Why can't I...

[Cliff Schecht]

My 5C3 build has 3 separate jacks for 4, 8 and 16 Ohm speaker taps. Why can't I connect a 16 Ohm speaker to the 16 Ohm tap and an 8 Ohm speaker to the 8 Ohm tap? Or can I.. I've never heard of this being done, probably for good reason, but I'm failing to see the fault in doing this..

[paulster]

Because the net load on the OT will be twice (the current) or half (the resistance) when you look at it from the primary side.

What you can do though is to hook at 16ohm cab to the 8ohm output and an 8ohm cab to the 4ohm output at the same time and it'll be blissfully happy.

[rdjones]

My 5C3 build has 3 separate jacks for 4, 8 and 16 Ohm speaker taps. Why can't I connect a 16 Ohm speaker to the 16 Ohm tap and an 8 Ohm speaker to the 8 Ohm tap? Or can I.. I've never heard of this being done, probably for good reason, but I'm failing to see the fault in doing this..

I think what you should try is the 16 Ohm speaker on the 8 Ohm tap, and the 8 Ohm speaker on the 4 Ohm tap.

I tried it, (it's been a while) and I seem to remember it looking better on the scope than the supposedly correct connections. I also tried an 8 Ohm dummy load on the 8 Ohm tap and an 8 Ohm speaker on the 4 Ohm tap. Nothing blew up ...

rd

[dynaman]

Because the net load on the OT will be twice (the current) or half (the resistance) when you look at it from the primary side.

What you can do though is to hook at 16ohm cab to the 8ohm output and an 8ohm cab to the 4ohm output at the same time and it'll be blissfully happy.

Ahh, I always wondered about that scenario. What if....you plugged an 8 ohm cab into the 8 ohm output and plugged a 16 ohm cab into the 4 ohm output? Same result? There's no reason to, but......

[paulster]

Because the net load on the OT will be twice (the current) or half (the resistance) when you look at it from the primary side.

What you can do though is to hook at 16ohm cab to the 8ohm output and an 8ohm cab to the 4ohm output at the same time and it'll be blissfully happy.

Ahh, I always wondered about that scenario. What if....you plugged an 8 ohm cab into the 8 ohm output and plugged a 16 ohm cab into the 4 ohm output? Same result? There's no reason to, but......

No, not quite. Think of it as resistors in parallel. Each of the 3 transformer outputs can be considered separate windings.

So you have winding A which gives a defined plate load if terminated with a 4ohm load, or an infinite plate load if unterminated.
Windings B and C do the same for 8 and 16ohms.

Then you put the plate loads in parallel to get your true plate load, which usually involves two of the windings being unloaded and therefore having infinite effective resistance and no effect on the parallel calculation.

As soon as you have one of the windings connected to its expected load (your 8ohm connected to 8ohm example) you can't retain the true plate load except by having both of the other windings left open.

In the case of 8ohm connected to 8ohm and 16ohm speaker connected to 4ohm output you'll have a plate load of 80% of usual, so not completely out of whack but still not what's expected.