broken amp question

[PallarAndersVisa]

Got a broken 5150, owner doesn't know whats wrong with it.

I replaced a couple blown fuses inside (5 fuses inside this thing!) and replaced all the power tubes. Pre amp tubes look fine so I don't change em.

Now the amp powers on and I get the green light, but there is barely any sound coming out of this thing. Like I have to crank the master (post gain) half way to hear anything. Sounds like its coming out of a broken AM Radio.

nothing else on the board looks blown. Any idea what might be causing this?

[Rsmacker]

I'll give you a tip, keep your mitts out of it and give it to an expert. Poking about in valve amplifiers, when you don't know what you are doing, is a seriously dangerous trick, even if it's switched off. There's a reason those fuses blew, which ones were they? What was the owner doing to it when it stopped working?

Not trying to be flippant, but there's probably something on there that says "No User Serviceable Parts Inside". Seriously, tread very carefully...

[straycat]

Change the power tubes with some spares and see what happens.Two blown fuses huh? has to be a reason don't go poking around take it to an expert.

[JACKSONFREAK]

Those caps hold a charge for a long time and can give u the worste shock of ur life. It can kill u. Could be cracked tube sockets or a bad transformer. Anything. Take it to a qualified tech.

[Hellbat]

If you don't want to spring for a full set of pre-amp tubes, try buying 1 new 12ax7 and test it through the different tube sockets to see if one of them is the culprit. After that, I'd have it looked at by a tech.

[DonP]

nothing else on the board looks blown. Any idea what might be causing this?

A possibly very expensive output tranny might be blown.

[Spivonious]

I'd say preamp tubes or a burned up component on the board (capacitor most likely). I had the same symptoms in my Genz Benz El Diablo and it turned out to be bad capacitors burning up the screen resistors.

If new preamp tubes don't fix it, I'd check each component on the board. Make sure resistors match their spec and make sure caps have good connections and aren't bulging or leaking.

If you turn the amp off, unplug it, and then turn the power switches back on, it should drain the capacitors. But I'd still be very careful when poking around. Caps can hold lethal current and love to discharge through your body.

[rdamaral]

This is very close to what happened on my JCM 800. It was bad caps. If you don't know what you are doing, please take it to a tech. Very lethal doses inside.