Archon half power plus half the impedance?

[watelessness]

Sooo, yeah. Here I am reading through the Archon manual, which is rare for me, and I stumble onto the passage about when you drop to half power, drop the impedance as well.

What? How did I not notice this before?

I still don't understand it.

Thoughtsm

 

[toothace]

That's what you get for reading...

 

[Boogie]

This must have to do with how they achieve the power drop? I can visualize reasons, but I've never seen this before. Can you scan that manual? It's not available online yet.

 

[elvis]

They disconnect two of the power tubes. That cuts the internal impedance by half, forcing the external impedance to change for proper matching. While it's a mild pain (you have to switch two switches instead of one), it keeps the tone of the 4-tube array since the two remaining tubes can operate in the same mode, they don't switch to triode or rebias or anything. Works really well IMO. It only gets you a slight change in volume, so your call whether you would even use it. I use it that way at home to save the tube life, though at low volume I doubt it has any effect anyway.

 

[watelessness]

Boogie, here is your manual. I found that cutting the impedance really worked. It seemed too loose and out of control when leaving it at 16 ohms, but 8 is perfect as it retained the headroom but brought back some of the control. 4 ohms sounded great but was just too compressed. Shawn checked with Doug and it's fine to play around with the impedance. \m/ \m/

 

[Deleted member 5962]

Thanks! That clarifies it once and for all. 100 watt does disconnect two tubes, 50 watt versions switch pentode to triode.

 

[aristotle]

In a 4xEL34 class A/B push pull output stage, removing two of the output tubes from the circuit doubles the primary side impedance. If the secondary impedance remains unchanged, the windings ratio needs to double if you want to keep the impedance matched, which is what happens when you move the amp's selector to the next lower impedance selection. Alternatively, you could double the load impedance by going to a different cab.

 

[Boogie]

Boogie, here is your manual. I found that cutting the impedance really worked. It seemed too loose and out of control when leaving it at 16 ohms, but 8 is perfect as it retained the headroom but brought back some of the control. 4 ohms sounded great but was just too compressed. Shawn checked with Doug and it's fine to play around with the impedance. \m/ \m/

Thanks bud! I love learning a little more about amp designs. Thanks to Aristotle and company for the explanations.