Champ problems

porge · Post by **porge** » Wed Jan 24, 2007 7:14 pm

HEy Guys, I have TWO silverface champs that have done the same thing.

I bought one off eBay that had an Altec driver, which sounded OK, but was 8 Ohms, so figured I'd swap it out for a cheap Jensen MOD 4 ohm. When I powered it back up after sticking the speaker in, the pilot light flashed on, then off, and now nothing...zip. THere was no smoke, and the fuse is OK. Tried switching 5Y3's, nothing (the 5Y3 I got with it was a boxed, NOS Sylvania). I tried the tubes out of my vibrochamp (which operates). Nothing.

Have I blown the PT? THere is no telltale wax leakage.

Thanks in advance!

triode · Post by **triode** » Mon Jan 29, 2007 6:49 pm

You may have a blown power trans. Do you have a voltmeter? If so, plug the amp in and measure the AC voltage between the two yellow leads going to the 5Y3GT socket. If you get 0 volts you need a new power. They are available cheap from Antique Electronic Supply, MOJO Music Supply, etc.

doctorwho · Post by **doctorwho** » Tue Jan 30, 2007 1:56 pm

Charlie, could one conclude that the amps then should have an 8 ohm load, being that both amps blew the PT when a 4 ohm load was put in?

porge · Post by **porge** » Tue Jan 30, 2007 2:01 pm

Champs are designed for a 4 ohm load, and this one does have it's original OT, so I'd be doubtful.

If PT is toasted, I'm guessing it's a coincidence. Speaker is fine in all my other champs.

soundmasterg · Post by **soundmasterg** » Tue Jan 30, 2007 4:26 pm

When you plug in the amp and switch it on, do the heaters light up inside the tubes? The heater winding on the power transformer could have failed, or something along the heater wire string iside the amp could have come loose or disconnected. If you know enough to work on amps yourself from a safety standpoint, then open the amp up and turn it on and measure the heater winding from one side to the other. You should get 6.3v or thereabouts. If you don't then the heater winding could be dead on the PT in which case you would have to replace the PT or have it rewound. There is acutally a 6.3v heater winding, and a 5v heater winding for the 5Y3, so eithe rone could have failed. If you don't know the safety aspects of working on a high voltage amp, then take it to a tech so you won't hurt/kill yourself.

I don't think the problem with the amp has anything to do with the 8 ohm speaker being in there...Fender output transformers can usually handle a load mismatch pretty well. Also, you only see wax leakage when a power transformer gets really hot, so if it blew before it got hot, then you would not see it. You CAN check the power transformer another way to see if it is good or not, but it is only really valid if it is blowing the fuse. If it doesn't blow the fuse, then it isn't much help. To do this test, you disconnect all secondary leads of the power transformer from where they are wired inside the amp, and make sure they will not touch anything. Then you turn the amp on and see if it still blows the fuse. Since the fuse isn't blowing in your situation, then personally I think the power transformer is still ok and it must be something else like the heaters.

porge · Post by **porge** » Tue Jan 30, 2007 4:46 pm

Thanks for the reply Greg - as always, a well informed one!

When I didn't get the pilot light, I switched it off quick, so haven't looked to see if heaters are heating. Will check tonight.

I know enough about them to keep it safe and keep it simple (years of working on computer monitors teaches you to respect the insides of most equipment).

As a precuation when doing my "work" on my stable of champs - mostly rewiring them to 240V operations - I check the voltage in the "hot" side of the capacitor can to check if safe(well..safe-ish) to work on. When this champ first exhibited this, I checked voltage and remember it being substantial - 300V+ or so. Don't know if this helps....

soundmasterg · Post by **soundmasterg** » Wed Jan 31, 2007 12:10 pm

The 300v on the cap doesn't mean anything except that you have to be careful, because a cap can keep a voltage on it for a long time without more power being applied. You really need to fire it up and check voltages, of course making sure that no tubes are red plating or fuses are blowing. Check the heater voltage. Check the rectifier tube voltage. Check the power tube plate voltage. One or more of these will probably be incorrect and should point you in a direction to troubleshoot.

porge · Post by **porge** » Wed Jan 31, 2007 4:27 pm

Thanks Greg,

Will check further tonight.

Another one of the champs seems to have a lot lower output at the moment...like running around 20% of power...any clues? Tubes are known good'uns, speaker the same.