Slightly OT: What Did I Just Do???

[Shane]

I was just wondering if someone could explain (electronically) how I managed to blow out my amplifier this evening. I have a Newcomb tube-powered 1950's classroom record player, great for playing 78s. I figured I would run a cord out of the "headphone/speaker" jack, turn the volume low, change the solitary mono signal into dual channel mono, and run it into my 1970s Pioneer amplifier.

I have done this many times before with transistor classroom record players, and it worked great. I plugged this thing into my stereo with the classroom record player on, but with no record being played. I heard a moderately loud hum (though not that loud) for a few seconds, and then my amplifier went totally dead. The amp would turn on, light up, but there was absolutely no sound going through. I opened up the amplifier to find that I had blown two 1 amp fuses, and hopefully nothing else. I'm heading out tomorrow to get some fuses. Any ideas?

[Brad]

Hard to say for sure but it is likely that one the units (likely the older one) has a hot ground and when you connected it to your Pioneer you essentially shorted the hot side of AC mains (on the old unit) to ground on the Pioneer. You are lucky would weren't touching metal on both units as you plugged them in.

You will have to isolate the two with either a transformer or capacitors.

(So which model Pioneer do you have? I still have my SX-680 from 1978)

[Shane]

That makes sense to me. I replaced the two fuses today, and amplifier is (very very thankfully) back to normal. I will not be trying to hook up that record player again!

I have an Pioneer SA-500, which dates from around 1973 or so. Picked it up for $15 at a sale where some guy pulled up into an empty roadside lot, unloaded his truck full of junk, and started selling. This thing sounds great, is small in size, and has proven to be very reliable. I'm glad to see it working once again!

http://www.classicaudio.com/value/pio/SA500.html