to check for any signs that they are ready to give out. ( but that would probably be audible) It might be helpful to know what type of amps you are looking at. I'm an old Fender guy and something newer with more bells and whistles is outside my experience.

If you don't know what not to touch, don't go poking around inside. Filter caps can hurt you.
 
FWIW,

I've bought all my amps used using basically the method Goya recommended. I would only add that it's a good idea to leave it on awhile to see if anything gets hotter than it should. Don't be afraid to explore off brand amps that meet your specs. some of them sound really cool.
 
Yeah, as said TRY, run it hard, run it easy, run it long, run it in all inputs & configs and take YOUR guitar & cable.
I haven't bought a new amp yet (playing for 35 years) and haven't been disappointed either.
Oh, & as said re inards LOOK but DON'T TOUCH!
 
One of the simplest things you could do is let it warm up and look at the power tubes. The owner might need to remove a protective piece to make the tubes visible for you, and hopefully he would oblige you. Just make sure that the tubes are all glowing with the same intensity, a warm orange-red glow. No blue, no white, no red, just a pleasant soft orange color. (If there are any tubes that are SUPPOSED to run at a different color, correct me!).

If you get it nice and warm, play through it, push the power section, then check the power tubes and make sure that your workout didn't stress them to the point of acting up. The amp's distortion character will change subtly as it gets warmer and warmer. On standby, it might take quite a while for it to reach equilibrium.

As for the preamp tubes, they might not be as easily accessible as the power tubes. If they are, make sure that they also have a uniform orange glow. Some preamp tubes have very specific jobs inside the preamp section (rectifiers, reverbs, tremolos, phase inverters, things like that). For all I know, they may glow with differing intensities depending on their preamp function. Just make sure that none of them look "out of bounds" or lifeless.

There are probably several other things that could be wrong with a tube amp, but odd tube glow would likely be an indication of larger problems (or it could just be a bad tube). It's a good place to start but not an exhaustive diagnostic.
 
I've noticed that my tubes normally glow blue, so I looked it up and that is pretty normal, at least for some tubes. I'm using a Fender Blues Jr. But I could be wrong.

Edit: Nevermind, they glow orange, except for the middle section of the EL-84s.
 
Tadpui said:
(If there are any tubes that are SUPPOSED to run at a different color, correct me!)
Click to expand...

There are some tubes that glow various colors because they are not vacuum tubes. They are filled with certain gases. I don't know of any of these type of tubes that are used in tube amps but there might be.
 
My princeton reverb has blue tint to them. Actually all my amps do. They've all been recently serviced too by probably one of the best amp guys around. :)
 
Well now I know!

I see that when the blue glow is due to flourescence, kind of like the northern lights, its not a bad thing. But if its glowing blue due to being a gassy tube, it should be replaced. I just read a neat way to see if the blue glow is good or bad. Hold a magnet next to the tube. If it affects the blue pattern, that's OK. But if it doesn't, it indicates a gassy tube and should be addressed.
 
Wow, thanks guys, lots of great advice here. I'm sure I'll be able to make a wise purchase now. Someone mentioned arching, what will this look like?
James
O and the amp I'm searching for is a Peavey Classic 30
 
6L6/El34tubes sometimes will glow bluish normally although less frequently for the 34s. el84s/12ax7s will usually glow orange, some will have blue near the base. No PURPLE should be seen on any of these tubes. None should be glowing excessively around the plate (at the base of the tube), this is an indicator they are not running properly.

Here is a thread from another forum that talks more about tube glow http://www.diyaudio.com/forums/showthread/t-46750.html


Don't just take my word for it. This is something you want to do a lot of your own research on. Make sure you ask the owner everything about the amp's service history and if he can provide documentation on when it was last serviced and by who. Try to do this in a friendly way though. There are a katrillion different factors that contribute to tube amp problems. We've all had friends that don't care about their amps... those people who "never had to change a tube in their life." These are usually the people that get oil changes every 20,000 miles or tend to trade in their cars for new ones every year.
 
Last edited:
buckkillr8 said:
I'll second that. The classic 30 and 50 take pedals very well. :)
Click to expand...

Tadpui said:
Great amp. I've played through a Classic 50 4x10 and with the right gain staging it sounded awesome.
Click to expand...

Yeah, I've played through them before and was very pleased with everything about the amp, except that the two channels share the same eq, but such is the sacrifice for a smaller amp. I love playing blues on the dirty channel, the clean is great for jazz, and I figure I can run a pedal for anything really heavy, although it gets pretty heavy on its own. And if i go used i can pick one up for like $300. But if i buy knew i wont be heartbroken. And yeah, the 50 with 4x4 is super tempting, but I just don't need the much at the moment (college).
Thanks guys.

owwmyfoot said:
6L6/El34tubes sometimes will glow bluish normally although less frequently for the 34s. el84s/12ax7s will usually glow orange, some will have blue near the base. No PURPLE should be seen on any of these tubes. None should be glowing excessively around the plate (at the base of the tube), this is an indicator they are not running properly.

Here is a thread from another forum that talks more about tube glow http://www.diyaudio.com/forums/showthread/t-46750.html


Don't just take my word for it. This is something you want to do a lot of your own research on. Make sure you ask the owner everything about the amp's service history and if he can provide documentation on when it was last serviced and by who. Try to do this in a friendly way though. There are a katrillion different factors that contribute to tube amp problems. We've all had friends that don't care about their amps... those people who "never had to change a tube in their life." These are usually the people that get oil changes every 20,000 miles or tend to trade in their cars for new ones every year.
Click to expand...


Yeah, I work in the service department at a car dealership so I know exactly what you mean. Thanks for the tips. Will let everyone know how it goes.
James
 
You must log in or register to reply here.
Back
Top