Limited Edition Ampeg SVT

[bagsieblue]

My brain hurts!

[Hellzero]

Cabinet "x" Ohms ≥ Amplifier "x" Ohms.

 

Or is still too complicated @bagsieblue ?

[dmccombe7]

2 hours ago, Hellzero said:

And you are right.

 

To keep it simple with (valve) amplifiers always use the amplifier's output (tap) matching the cabinet impedance, never use a lower impedance cabinet than the output impedance (tap) chosen on the amp, but you can use higher impedance cabinet than the impedance of the amplifier's output (tap), even if it can create some slight distorsion or slight out of phase sound, which you won't really notice and certainly not the audience.

 

Clearer?

That's better 

[dmccombe7]

If the sun is in the East then lean to the West.  

Dave

[agedhorse]

6 hours ago, Hellzero said:

And you are right.

 

To keep it simple with (valve) amplifiers always use the amplifier's output (tap) matching the cabinet impedance, never use a lower impedance cabinet than the output impedance (tap) chosen on the amp, but you can use higher impedance cabinet than the impedance of the amplifier's output (tap), even if it can create some slight distorsion or slight out of phase sound, which you won't really notice and certainly not the audience.

 

Clearer?

No, some tube amps are particularly sensitive to a higher impedance load, because the reflected impedance to the tubes an primary of the OT can cause ringing and larger than expected voltage spikes which can damage OT’s, tubes and in some cases arcing between the pins of tubes.

[Hellzero]

18 minutes ago, agedhorse said:

No, some tube amps are particularly sensitive to a higher impedance load, because the reflected impedance to the tubes an primary of the OT can cause ringing and larger than expected voltage spikes which can damage OT’s, tubes and in some cases arcing between the pins of tubes.

Much higher impedance loads, not putting an 8 Ohms cabinet on a 4 Ohms output transformer (OT) tap... 

[BigRedX]

For solid state amps the cabinet impedance must be equal or greater to the minimum impedance marked on the amplifier's speaker output sockets.

 

For valve amps with multiple speaker outputs marked with different impedance values the cabinet MUST be of the same impedance as the output it is connected to.

[dmccombe7]

3 hours ago, BigRedX said:

For solid state amps the cabinet impedance must be equal or greater to the minimum impedance marked on the amplifier's speaker output sockets.

 

For valve amps with multiple speaker outputs marked with different impedance values the cabinet MUST be of the same impedance as the output it is connected to.

Still no wiser. but this makes a lot of sense to me if i want to be on the safe side.

Dave

[agedhorse]

20 hours ago, Hellzero said:

Much higher impedance loads, not putting an 8 Ohms cabinet on a 4 Ohms output transformer (OT) tap... 

Not necessarily, some tube amps are fairly sensitive to output stage loading. A 50% mismatch could result in double the L(dI/dT) voltage which can over time (or immediately) break down insulation in the output stage. 

[Hellzero]

6 hours ago, agedhorse said:

Not necessarily, some tube amps are fairly sensitive to output stage loading. A 50% mismatch could result in double the L(dI/dT) voltage which can over time (or immediately) break down insulation in the output stage. 

You still can rebias the output stage tubes to this specific load to avoid this, but nobody will do it, except some crazy techs. 😉

 

And yes I've seen some melted output transformers in my life, but way more blown speakers leading to this, both for mismatched impedance.

[agedhorse]

2 hours ago, Hellzero said:

You still can rebias the output stage tubes to this specific load to avoid this, but nobody will do it, except some crazy techs. 😉

 

And yes I've seen some melted output transformers in my life, but way more blown speakers leading to this, both for mismatched impedance.

How would you propose to change the impedance matching by re-biasing? Bias does nothing to the high reflected impedance LxdV/dT effect.