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maddnotez 21st February 2011 08:17 PM

I think I blew my amp!! plase help
I have an older guitar amp.

Long story short. I used the pre of this amp into the power section of another.

However, I did not know what I was doing and did not use a dummy load.

The amp I used the power section from was fine. But now the amp I used the pre from is not working.

It turns on, but i dont get anything out of the speakers.

Anyone know what I did? Maybe I need a new transistor or something.

I dont know anything about amp repairs please help.

DF96 21st February 2011 09:12 PM

If the one which has blown was a valve amp then you may have damaged the output transformer. I'm afraid this may be expensive!

Running a valve amp at high level with no output load causes high voltages to develop which can break down the transformer insulation. The result is shorted turns in the primary winding.

maddnotez 21st February 2011 09:22 PM

Not sure.

Ill have to do some research since its an older amp.

The description says "All Tube"

Its a Crate Stealth 100w.

I got it cheap so unless its like $50 or less to fix im just gonna junk it.

M Gregg 21st February 2011 09:30 PM

Just for interest,

Crate 100 watt
Crate V-100h Head Died

Post #3

M. Gregg

M Gregg 21st February 2011 09:34 PM

Fuse 3 1A is the HT fuse.

This should be your first check!

Please be carefull Tube amps hold voltage at 400V and can kill you if you touch a live part!

If you are very lucky it's the fuse, just hope someone has not fitted an incorrect rating!

Fuse 3 is on the last schematic on page 2 of the PDF. It is in line with the HT to the Output transformer. This is not the mains fuse!

I guess its on the circuit board! Remember take care!

M. Gregg

maddnotez 21st February 2011 09:35 PM

Thanks for that thread M

sound similar.

Only it didnt cut out.

I actually fried my amp on my own doing. just not sure what went bad.

Thought maybe a couple of gurus here could point me in the right direction.

Truth be told i have another amp I use. This Crate is just sitting in my garage and either fix or trash scenario.

It would probably cost more to have a tech even look at it than id be willing to spend.

chrispenycate 21st February 2011 09:38 PM

Was the older amp you used the preamp from a valve (tube) or transistor output stage? (mostly the tube ones have ventilation grills you can peer through and see things like jamjars glowing inside, and will produce a lot of heat. Or tell us what model of amp it is.)

Stage amps using transistors should not get upset about driving open circuits (= nothing plugged into the output), so the problem is most likely signal not getting where it's supposed to be. The reason tube amps get unhappy is the output transformers, which tend to ring on transients when undamped.( a bit like one of the joke hand held electroshockers). As this can produce fifteen or twenty thousand volts on bits of circuitry designed to take four hundred and fifty, octal bases can arc over, transformer windings fry, output tubes produce their own light shows; not the best first job for a neophyte repair experience.

However, the indicator light comes on, and the preamp stage was still working as long as you tried it, so you've not blown the mains fuse, and probably not the HT, which most of the more extreme damage would have done. Good sign. and I assume it wasn't making any fizzy, crackley noises from inside the electronics, or smelling of burnt bakelite, or you'd have mentioned that.

What do you have available as test gear? Even a nasty little multimeter would be a help.


maddnotez 21st February 2011 09:41 PM

The subject amp is a Crate Stealth 100w.

I took the PRE from the crate into Power of Peavey 6505+ 120W

Did not use dummy load. Fried the Crate but the Peavey was fine.

There was a little flubber if you will at first from the crate. Like you could barely barely hear guitar notes coming from the amp its self not the speaker cab.

Nothing at all coming out of speaker cab.

Amp turns on fine power indicators are good. Just no sound.

I have an OHMeter?? lol

M Gregg 21st February 2011 09:44 PM

Best of luck.

Catch you later!

M. Gregg

century tek 21st February 2011 10:25 PM

From what you have described as sounds coming from the Crate amp and not the speaker itself, an output transformer will "sing" if you will, with no load (speaker) connected to it, so its quite possible you fried the output transformer. As noted above, A short occured in a winding from having no load.

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