Changing Impendence on 4 x 12 cab

[Aussie Battler]

Howdy People i have a 1960 TV 4 x 12 cab with 80s reissue greenbacks 25w and its 16 ohms and i have just bought a head that only switches between 4 or 8 ohm .
My question is i have seen aftermarket switches that have selectors between 4/8/16 and are these just plug and play or does the cabinet also need rewiring to accommodate the difference in the range of impendence .
I'm in Australia and i would have to source this from the states and wanted to be sure whether a plug and play exists or theirs no escaping a rewire as my preference would to have the 4/8/16 ability as i have a few different heads .
If anyone could give me some advice on this would greatly appreciated.

 

[AdrianDSL]

You can turn a 4 speakers 16ohm cab into a 4ohm one by rewiring it. If all speakers are 16ohm, they'll all go in parallel. For 8ohm 2 of the speakers will be bypassed, or you can wire it with 2 8ohm inputs using all 4 speakers, 2 per input.

https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/

 

[Aussie Battler]

Thank you so bottom line is i need to add another input or switch to do that and i'm assuming the 8 ohm option would then be stereo and still require rewiring of the cab

 

[fitz]

Thank you so bottom line is i need to add another input or switch to do that and i'm assuming the 8 ohm option would then be stereo and still require rewiring of the cab

No, all four 16 ohm speakers in parallel to one jack is 4 ohm.
Just connect all positive speaker lugs to the jack tip, and all negatives to sleeve.
Unless you want the stereo 8 ohm with a multi jack plate.
There are aftermarket kits that come with the jack plate and wiring harness for about $20(?).
They let you do all the options with a quad of 16 ohm speakers.

 

[Aussie Battler]

Thanks I think I will look into the plug and play option , it looks like it needs rewiring so I'll have a look at how hard that is as I've never had a crack at doing that before

 

[fitz]

Thanks I think I will look into the plug and play option , it looks like it needs rewiring so I'll have a look at how hard that is as I've never had a crack at doing that before

Plug and Play Jack Plate

The Plug and Play Jack Plate is a complete drop-in assembly for stereo speaker cabinets. The standard version shown below is marked for the 8 Ohm Stereo and 4/16 Ohm Mono. This is a common setup with guitar cabinets. What is uncommon is the elimination of the switch. This makes connecting the...

www.mojotone.com

These are also available on ebay and amazon.

 

[RLW59]

That cab should have the round, single jack cup so you'd need to cut the rear panel to mount any of the rectangular switching jack plates.

The speaker wires are probably soldered to the single jack (instead of having the push-on connectors that most switching jackplates are designed for).

Depending on which reissue greenbacks are in it, they might have the old-style solder-only speaker terminals.

Adding a switching jack plate may be a relatively big job. Rewiring the single jack for 4 ohms only would be simple if you can solder.

Can you post some pics? And remove the bckpanel for pics of the connections on the jack and speakers?

 

[Monstercastle]

Will the amp tolerate the typically considered safe mismatch of connecting the 16 Ohm cab to the amps 8 Ohm output?

 

[2L man]

Will the amp tolerate the typically considered safe mismatch of connecting the 16 Ohm cab to the amps 8 Ohm output?

Usually they do if not driving amp too hard. If player does not understand why that setup volume is lower and turns vol to 11 the power tubes and/or Output Transformer might destroy.

I think it is better to use correct output load which has less speakers than wrong load which has more speakers or cabinets.

 

[william vogel]

The problem with mismatched impedance is that you’re changing the output characteristics of the amp. If you are purposely doing it because through testing with a scope and measurements you’ve found a characteristic that is appealing or intriguing to you, then go for it. If you’re attempting to compare different speaker types and brands, the tonal changes from impedance will give a false representation of what the properly matched impedance will sound like. When I play around with loads on amps, it bends the waveform along with changing the voltage output. Sometimes it’s beneficial and sometimes it’s degrading. It’s always best to match the impedance unless you’ve found it to benefit with use of measurement instruments.