Inside, there was the typical 70's fender tag strip with one of the legs of the incoming mains coupled to the chassis with the blue radial cap. Apparently, fender installed what appears to be a thermal fuse in some other/later models.
It has a UL sticker on the back panel as well. I double checked on the schematic and confirmed that it was designed and built without one, which is crazy to me.
I mean, there was no mains fuse at all, and there never was in this amp!!. Not like, the fuse was missing from the fuse holder. So, after replacing the mains power cord with a new molded plug, I went to check the fuse and. One of the other routine checks I make, particularly in vintage amps, is confirming the fuse value and rating is the one specified. More often than not, it's a disaster and it gets replaced–as this one did. We see this a lot, and I always check the condition and wiring inside. The molded plug end had been replaced by an old 3-prong replacement with screw terminals. But the amps still got UL certified.We had a 70's Musicmaster Bass amp that came in for general cleaning/service (dates to '79, it looks like). In some older Fender amps, the presence pot actually can have a low dc voltage on it - I mean the pot itself. So I think in practice, the only significant risk is that they break eventually, if wired according to regulations. And finally, they have to pass stringent official tests to be able to be used in this application in a production amp like a Fender. They are made as separate units, which then get attached mechanically to the volume pot, and which will have thick plastic sides, thicker than any high voltage wire in the amp. They should be wired only to the neutral side of the mains, which theoretically is at zero volts, or near that - what the switch does is just complete the 'on' circuit. As was mentioned earlier, this is a bit of a safety concern.I'm not crazy about them myself- but I think it's intuitive, rather than rational. I myself, am not wild about on and off switches for high voltage circuits being from the volume knob. As was mentioned earlier, this is a bit of a safety concern.ģ. Be prepared to do some searching for replacements, and if you want NOS, spending even more than what used sweep tubes normally go for.ģ. So replacements are more difficult to find than 6L6s, 6V6s, E元4/6CA7s, etc., and can be pretty expensive (a few years ago, I spent over $90 for a pair of USED 6KD6s, that looked, to be in OK shape, so I'd have a set up backup final/power tubes for a 46 year old Yaesu FTdx-401b ham radio I have, that puts out about 300 watts of power). Unfortunately, ALL sweep tubes are extinct nowadays - they haven't been made in decades.
FENDER MUSICMASTER BASS AMPLIFIER TV
Sweep tubes were originally developed to help run the sweep circuits for TV picture tubes, but were discovered to work fine as power tubes (with certain restrictions needing to be kept in mind - they don't tolerate being out of resonance/tune in radio application ), and due to their low cost (you used be able to pick up replacements cheeep at your neighborhood drugstore), were used in some amplifier circuits.
Oh yeah, and don't expect super loud - the amps put out 12 watts of power.Ģ As was mentioned, the earlier versions of the Musicmaster Bass amp use 6AQ5 tubes. In a way, they're almost like a poor man's Tweed Bassman. They can get pretty dirty sounding, when turned up. If you want squeaky clean sound, a Musicmaster Bass amp isn't for you.