Source: Musicians Hotline
Edition: February/March 2006
Article: Letís Ask Budda with Jeff Bober of Budda Amps
Q: I recently re-capped a friend's Silvertone model 1483 amp that had repeatedly blown fuses on him. After re-capping and turning on the amp I got a fairly loud hum that didn't change with the volume knob setting, and the 5Y3 tube seemed to get very hot. If left on for a couple of minutes the output transformer would start to smell and make a bubbling sound like hot oil. The power transformer voltages checked out as "good" (no load), so I'm wondering what might be causing the output transformer to overheat even without any signal being applied. I've tested the tubes with an old SECO tube tester, and they all get "good" readings. Would a bad output transformer make the rectifier tube overheat?
A: One word: yes. It sounds as if your output transformer has a short to ground somewhere on the primary side. That would cause the B+ (high) voltage to be pulled to ground through some degree of resistance in the transformer, causing a substantial increase in the amount of current being pulled through the rectifier tube. That, and the fact that the transformer "starts to smell and makes a bubbling sound like hot oil" are a pretty good indication that the output transformer needs to be replaced. You could try sourcing a replacement output transformer from the guys at Mercury magnetics (www.mercurymagnetics.com) I know they manufacturer some Silvertone "clone," but I'm not sure about that particular model. If not, you could always source a general replacement transformer for use the two 6L6s and an 8 ohm load. You should be able to find one at Mojo Musical Supply (www.mojotone.com) or New Sensor (www.newsensor.com). Since this is a relatively low-powered amp, you might even get away with using an output transformer for a Deluxe Reverb amp. It's likely that even that is physically larger than the stock transformer, but if you can fit it in, the amp will more than likely sound fuller and richer.
Like I always say, you can never have too much iron!
Until Next Time, Jeff Bober