16 Ohm Speakers OK with Magnavox 175?

[SanJoseMichael]

Recently came across some very large home made cabinets that contain Altec 803b bass drivers (16 ohms per Altec literature) and 804a high frequency drivers (also 16 ohms per Altec literature) with 811B sectional horns. "Dividing network" is an Altec N-800E. Both speakers rated at 30 watts.

Taking resistance measurements, I get about 8.5 or 9 ohms on one cabinet, about 10 or so ohms on the other cabinet.

I believe the output transformers on the Magnavox 175 was about 6 ohms? Is it safe to connect the Altecs to the Magnavox 175?

Thanks!

 

[century tek]

At least according to most of my Magnavox radio and stereo amp schematics, most were noted on the schematic as being 4.3Ω.

16Ω speakers will work fine and won't do any damage to the amp but might be a little quieter than a 4 or 8 ohm speaker so you might have to raise the volume let's say from 2 to 3 to get the same level you would from a 4 or 8 ohm speaker.

 

[SanJoseMichael]

Thanks! My listening levels are not high. I'll give it a try this weekend.

 

[gadget73]

Less power and considerably increased distortion will result. Whether you can tell by ear, I can't say but it will definitely show poorly if you measure that amp into a 16 ohm load vs the 4 ohm that it normally would have seen. Its not likely to hurt anything though.

 

[SanJoseMichael]

We'll give it a try, but not expect to much. I hope to ultimately get to restoring a Scott 299, which does have 16 ohm taps, for use with these speakers.

 

[century tek]

If your speakers are fairly efficient, they should sound fine.

 

[GordonW]

The only issue, is possibly overloading the screens of the output tubes, if you were to get near clipping. With less load on the plates (due to the high impedance speakers), the current from the output tube cathode starts to "sink" in the screens, instead of being pulled to the plates and output transformer. This increases heating of the screens.

Of course, 6V6s don't seem to have much problems with the screens... so it's probably going to be OK...

Regards,
Gordon.

 

[SanJoseMichael]

The Altecs sound quite good with the Magnavox 175! I'm real pleased with this, and now I need to go find some favorite tracks to play...