MIMF

I am not familiar with all of the details of guitar amps.

Does some one have a site that gives good information about the various features?

Or is this a good item to create a FAQ?

Valve Wizard. When you out grow Merlin's web site, his books on guitar preamps and powersupplies take it farther. As a disclaimier, I was a proof reader for his books.

AX84 P1 and P1Ex theory documents do a good job of circuit analysis for a specific amp, and are deep enough to transport to other circuits.

AX84 for a high signal to noise ratio web community that is not tied to the past.

First off, are you interested in building one or buying one?
If you're interested in building one, there's two basic types, tube and solid state. There's lots of info on the web about designing and building both types, as well as hybrids that use both technologies. AX84.com is an excellent resource for tube amps, I've built the P1Ex kit and it was pretty easy.
If you're interested in buying one, you'll need to wait for someone up on the latest technology. It will help to know how you would be using it.

More interested in general knowledge rather than building one.

More interested in what features to look for when purchasing.

So subjective...all you really need are your ears.

There's too many options to make any kind of recommendation without knowing how you will be using it.
What will you be playing through it, and what size venue? Are you interested in onboard effects, or would you rather have stomp boxes?
Are you sure you really want a guitar amp, a bass amp or PA may better suit your needs. I'm guessing this is for the bass uke in another thread. Guitar amps are generally designed for overdriven tones, a bass amp or PA may be better for "clean" tone.

That is the kind of knowledge I lack.

I don't plan on "performing" as I only know about 3 songs.

But I do work on minor repairs and occasionally build an electric guitar.

As it is, I need something to check out the instruments a little.

To really trouble-shoot a guitar repair or a new build you probably just need something simple (perhaps with multiple impedance inputs for different pickups), don't need much power, and quite circuitry so you can pickup unwanted hums. Since you build basses as well, you probably would be better off with a small PA.

I understand the need to match impedance, but I don't understand multiple inputs for different pickups?

Well, depends on what type of pickups you'll be using with it.
Standard input impedance for passive magnetic pickups is 1meg ohm, and this is what you'll see on most every electric guitar or bass amp.
For unbuffered piezo pickups, the normal range is around 10meg ohm. Some "acoustic" guitar amp feature such a hiZ input.
For balanced microphone pickups, 600ohms is standard. Some "acoustic" guitar amps will have this type of input.

I've never seen an amp with all of these "standard" input impedances, but it's not uncommon to see higher end "acoustic" guitar amps with both 10meg and 600ohm inputs.

Other than the different input impedances, "acoustic", electric guitar and bass amps differ largely in their gain structure and frequency responses. None of them work particularly well in place of the others.

One option that would work if you're trying to find something to work in all scenarios is to use a mixer and PA (either power speaker or power mixer), and use preamps that are appropriate for the individual categories. Acoustic and bass amps don't rely too much on speaker and cabinet response, unlike electric guitar, so a preamp mated with a PA works quite well. For electric guitar, there are many affordable multi effects pedals that include speaker/cabinet modeling that works reasonably well, at least at lower volumes.
That's probably the way to go if you want the most flexible, compact and affordable option.

So you want a "testing" amp. Greg's reccomendations are right on, but could be a little pricey.
You don't need much power, 10 or 15 watts should be plenty, and a 10" or 12" speaker would be nice, an 8" usually doesn't handle bass very well, but may be OK for your needs.
For a single unit, my first choice would be an Ampeg BA-112. It has 2 different impedance inputs, it's not too big or heavy, and is really good for bass. It's also pretty good for clean tones on an electric guitar, and is not too bad for acoustic/electric. It may be more than you need, the small Fender and Marshall amps are also good choices. I regret selling my Ampegs, I've had a BA-115 and a BA-112. The 115 was too big and heavy, and I sold the 112 to buy a Vox T-60 to go with my Vox bass. (the Ampeg is a better amp) I also have a Fender Princeton 112(60 watts,12"speaker) , a Marshall 15DFX(15 watts, 8"speaker), a small Crate PA, and the homebuilt P1Extreame(6 to 18 watts, 12" speaker) so I'm pretty familiar with smaller amps. I haven't performed since the 70's, so I've lost touch with bigger amps.

There's loads of info on the net, from very basic to very advanced.
www.ampgarage.com is quite a civil place with a lot of knowledgeable people and a good atmosphere.
Although mainly focused on a couple of rarities of the guitar amp world, there's loads of info, beguinners guides, layouts to complete projects, etc. Check out the "technical discussions" corner....

Now I have had time to look at AX84.com....

I will come back in a few days after I have read some...

Hi Steve.....
sorry for the slightly false info.....
the thread " Reading material on steroids" is in the "Garage Talk" section....
Lots of links to tube and guitar amp related info....

Steve, while I highly recommend AX84.com, it's primarily geared to building tube amps.
If you decide to go that route, any of the basic designs will do what you want. I think I posted a build thread here when I finished my P1Extreame, but that's been several years ago. It ended up being close to $500, but that includes several different power tubes (it only uses one at a time).
I use my little Marshall for testing more than any of the others I have, and it's the cheapest amp I've got. $50 on craigslist.

I used to be a bit of a "gear head", especially when I was more active as a musician, and I still have some nice amps, including a Matchless DC-30 and a '66 Deluxe Reverb. However, in the shop, for testing guitars playing along with my favourite tunes on the stereo etc, I often "borrow" my son's little 5W Fender Champion 600. Yes, it is made in China, and the parts aren't high quality, and yes it is a one trick pony (in fact, there's only one knob...), but for low volume bluesy / jazzy tones, and a little bit of '60's classic rock, its not bad. I have a feeling Steve won't be playing loud metal or anything (but I could be wrong...?), in which case it would not fit the bill, of course. For $169,99 its a nice tube amp...

Hey, I have a '66 Deluxe Reverb too and I use it as my main gigging amp, it's the best.
The Epiphone Valve Jr. combo is a nice amp for the money too.

I've got an Ampeg reissue TremJetII. It's a bit on the pricey side (near $700 if I recall correctly), and is very simple with just volume, one tone knob, reverb and tremolo, but actually has two inputs for different impedance and has been a warrior for the last 10 years and is quite versatile (although probably more power than you need), but wouldn't handle a bass well. Old Fender Bassmans are fairly versatile as well.

Those are all nice tube amps, but you do pay a premium for the "tube tone", but that's only desireable for electric guitar.
I'd go for the solid stat Ampeg for those Ashbory basses & that bass uke without hesitation, but's that's my possibly outdated opinion.

I tend not to like guitar amps over 15W or bass amps less than 1000w but that might be because I'm a bass player? (Did the <g> tag get deprecated in phpbb3?)

Three songs is a good start but I think knowing a range of playing styles is really helpful for evaluations. The amp is really secondary once you know it's sound and gain.