Marshall 1960 cab Ohms reading high

[Rottweiler]

My 16ohm readings look good at 13.4, but when I measure the 4ohm jack, I get 6.8 ohms. My other 1960 measures 3.5 on the 4 ohm jack as a reference. I only use the 16 ohm jacks.

I've replaced this suspect cab's jack plate a few years back as the 1960 jack plates go bad once in a while. It is possible the replacement jack plate is bad also on the 4 ohm side. I don't remember measuring the 4 ohm reading after replacing it about 10 years ago.

Summary: I just swapped out 2 speakers that were good when I took them out 3 years ago and now I get a high reading on the 4 ohm jack but the 16 is OK. I verified all connectors were snug before closing up.

Any thoughts? Has someone else seen this and have insight? I'm likely to take it all apart and check individual speaker readings and recheck connections.

Thanks,

 

[Deleted member 77333]

All my single jack 16 ohm cabs measure 13 something ohms.
13.5-ish to 16 = 3 ohms
4 to 6.8-ish ohms = 3 ohms roughly.
Its DC resistance so you should be okay.
The rule is you can go higher than spec but never lower.
I would just run those at 16.

 

[Rottweiler]

All my single jack 16 ohm cabs measure 13 something ohms.
13.5-ish to 16 = 3 ohms
4 to 6.8-ish ohms = 3 ohms roughly.
Its DC resistance so you should be okay.
The rule is you can go higher than spec but never lower.
I would just run those at 16.

Thanks for your input. I run my cabs at 16 but I just thought I would ask as there might be something obvious that I was missing. I don't feel like tearing it back apart until I get the bug to switch speakers again!

 

[harddriver]

My 16ohm readings look good at 13.4, but when I measure the 4ohm jack, I get 6.8 ohms. My other 1960 measures 3.5 on the 4 ohm jack as a reference. I only use the 16 ohm jacks.

I've replaced this suspect cab's jack plate a few years back as the 1960 jack plates go bad once in a while. It is possible the replacement jack plate is bad also on the 4 ohm side. I don't remember measuring the 4 ohm reading after replacing it about 10 years ago.

Summary: I just swapped out 2 speakers that were good when I took them out 3 years ago and now I get a high reading on the 4 ohm jack but the 16 is OK. I verified all connectors were snug before closing up.

Any thoughts? Has someone else seen this and have insight? I'm likely to take it all apart and check individual speaker readings and recheck connections.

Thanks,

If this cabinet has the standard Marshall Stereo/Mono switch they are known to go bad for whatever reason. I bought a used cab once where in the 16 ohm setting I was getting like above 30 ohms resistance. I knew the switch was most likely bad so when I got it home I wired it just mono bypassed the switch/and PCB board and the cab read 13.5 ohms like it should have.

Unless you use the stereo mode alot you might want to wired it straight mono with a single jack or put a a more robust switching system in and take that Marshall PCB one out.

It's also not uncommon to get spurious ohm readings at times, but I would usually expect to see 6,8 ohms on an 8 ohm setting.

 

[BeZo]

If this cabinet has the standard Marshall Stereo/Mono switch they are known to go bad for whatever reason. I bought a used cab once where in the 16 ohm setting I was getting like above 30 ohms resistance. I knew the switch was most likely bad so when I got it home I wired it just mono bypassed the switch/and PCB board and the cab read 13.5 ohms like it should have.

Unless you use the stereo mode alot you might want to wired it straight mono with a single jack or put a a more robust switching system in and take that Marshall PCB one out.

It's also not uncommon to get spurious ohm readings at times, but I would usually expect to see 6,8 ohms on an 8 ohm setting.

Yep. Replacing those is preventative maintenance that keeps your amps safe.