Need an audio brainiac...Stumped...

I replaced the xover caps and whats wierd is that 4 other amps work great with the Altecs and the dynaclone works great with any other speakers save those Altecs.. Got a set of Valencias in storage id like to pull and see how they behave since the voice coil/mag structure is the same betwenn the Santanas and Valencias. Mybe it is some inductive quality that only is present in Altec drivers..Thanks for the thought - best regards

Hey Guys, Its solved. Most of us were on the right track with the various inductive properties mismatch theory and it turns out, after studying crossover theory that the cure seems to be a "Zobel" series RC network in paralell with the amps output. Many crossover designs actually incorporate these in the LF driver portion of the crossover to make the amp "feel" a constant impeadance and thusly make it a happy camper with "bangy" high inductance, super reactive unstable feeling alnicos.

I started with a 14uf + 10ohm resistor which stopped the motorboating but seemed to take away some of the "umph". I reduced to 8uf + 6 ohms and it sounds smashing. Installed a switch and those components in my amp so I can add or delete the Zobel depending on my speaker choice with a flick of the switch. Looking forward to trying out on some of the other speakers that were non-problemaic to see how fidelity does in comparison with in or out of the Zobel.

Interesting to note; only the big alnico altecs seem to have the massive ammount of inductive kickback to cause the issue. Thanks to all of you for the input and and thanks to Otto Zobel up there in the big laboratory in the sky!

Found a weak HV filter cap (old salvage part) have new one on order. Will be intetresting to see if the Zobel is still needed to prevent the motorboat on the Altecs...