I have a Crate v32 1X12 guitar amp, the volume cuts out and then begins to feed back. To make a very long story short the tubes are good (I KNOW the tubes are good!!!) it is not the cords pedals etc. any ideas??

Turn your guitar away from the amp's speakers. The pickups on the guitar are feeding the amp's signal back into the amp creating a feedback loop, especially with the gain button on. Loud volumes cause this looping path between the amp speakers and guitar pickups. You may need to reduce amp volume also.

then the problen is in the power amp section after the preamp stage. Contact Crate for your nearest service center.
http://www.crateamps.com/support/index.php

Contact Crate for the best info.
http://www.crateamps.com/support/index.php

Perhaps you have a bad capacitor on your volume control?

You can get an ESR meter and test your exposed isolation caps for leakage? The have to be removed so unplug the unit if you are gonna do any work inside the cabinet.

Also, try a shorter or higher quality guitar cable. This will cut impedance between the pickups and the amp.

Good luck and be careful!

You can reach the limiting IRRESPECTIVE of where the volume control is set when you have a guitar or other source that has HIGH output.

Guitars that have battery in them with internal amplifiers are an example of a high output guitar. Plain inductive pickups may require the volume control to be set at say 70% to reach limiting.

Please NOTE that the volume control is NOT linear, but is an "audio taper".

Limiting means you are probably driving it too hard. Many learn the hard way when speakers and thee power amp fail.

When the cone is driven too far beyond the pole pieces of the magnet, then the IMPEDANCE of the speaker becomes relatively low and can damage the power amp. The limiter tries to prevent this by sensing the current and or voltage and will back off the gain internally. This causes distortion when it happens.

Not good. If you have electronics experience, you can replace the power amp IC to fix it.
Paul

Start easy. You could have a bad power switch. Do you get any kind of indication of any life at all, like tube filiments or front panel indicators? If the fuse is blown you have a fault that is drawing excess current, in which case you can check the rectifiers that create your bias voltages, yank the output tubes to see if they have an internal short, less likely would be a shorted filter capacitor (although I have seen it). You could also have a bias problem on the output tubes that causes them to draw excess current and likely makes the tube(s) glow bright red before popping the fuse. If this is the case, look for shorted or leaky coupling capacitors and burned bias resistors, or maybe just a tube with internal shorts, and you will likely have junk tubes as a bonus (they don't take kindly to glowing bright red- meaning a glow that is far more intense than the soft glow of the filiments). If the fix gets more involved than all of this, give me your email addy and we can get hard core.

Their may be a schematic on the inside of the amp.I don't remember if Crate puts one or not. And I have had several Crate amps. never needed repair except for tube replacement. If there is not one in side , go here and find what you need . http://www.crateamps.com/support/warranty/ Good luck DFD please rate me TK U

Your amplifier is a solid-state rectified tube amplifier. This means that a tube is NOT used for the power supply. Why is this significant? Because most of the time you have the problem you are describing, it is because of the tube rectifier.
Since this amp does not have a tube rectifier, the problem is likely one or more of the tubes. I have seen in 95% of the amps I repaired that the tubes were the cause, and since the amp is so new, I would suspect tubes first.
Now the hard part: which tube? Without a tube tester, you will have to use the 'firewall' technique. You will need to get a bunch of replacement fuses, as you might go through a few untill you find the problem. Radio Shack is a great place for fuses (make sure they are SLOW BLOW type).
The problem is almost guarenteed to be the power tubes: they are a big failure mode in tube amps (the preamp tubes are not as likely the problem).

This is what I do at a customer site without a tube tester:
(1) Have either a KNOWN TO BE GOOD REPLACEMENT SET OF TUBES or a NEW SET OF TUBES.
(2) Have plenty of fuses.
(3) Start with power tubes: they cause most of these problems. Replace burned out fuse.
(4) Replace all 2 (or 4 in your case) with the good tubes.
(5) Turn on amp and play on it (30 minutes at various volumes and settings). Turn it on and off many times using the on/off procedure your amp requires (like using the standby switch on some models).

* if the amp plays and works, likely you had a bad power tube. If you are blowing fuses, the problem is either the power amp circuitry or the preamp tubes.

* Leave the good power tubes in before going on to the next step. Also: the minor difference in bias wont matter for what we are doing now: the bias being WAY out is almost never the cause.

(6) Check preamp tubes (easy to do, as this does not require us to poke around on the insides).
(7) Replace burned out fuse (atleast number two by this point).
(8) Replace all preamp tubes.
(9) Turn on and repeat step 5.

* Blowing fuses at this point means atleast two types of repairs needed: retention tube sockets or someone to look inside the amp. Either way, this is a serviceman repair (things I do). Since the amp is so new, take the warentee buyout and throw it back to where you got it. Crate is real good about dealing with these issues (if you are the only owner and it is within warantee).

If you need to contact warantee support, you can tell them you have had the amp re-tubed and the problem still persists (meaning they can brush you off with 'just get it retubed and then call us if there is problems'. This is like 'take two asprins and call me in the morning: 95% of all tube amp problems can be fixed by this (retube, not asprins).

If you have to do the warantee route, KEEP YOUR NEW TUBES. The preamp tubes are fine, but the power tubes may be damaged. Wait for what Crate tells you before you use them. This is if you are cheap. I would pitch all of the tubes and consider the 70 bucks as my cheap attempt to bet I am in the 95% solution number (tubes are the cause). Otherwise, the repair will cost shipping at a minumum. Dont you love it: tube amps are expensive and require someone with deep pockets to enjoy the tone. But what can we do: tubes DO sound better and when everything is working, they perform reasonably well.

Good luck on this!
-mike

Yes.
Are you saying that the only indication that it is running at all is that the fans are running? So the tubes don't light up? No indicators on the front of the amp?
Power supplies that provide multiple voltages, which your amp has, can provide some of the voltages while having a problem that prevents them from providing others, all while not blowing a fuse. If you are not confident in your ability to work on a piece of electronic equipment that has 120VAC coming in and at least 175VDC or more present inside it, bring it to a service center.
The good news is that it is probably not horribly serious. Problems like this can almost always be repaired in a cost effective manner.