Speaker ohm testing

[Bruceman]

For the first time tonight I got out the multimeter and tested all my speakers. On my old Silvertone 2 x 12 model I got 7.4 on one and 1.5 on the other. Even tho I think I know the answer, being a fledging electro-maniac I wanted to ask the experts. (or someone that knew) !

What's with the 1.5 reading? And I'm guessing the 7.4 would be called an 8 ohm speaker?


thanks

[Marble]

were they still wired together when you tested them?

[Patrick620]

Originally Posted by Marble

were they still wired together when you tested them?

and disconnected from the amp?

[Bruceman]

Yes, they were still wired to the amp.

[Fader]

Isolate the speakers from any wiring and try it again.
Depending on the wattage, you should get a reading of around 5 ohms if it's an 8 ohm speaker and around 12 ohms for a 16 ohm speaker.

The difference is because you are measuring only the resistance of the coils and not the impedance. Impedance is the combined resistive and reactive components of the speaker load.

[Bruceman]

So.....without th speaker being loaded, is that why an 8 ohm will read approx 5 ?

[SatelliteAmps]

Originally Posted by Fader

Isolate the speakers from any wiring and try it again.
Depending on the wattage, you should get a reading of around 5 ohms if it's an 8 ohm speaker and around 12 ohms for a 16 ohm speaker.

The difference is because you are measuring only the resistance of the coils and not the impedance. Impedance is the combined resistive and reactive components of the speaker load.

It has nothing to do with wattage. A three watt speaker and a hundred watt speaker will both measure roughly 20 percent under when measuring impedance with a resistance checker.

[Bruceman]

Thanks for the info guys. I gotta pull the Silvertone apart a bit to isolate the speaker wiring. Then I'll measure them again. I hope the speakers are ok cause the way the chassis is made the tubes are in the way of installing speakers with larger magnets. These magnets are really small. Still trying to date the amp. No doubt it's a 50's something cause all of the large 1960 Silvertones I see are grey two piece units. This one is 2 tone brown and the speaker face is slightly angled.

[SatelliteAmps]

Get some EIA codes off either the speakers, transformers, or potentiometers, and you can find the date really quickly.

[Bruceman]

ok - will do.
thanks.

[Bruceman]

Here goes:
pots = bb2917 / 137707 1 meg

speakers = V12L7 / 328547

Trans - Freed 24246

Speaker wires go into chassis and are hard wired to a coil or little transformers...remember, I'm a fledging electro-rookie - the number on those things are 328609

Appreciate the help!

Bruce

[Bruceman]

bump

[SatelliteAmps]

Pot code indicates CTS (137) 1957 (7) week 7 (07). Can't be earlier than that. Usually parts were made a few weeks or months before a product was released. That's a pretty safe bet, about mid 1957. The 7 indicating year could indicate 1947 or 1967, but that amp wasn't made in that covering in either of those years.

[Bruceman]

Cool. Thanks! It has four 6L6's and a fairly big tranny. I can hardly wait to fire ''er up. Hope I can find some speakers with small diameter magnets to fit. I just imagine it will sound better with better speakers than 1957 Silvertones. Any info on those speakers numbers? Thanks for your help. Really appreciate it.

[SatelliteAmps]

328 is the code for Utah. Same code system for year and month. Those speakers are actually pretty good sounding in that amp, if they are the stock ones. If it's the amp I think, it is actually a stereo amp, running two power sections through two output transformers, one into each speaker. Great tremolo when it is working correctly.