Head to speaker help

[townandy1]

Ok, I’ve been using Marshall for 30 odd years so I should know this but it still confuses me.
Want to settle the argument of the old ohms argument in a way that my tiny brain understands.

I use a JCM900 head through a 1960A cab.

I always had it plugged in at 8ohms but then someone told me I should have it at 16.

I don’t always use my own cab if the venue has one so sometimes there’s only an 8ohm or sometimes not even a label.

Just want to know if there’s an easy way to show what I should do, so that I can save it on my phone for when I can’t remember

Thanks in advance

Andy

 

[fitz]

I use a JCM900 head through a 1960A cab.

I always had it plugged in at 8ohms but then someone told me I should have it at 16.

I don’t always use my own cab if the venue has one so sometimes there’s only an 8ohm or sometimes not even a label.

Just want to know if there’s an easy way to show what I should do

You should match the amp output to the cab impedance.
Running a mismatch will place added stress on the amp and decrease tube life or potentially damage the OT.

Stock 1960 cabs are usually 16 ohm (or switchable to 16 ohm / 4 ohm / 8 ohm stereo) - if you've changed speakers, it may be different.
If you don't know what the cab impedance is, check the DC resistance with a multi-meter on a speaker cable into the cab.
If you don't have a little inexpensive multi-meter, get one.

 

[Geeze]

When measuring with a DMM you'll get readings less than the actual - i.e. around 6 ohms for an 8 ohm load and around 12 for a 16 ohm load.

Russ

 

[Edgar Frog]

When measuring with a DMM you'll get readings less than the actual - i.e. around 6 ohms for an 8 ohm load and around 12 for a 16 ohm load.

Russ

That's true some of the times. I've had several the read actual ohms rated and some that read little over. My last 4x12 I just donated recently was rated at 8ohm and actual reading with a 3ft 14awg cable read in at 9.5 ohms. So it can be dead on or a little over or under and not always a little under.

 

[Matthews Guitars]

Is the 1960 a stereo (two jack) or mono (one jack) type?

Run cable from 16 ohms to 16 ohms jacks.

Or 4 to 4, which you'll have available on a 1960B.

Pay attention to the switch and jack labels on the cabinet. If it's the stereo type.

 

[BlueX]

Ok, I’ve been using Marshall for 30 odd years so I should know this but it still confuses me.
Want to settle the argument of the old ohms argument in a way that my tiny brain understands.

I use a JCM900 head through a 1960A cab.

I always had it plugged in at 8ohms but then someone told me I should have it at 16.

I don’t always use my own cab if the venue has one so sometimes there’s only an 8ohm or sometimes not even a label.

Just want to know if there’s an easy way to show what I should do, so that I can save it on my phone for when I can’t remember

Thanks in advance

Andy

If you don't know what the cab impedance is, check the DC resistance with a multi-meter on a speaker cable into the cab.
If you don't have a little inexpensive multi-meter, get one.

+1 on getting a DMM, and always measure the resistance of speaker/cab!

This kind of cable can be useful, particularly if you're gigging and there is bad light. It plugs into the cab (1/4" jack) and the DMM (two 4 mm banan plugs).

Amazon.com

 

[Edgar Frog]

+1 on getting a DMM, and always measure the resistance of speaker/cab!

That's a cool little cable. I use a pedal coupler to read cabs as well for a more direct read by eliminating the resistance of the cable all together. I bought several straight and offsets for my pedalboard and decided shortly after they are not good for the pedals and also very inconvenient. They come in handy for other things though. So not a total loss.