Checked the fuse yet?
First knee-jerk thing to suggest is the filter capacitors in the high-voltage section. There should be a four-digit number on the filter capacitors, possibly preceded by a three-digit manufacturer's ID code in the format of "235-xxxx". Seeing the first three digits "235" would indicate caps made by Mallory. Might be a different three digits depending on the factory they came from. What we're really interested in are the following four digits. Typically two digits for the year, followed by two digits for the week of that year, 01-52.
So, caps marked "9225" would have been produced the 25th week of 1992.
Depending on mileage, they can go bad as soon as ten or fifteen years after they were made under heavy use, or might last for 25.
Might.
Tricky part is testing them. You didn't hear any "snap!" or "crack!" sorts of sound come from it, did you? That sound, along with a date code over 20 years old would suggest that it's time for a new set of filter caps. If one of these shows a short with continuity test, it's bad. But the chemistry inside can cause a short to "heal" and test okay with the low voltage from a meter. Typical behavior when a cap is just too old will be to break down when you power it up and apply normal voltage to the cap. You'll hear that "snap!" again if so. The entire set of eight caps should be replaced if one is bad. Changing just one of them will become a game of "electronic whack-a-mole" as the rest of them fail one or two at a time.
Or maybe you just had a defective fuse and the amplifier itself is perfectly okay. Sometime fuses just fail from wear and tear even when there is no fault to trip them.
It's not just the years, it's the miles too. If the amplifier saw a lot of regular use, the life of the filter caps tends to be shorter than if it was used say, once a week.
73
