Teac BX-500 question

[mildewmatt]

Hey guys.

Long time reader, first time poster.

In what is my first genuine foray into older solid state gear, I have recently acquired a Teac BX-500 and it's matching TX-500 tuner. Call me shallow, but I fell in love with the VU meters.

I have a question regarding OHMs. I know, I know. Can receiver rated to xohms drive speakers rated to yohms. You hear it all the time.

I have a set of Subsonic XM-3s rated to 6ohm. The service manual for the Teac stipulates minimum 4ohm (likewise other online sources suggest 4-16ohm loads for a or b speakers driven) however the back of the amplifier states a minimum of 8ohm.

I'm aware that using a lower ohm load speaker increases current and demand on the amplifier, and can damage both if not matched appropriately.

I'm rather fond of my recent acquisition and of my entertainment unit hence would prefer neither to be on fire. My questions are as follows:

1. Should I take the advice of the rather authoritative looking service manual, or err on the side of caution and follow the labelling on the back of the amplifier?
2. The speakers are currently bi-wired (not bi-amped) and I have lost the bridge because I'm a nong. I've done some reading, but haven't managed to convince myself. Will this have an effect on the ohms at the amplifier? (also, a+b driven stipulates 16-32ohms on the amp!)
3. I like my speakers a lot, and honestly quite like my regular duty amplifier (a NAD 356bee) - would I be better off not taking the risk and just buying a small set of bookshelf speakers and make it a bedroom system?
4. The back of the amplifier rates input power at 100w, as does the service manual. Output power is quoted at 55w/channel. Assuming the amplifier is 100% efficient (I know it's not), does the extra 10w come from the electricity fairy? How does that even work?
5. Given the relatively low power drawn, is that even more evidence to suggest I should avoid low ohm speakers?

Sincerely,
Anxious. (Matt)

 

[DeltaWye]

4. The back of the amplifier rates input power at 100w, as does the service manual. Output power is quoted at 55w/channel. Assuming the amplifier is 100% efficient (I know it's not), does the extra 10w come from the electricity fairy? How does that even work?
5. Given the relatively low power drawn, is that even more evidence to suggest I should avoid low ohm speakers?

I downloaded a copy of the service manual and I see it uses a 1A fuse for 220V/240V markets and a 2A fuse for North America. Also, see this picture:

http://www.elkristin.de/pics0412/7_N19032013_f_036.jpg

So assuming you're in North America, it should draw somewhere in the area of 200 watts at 120. Perhaps your unit was from Europe and was converted to run off of 120V.

Regarding speaker impedance, I'm surprised that a unit like this from the late 70s would not be rated for 4 ohm speakers. As you said, the service manual says it's okay. Maybe yours is a newer unit and they starting putting in modules only rated for an 8 ohm load instead of discrete transistors, I have no idea but there's a good chance someone here will know about these Teacs.