Primary impedance OT question

[Muttleyboy]

What effect does the primary impedance have on bass/treble/break-up/headroom?

In the same amp with all other things being sort-of equal, what would be the expected difference in tone using a 4K primary vs 5K3 vs 6K6?

Also, I've read that Matchless Amps used "output transformer mis-matching" in order to achive a certain sound...What would have been the primary impedance of the OT's in a Chieftain or Clubman using EL34's?

Thanks,
Chris.

[tubeswell]

What effect does the primary impedance have on bass/treble/break-up/headroom?.

Hi Chris

The answer is complex. All other things being equal, higher load resistance = more output power up to a point. But headroom (and frequency response) is also affected by the B+ voltage, the screen voltage, the bias point, the tube's transconductance, the source impedance and the load/input impedance of the stage, the inter electrode capacitance of the tube (which is affected by screen voltage) and the amount of iron in the OT. These are all inter-related variables.

[Muttleyboy]

Hi, I didn't from my question very well.

I've read that some output transformers are available with multiple primary taps.

In the same amp with the B+ being more or less the same, and assuming that the tube are biased pretty much the same, how would switching from a 4K tap to a 6.6K tap effect the sound of the amp (In this case a JTM45/Bassman type of amp)

[martin manning]

About the same as switching an 8-ohm speaker from the 8-Ohm secondary tap to the 4-Ohm secondary tap. In other words, there will be some change in tone which depends on the tubes and transformer in use, among other things, and it may or may not sound "better" to your ears.