Lots of questions... I'm New

[dpanita]

I have a crate vc3112 that I think may need all of the tubes replaced. One of the tubes ( in a canister-like object with a spring) for sure is burned. Is this power amp tube or a pre-amp tube? I'm guessing that the this one in the cannister is a preamp tube because its near the input, and the input is not working at all (my whole reason for exploring this electronic wonder).

I understand that Sovtek 12AX7A's and EL84's are stock in this amp, But I don't know which is the pre and which is the power.

I also don't what replacement tubes would improve my amp, where to buy these replacements, or if the bias would need to be reset to be compatible with these new tubes installed. I've read conflicting points on the bias issue. One person says the bias adjusts automatically in this particular amp, another says it needs to be set manually. If it is manual, is this process too involved for a wanna-be novice, such as myself? for that matter is physically installing the tubes difficult? I am interested enough in learning this subject and saving some cash to completely ruin this amp by "fixing it" on my own.
Any help would be greatly appreciated.
Thanks,
Nick

[oc disorder]

I'm relatively new here too but I'll attempt to answer some of your questions.
According to the schematic on Blue Guitar org the Crate VC3112 uses cathode
bias (same as Vox AC 30 only different values) the schematic is under
"Misc Amp Schematics" so therefore was not intended to be adjusted.
That means you can just "plug 'em in". This refers to the output valves EL 84.
You can just plug in preamp valves as there is no adjustment required .

When you say the valve appears burned there is allways a silvery/darkish
burn mark at the top of the valve. This is part of the manufacture process
look up Flashing (not the x rated sort) and Getter...
see http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm

If the top of the suspect tube has gone white most likely it is no longer
a vacuum so needs to be replaced.

The metal cannister as well as keeping the tube in place acts as a shield
and helps prevent hum pick up ,its usually refered to as a shield.

If you look at the valve when you turn the amp on you should see its
heaters (like filaments in a light bulb) glowing you may have to do this in a darkened room .

Usually if the vacuum is gone the heaters burn out.

Mesa Boogie handbooks have a good analogy on how valves work too,
not sure if its on their site or you have to buy one to find out !
As I recall it's got to do with saloon bars and bar maids dunno what thats got to do with rock and roll but I digresss...

Its a bit of a learning curve to jump in on a valve amp to learn electronics
crystal sets,buzzers switches lights is more the initial background but you
gradually pick up things and accumulate knowledge.

I noticed on the schematic it has a tip,ring sleeve effects loop this is a point
between the pre amp and the power amp. If you plug in to this you should
hear a faint sound but it wont be very loud as it hasnt been "pre amplified".

These Effect loops have a kinda switch built in so when you are not using
it the pre amp is normally conected to the power amplifier.

So if the "switch " in the socket is dirty or faulty no sound will get through.

It uses what is known as a T.R.S. jack (tip ring and sleeve) like on a stereo
headphone ..in this case the sound coming out (send) and the sound going back in (return) can be handled by one socket ..only have to drill one hole !

Hope thats a good start for you there are many illustrious informed intelligent
characters on this forum whom I'm sure can enlighten you further.

[Enzo]

Um... is there a problem with the amp? You don't mention any issues other than the way the tubes look.

It is hard to tell a bad tube by looking. As OC said, the black silvery stuff on the glass is normal - it is a result of what they do to get the last bit of air out of the tube. If that turns white, then air is in the tube.

If you see lightning inside the tube, it is bad.

If you see loose bits of stuff rolling around in the tube, it is bad.

Otherwise, can't tell by looking.

Does the amp work?

The larger EL84s are the power tubes. the smaller 12AX7s are the preamp tubes.

people chant "bias bias bias" like a mantra without knowing what it means or what it does or where it is and is not. This amp is cathode biased and has no adjustment. Next time someone insists it absolutely MUST be "biased," show them the schematic and ask them to point out the adjustment control. Then go have lunch while they struggle with that.

Depending on your style of play - and I don't mean blues or jazz, though I guesss it is related - different brands of tubes will have a relatively subtle difference on tone. I think it is about the same diference as different brands of strings on your guitar. You can hear it but it is not a lot.


Power tubes wear out just doing their job. Like tires on your car. Preamp tubes tend to work a long time. I only replace them when they fail. LIke wheel rims on your car.

When power tubes wear out, they act similar to strings. They keep working, but they have lost their tone, their sparkle. Worn strings sound dull. Worn power tubes sound dull, not unlike the sound of dead strings.

[dpanita]

That's great stuff guys! Thanks!
I am able to see the one preamp valve is not glowing.
I gather from your concurring comments that this is a repair I can probably do myself without worrying with the bias issue.
I bought the amp in '96. So I'm guessing that after ten years that all the tubes need to be replaced.
What tubes do I buy? any recommendations? Is the tubestore.com ok.?
Thank you guys. very helpful.
Nick

[oc disorder]

Some 12AX7 reviews here = http://store.tubedepot.com/12ax7reviews.html
A lot of new amps come with Sovtek 12AX7WA's fitted.
They seem to be reliable and a economical rugged work horse.
There are several different brands to chose from .
The ElectroHarmonix valves (made in the same factory) are also popular.
If the amp is "oldish" and you have never changed the valves and it has been used a lot it may be good insurance (if you can afford it) to change the
EL84's before they start causing trouble. I have heard the EH EL84's are
more rugged than their brothers the Sovtek EL34's but I have not verified this. There are lots of opinions out there on forums about various valves,
some of which is dubious at least. I think the majority of tone comes from the fingers and the expression of the guitarist, the rest is just the icing....!

[Ptron]

dpanita, you still didn't say what the problem was with the amp other than it looks like one of the tube's heater isn't lighting. Does the amp work? Are you sure the heater's not lighting in that tube? It can be difficult to see sometimes, and if the tube shield is on you may not be able to see at all. Take the tube shield off, turn the lights out, then look. If it truely is out try, switching places with another 12ax7 (if there is one) to see if it's the tube or the socket/wiring.

[dpanita]

The amp works, except for when i'm plugged into the input...I've actually been plugging the effects pedal into the effects loop on the amp for practice purposes. The reason i thought for sure the tube is the problem is because it appeared not to be lighted. after I turned off the lights it appears that heater is working.......at least sometimes....just like the volume cuts out sometimes...
Maybe i should change the input first??????

[dpanita]

Amp is working.......kinda

The amp works, except for when i'm plugged into the input...I've actually been plugging the effects pedal into the effects loop on the amp for practice purposes. The reason i thought for sure the tube is the problem is because it appeared not to be lighted. after I turned off the lights it appears that heater is working.......at least sometimes....just like the volume cuts out sometimes...
Maybe i should change the input first??????

[dpanita]

Switched tubes around......

I swapped one of the pre-amp tubes for another and had the same exact results. The tube that I repositioned had exactly the same results as the respective previous tube.
Which is indicative of what? My guesses are..

1.The socket is bad.....? The glow is visible sometimes from this particular valve.
I have to tap the back of the valve at its connection with the board..(socket?) to get some results. (results= the valve glows and normal sound through the speaker) However this tapping occurs near the input's position on the board as well, so maybe...

2.The input is bad.....? I do not know how to remove this input from the board without breaking it. The input itself still seems tight enough to work though, so maybe......

3.The connection between the input and the socket is bad on the board..If this is the case can it be fixed? This connection is between the back of the board and the board encasement. Which means removing all the knobs,etc......arrgh

Any hope or suggestions....
Don't forget This amp was built in 95 so the electronics are somewhat advanced and more flimsy.