Tube replacement questions from a beginner...

I'll take a crack at this.... Not an expert but I do have some experience here and I'll just throw some stuff out for you to chew on.

If I understand your question... there aren't different versions of 12AX7 for preamp vs. poweramp positions. A 12AX7 is a 12AX7.
Now, as it happens (and just to cloud the issue a bit) I have a small 1w amp that uses a 12AX7 as it's poweramp tube, but that's a novel and unusal way to use a preamp tube, as I understand it. Which brings us back to the point, which is that a 12AX7 IS a PREAMP tube, not a power tube.

Which makes me wonder if you're a bit confused as to which tube is which - a 12AX7 is a PREAMP tube while I believe that an EL84 is a POWER tube.

The 12AX7 is a member of a "famly" of preamp tubes that are somewhat interchangable. The 12AX7 has the highest gain; there's also a 12AY7, a 12AU7 and a 12AT7; each has a different level of gain, and people often swap these tubes around to tweak the output of an amp.

There are different manufacturers of tubes, some are considered "better" than others, but also, different uses for different tubes lead to different quality issues. For example, 12AT7's are often used in a certain position in things like reverb circuits where sound quality doesn't really matter so if you buy a 12AT7 and stick it in your preamp position (like I did) you might find that it's a little bit microphonic (i.e. when you bump the floor next to the amp it goes "bwiiiiiiiiiiiiiiiiiiinnnnnnng").

My 5E3 amp can use either a 12AX7 or a 12AY7 as it's preamp. It acutally uses 2 12A-7 tubes - one as the preamp and the second as the rectifier. I leave a 12AX7 in the rectifier position but swap between 12AX7 and 12AY7 in the preamp position. The X gives more gain which equals earlier breakup (i.e. blues grind tone at lower input level) where the Y gives a little later breakup (i.e. a cleaner tone). Generally this sort of swapping (12AX7 and 12AY7) is what people do with these preamp tubes.

A lot of reproductions of amps that were originally designed to use 12AY7's (like the 5E3 - the Fender Tweed Deluxe) have been made for a while using 12AX7's as the default because for a while 12AY7's weren't being manufactured.

Power amp tubes are a different story. For the most part you've got to stick with what's the amp was intended for. There are some exceptions but I don't really know the details and generally I think that the best advice is to not do it. The power stage of an amp is where the big voltage lives and up there little changes have bigger consequences. There are specific amp mods that people do to make specific kinds of amps take specific tubes that they weren't really designed for but this work is a little dangerous if you don't know what you're doing and requires an understanding of amplifier design. Generally, substitutinging power amp tube typess in an amp will result in you seeing smoke come out of the amp. And as everyone knows, electronic equipment actually runs on smoke and if the smoke gets out the equipment stops working.

As for manufacturers of tubes, JJ Tesla's are supposed to be great; I've been using Electro Harmonix tubes and like them fine. Tube afficianados will go on forever about different tubes having different characteristics and they really do know what they're talking about but if your amp sounds good and isn't microphonic, be happy and play with it for a year so you really know what it sounds like before you go bothering to change tubes; then try swapping brands to see what changes.

Re things to watch out for.... Change 'em when they're cool so you don't burn your fingers. Don't touch any wires 'cause there can be lightining in there even when your amp is powered off an unplugged (i.e. until you know what you're doing don't open up the back of the amp). Don't ever run your tube amp with the speaker not hooked up or with a tube missing. Make sure the pins are lined up so you don't damage the tube and don't force anything. Make sure you're putting the right tubes in the right sockets.

Enjoy. Tubes are just plain cool.

Congratulations on the new amp. :D

First, if you just got this amp, why do you want to change the tubes already?

Second, the ECC83/12AX7 is the preamp tube, the 6BQ5/EL84 is the power tube. The ECC83/12AX7 is a short stubby tube, the 6BQ5/EL84 is longer and narrow. Plus, the tubes should clearly be marked. So there is no problem telling them apart from one another.

Yes, they have to go in the proper position. You can not switch the tubes positions with each other. I don't know what would happen if you switched their positions, but it probably wouldn't be good for your amp.

Tubes are very easy to change if you take reasonable care. Of course you want to be very careful not to electrocute yourself. I always work with one hand and keep the other hand in my back pocket, a trick my father taught me (electronic technician by trade). This will prevent electric current from passing through the heart. If you are not experienced in this area it is probably best to pay a professional to change the tubes.

So proceed at your own risk.

Tubes pull straight out. Sometimes a tube will have a clip that secures the tube and also prevents the tubes from rattling and shaking. Sometimes you have to spread the clips to pull the tube out. Never use a lot of force to remove the tube. If it seems to be stuck, give the tube a little side to side wiggle (just a little). You do not want to bend or break the pins on the tube.

Look at the pin pattern and make sure the new tubes are aligned properly with the socket.

Push the new tube in. That's it. :D

There are some tubes you can substitute one type for another, and some you can't.

There are lots of places to get tubes. I like JJs from Eurotubes. They are good tubes and the prices are great. Go to the site and read. There are articles on various tubes and substitutions. You can also e-mail Bob the owner, he is very helpful in answering questions.

Eurotubes

Once again, if you have no experience with electronics, you should pay a professional to do this work.

Wes,
He's in Germany. I don't know if BOB does International orders or not..?!?!

I agree with Wes and would like to re-iterate.. if you don't completely understand what your doing to Re-Bias etc... Have someone else do it.. if you touch the wrong part on the inside of your amp....it could kill you....even though the amp is unplugged and to make it worse,

you RE-BIAS with a fully powered up...ON...Humming amp...

