Amp Tubes

J

-Julian

New member
Hey guys,
One of my tubes went out on me on my peavey, which uses 12ax7 pre-amp tubes. Just wondering if its ok to buy a 12ax7 tube of a different brand and put it in there with the stock tubes.
Thanks
 
yes .... but there are subtle and not so subtle differences in sound between the same tube type and different tube manufactures. If you can locate and afford a NOS Mullard tube that would be my first choice. Any 12ax7 will work though.
 
Yes, any will work, and what Henry said is certainly worth much more consideration than people give it credit for. Aside from a speaker change, different brand tubes will have the biggest impact on a tube amp's sound. There's quite a difference in tone between cheap Chinese-made ones and NOS tubes of the 50s, 60s, or 70s. I've experienced this first hand.

Also, however, make sure the tube that went out is in fact a 12AX7, as many amps will use other 12A--- preamp tubes as well (such as a 12AU7 or 12AT7) for reverb send/recovery or tremolo.
 
yep, any 12ax7 will get the job done.

however, tonal differences between all of the different 12ax7's over the years are vast, and your tastes will vary.

personally, only use New Old Stock (NOS) RCA, GE, Sylvania Telefunken and Amperex tubes in my old fender amps. i find JJ's to be decent current production tubes, but they don't hold a candle to NOS, IMO.


cheers,
wade
 
Thanks guys appriciate the advice. Just one last quetion.
How do you double check to make sure the tube is out(it shouldn't light up right?) See i'm only guessing its the tube cause my clean channel is the only one that works and when i switch over to my lead channel i hear a big pop in the speakers and no sound.

THanks for all the adivice
 
-Julian said:
Thanks guys appriciate the advice. Just one last quetion.
How do you double check to make sure the tube is out(it shouldn't light up right?) See i'm only guessing its the tube cause my clean channel is the only one that works and when i switch over to my lead channel i hear a big pop in the speakers and no sound.

THanks for all the adivice
Click to expand...

Yes if the tube is working, it should light up when the power is on. Have you double-checked to make sure it's inserted all the way? Sometimes they can come loose during transit somewhere. Just out of curiousity, are you letting the amp warm up before turning the standby switch to "play" mode?

You can try trading one of the other (working) tubes in that position and see if your lead channel works.
 
go ahead and swap the tube... but... it's possible the problem is coupling caps... the reason i say this is the big pop when you switch tells me it's trying to pass some DC in all probability.... when a tube is dead nothing passes through it...
 
famous beagle said:
Yes if the tube is working, it should light up when the power is on.
Click to expand...

While it is true that if a tube is working it will light up, a tube that is not working may very well light up as well. The lighting up part is the heater circuit, and the amplification circuit(s) are completely isolated from the heater.
 
ggunn said:
While it is true that if a tube is working it will light up, a tube that is not working may very well light up as well. The lighting up part is the heater circuit, and the amplification circuit(s) are completely isolated from the heater.
Click to expand...

Thanks for the clarification. I kind of meant it from the opposite way though. (i.e., if it's not lit, it's not working.)
 
Thanks alot guys. I appriciate the addvice.
But, Demented how serious would it be if it was coupling caps. would it be an easy fix like replacing a tube? and how would i know for sure?
Thanks again guys you really helped.
 
-Julian said:
Thanks alot guys. I appriciate the addvice.
But, Demented how serious would it be if it was coupling caps. would it be an easy fix like replacing a tube? and how would i know for sure?
Thanks again guys you really helped.
Click to expand...

This isn't a difficult fix per se, but it's very dangerous unless you know what you're doing. It requires taking the chassis out and working on it. Even when the amp is unplugged from the wall, there are lethal voltages present until you drain the amp properly.

Lots of people on this board work on their own amps (myself included), but just know that it's not something to be taken lightly because you could literally kill yourself!

What Peavey is it by the way?
 