Good luck and congrats on your new Amp.

The 12AX7 is the pre-amp tube. The El84 is the power tube, as has already been said. Unless I'm mistaken the 12AX7 has 8 pins and the 6L6 has 9. The 12AX7, though, is NOT a used as a rectifier, that is a special tube, originally a 5Y3 and later a 6X4.

Before removing any tubes, mark the chassis next to the socket with the tube's number.

Other than that, follow Wes's advice.

Unfortunately, I found out that some tube makers advertise high quality tubes, but their products are inferior.
It's advertising, and nothing more.

Also, some people are advertising tubes at extraordinarily high prices, espicially military spec tubes.
I'm very lucky to have a tube amp builder in town that is very friendly and set me up with a great set of 6L6's.
His price was something like $50 or so, and he showed me a magazine ad that listed the same tubes for $250!
He had matched them by comparing that bias currents - its a simple matching technique.

My second choice would be Groove Tubes. Aspen Pittman wrote the book on tube amps.

Ron

PS
I purposefully didn't mention the name of the tube manufacturer. They make great amps.
Their "matched" set tubes, however, are of very low quality.

Yeah, on that 12AX7 "rectifier," I think the term you're looking for is "phase inverter."

I'm kinda old fashioned and out of step with the heavily tube-salesmen-influenced guitarists of today, but I don't replace a tube till it's not doing its job right and I also don't believe that there are certain brands of tubes that have "The Sound" while others don't.

Thank you so much for taking the time to answer my question, I appreciate it.

Things are a lot clearer now!
You know perhaps I got confused with the power and preamp tubes, but this is what stands right in the manual...

"The preamp and power stage signal paths are both 100% tube. The combination of a single ECC83/12AX7A based power amp and a single 6BQ5/EL84 based preamp yields 5 watts RMS output."

I'm not planning to change the tubes any time soon, it was just a general question I never thought about since it wasn't necessary.
If it's time to replace anything I'll probably go and take it to the shop where I got it.

Thanks again!

You might find this page interesting
http://www.angelfire.com/blues/rockinjohn/skylark_ga_5.html

Yeah, on that 12AX7 "rectifier," I think the term you're looking for is "phase inverter."

Yup. Caught me.

Different tubes do sound a little different, but often you do not get the dramatic effect some people expect.

As far as recommending JJs, I had originally read where some customers were very happy with the improvements these tubes made to the drive channels on the Hot Rod Deluxe. I liked my HRD stock, but the Drive channels were a little boomy and muddy. I wanted spare tubes anyway because I gig, so I took a chance on these tubes. The prices were very good as well.

And these ECC83Ss really did improve the Drive channel on my HRD. They also rolled off just a little of the highs as well. My HRD could be ice-pick piercing. So I liked this too.

But I am in no way saying these are the greatest tubes out there. I wouldn't have any way of knowing, I have only experimented with a few makes of tubes. But they were good, the price was right, and the service was great. So I would recommend Eurotubes to anyone looking for tubes.

I also fully retubed my Marshall DSL401 with JJs. I am even happier with the improvement these tubes made to my Marshall than my Fender. My clean channel is far louder and absolutely beautiful tone now. I cannot say enough how pleased I am with that. The overdrive channels sound really good too. Very thick and full sounding.

I also changed the speaker in my HRD just for experimentation. I put in a Celestion G12T-75, the speaker Marshall uses in many of it's cabs. I was looking to get more big bass, but controlled, out of my HRD. And it really seems to have worked. The amp has a little more of a Rock tone now as opposed to Blues. I have really been happy with this speaker. I have thought of trying a Vintage 30 as well, they are a great and famous speaker.

But changing the speaker had a far more dramatic change than tubes.

I also have to admit that I just plain like experimenting with my amp. It is fun to swap tubes and speakers and listen to the results. :D

How difficult is a speaker swap. I'm looking to get more piercing tone out of my epiphone, and a bit less muddy.

How difficult is a speaker swap. I'm looking to get more piercing tone out of my epiphone, and a bit less muddy.
95% of that job is getting the old speaker out and the new one in. How easy that is, is determined by the construction of the housing and the amp chassis. This pic will give you some idea of the problems, you're likely to face:

As you can see, the speakers are situated behind the chassis - to get them out, you need to take the chassis out (otherwise you have no access to the screws at the top of the speaker.
As far as I can tell, the Epi Valve Junior is very similar.

You may also be unlucky and have a new speaker that has screw-holes set differently to the old speaker.
Apart from those problems, the speaker only has two connections to desolder and resolder.

And sometimes the wires are attached with slip-on terminals, no soldering necessary. A nut driver of the appropriate size is just about a must to get the nuts on and off of the speaker mounting bolts.

For sure, speakers make a far bigger tonal difference than tubes. Or pickups.

Yes, it is hard to say how difficult it would be to swap speakers in your amp without seeing it.

On my HRD it was really pretty easy. I removed the six screws that held the head and pulled it out. This gave me clear access to the speaker which was held in by four screws. The speaker terminals were clip on, I did have a little trouble pulling one off. But the old speaker came right out, and the new Celestion fit perfectly. Took seconds.

But then the hard part...

I did have a little trouble getting the head back in. It was an extremely tight fit. There was shielding tape on the inside of the cab, some of this tore and doubled back. Took a minute or two, but I got the head back in and was able to push the tape pretty much back where it had been. But if I sent my amp in under warranty they would know I was in there because of the torn tape. I used a long punch to line up the chassis with the screw holes in the cab, put the screws back.

Took me about 30 minutes total. But I went real slow. Other than the super tight fit of the head, it was really easy. I'd do it again no problem.