ITs a peavey Valve King. It is the head and its been a great amp head just ran into this problem at practice.
I do admit that i do not wait for the tubes to warm up for 5 min till i hit the standbye switch all the time. That may have taken affect what happened might of not. but i'm still trying to figure out if thats the problem the more i read on coupling caps the more i think thats what is wrong with the amp. because all my tubes do light up and my clean channel is a bit muddy with gain it seems.
Last question.
Should i still switch the lead pre amp tube with another 12ax7 pre amp tube to see what happens. and is there anyway to tell for sure if it is the coupling caps?
Again thanks
 
-Julian said:
ITs a peavey Valve King.
Click to expand...
Off topic here. If I could help I would. But I have a question.

What are your opinions on the valveking? Like what typ of music do you play, and does it really get a warm tube sound?

I'm just wondering for future reference when I want to get a tube head.

is there a setting where you can lower the wattage power? Like I know a bunch of heads have switches to switch to 50W or 30W.


Thanks for the info.
 
-Julian said:
ITs a peavey Valve King. It is the head and its been a great amp head just ran into this problem at practice.
I do admit that i do not wait for the tubes to warm up for 5 min till i hit the standbye switch all the time. That may have taken affect what happened might of not. but i'm still trying to figure out if thats the problem the more i read on coupling caps the more i think thats what is wrong with the amp. because all my tubes do light up and my clean channel is a bit muddy with gain it seems.
Last question.
Should i still switch the lead pre amp tube with another 12ax7 pre amp tube to see what happens. and is there anyway to tell for sure if it is the coupling caps?
Again thanks
Click to expand...

If I were you, I would try replacing the tube first. A cheap 12AX7 will run you under $10, and it's an easy fix. (Preamp tubes don't need to be biased.) If that fixes it, then you're done! (You can always upgrade to a better tube if you'd like.)

If not, then I'd look into the coupling caps next.

Amp repair isn't always a straight shot; there's some guess work involved sometimes.

To answer your last question, I don't know of any way to tell for sure that it's the coupling caps (aside from replacing them!), but someone else may be able to chime in with something else.
 
-Julian said:
Thanks guys appriciate the advice. Just one last quetion.
How do you double check to make sure the tube is out(it shouldn't light up right?) See i'm only guessing its the tube cause my clean channel is the only one that works and when i switch over to my lead channel i hear a big pop in the speakers and no sound.

THanks for all the adivice
Click to expand...

Is your amp a peavey valve king 50. If so here is a schematic I found:

http://www.blueguitar.org/new/schem/peavey/pv_valveking_112.pdf

Someone in the group might be a knowledgable tech who can look at the schematic and understand it all. My schematic reading skills are not much these days, but to me it looks as if the aX7s are staged in series as opposed to being in parallel channel circuits. e.g I don't see any "channels" per se, just two input connectors feeding the same first stage by different paths, and then switches and relays to modify signal path through a series of subsequent AX7 preamp stages. Thus switching the AX7s around isn't likely to tell you if one is bad. Your problem might be a tube or coupling cap, but it also might be on of the switches/relays, which have a higher failure rate due to moving parts.

Tom
 
unless ya just replace the caps to see if it helps(a process known as shotgunning parts), what you typicly find is that the voltage you expect to see at the input to the next section is higher than expected... so that requires either some experience or a well documented schemo to troubleshoot... what we are talking about here basicly is... the output of any of the tubes sits at a high percentage of the supply voltage in a DC sense.... the input of the next stage conversely is at a relitively low voltage DC wise... so these caps block the DC voltage and allow the AC portion (our sound) to pass.... makes sense???? do you feel comfortable with a multi-meter and high voltages???
 
Hey sorry, I haven't been on in a while, but i just wanted to thank everyone again, for all there advice, this forum seems to have people who know what there talking about subscribed to it... I'm going to try fixing it this weekend and if it gets done in time ill post what was wrong.
And to answer elenore

Its a peavey valvking 100w tube head and the sound that comes out of that thing is actually really good, especially for the price. Though alot does depend on what amp you use. I use a 1960vintage marshall and it sounds awesome but when i use my crate gt412 with it just doesnt get enough bottom end. But yea great buy. ...You cant adjust the wattage but there is a texture knob that allows you to change the sound from full to semi full like jazz/blues to metal which is pretty cool.
I play heavy rock.
 
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