180W Studio Bass

[Smokebreak]

Thats a good idea!
I haven't measured output. What's your favorite way to do it?

[pdf64]

Scope and measure the Vac of the output across a suitable load resistor and feed a ~200mV ~400Hz signal in.
Set any tone controls for best flat response and increase volume until the output wave just starts to hit the rails.
The RMS equivilant Vac, squared and divided by the load resistance = power output.

[Smokebreak]

Cool. I'll plug in my scope one of these days and see whats up. I've got an old heathkit that someone gave me .

[teemuk]

Interesting with the PI then the CF driver before (6) 6l6GCs and no bias pot but what looks like a possibly useless "output balance" or "output tube matching " on another schematic.

I would guess that when they designed this stuff variation between tubes wasn't as great as it is now. And if output tubes were assumed to bias reasonably close to their designed operating point it didn't make much sense to introduce a control for that. (e.g. Even today many Mesa/Boogie amps omit the bias control because it is an unneccesary feature when you use Mesa's tubes).

On the other hand, balancing the quiescent current of the push-pull sides will reduce distortion, particularly even order, since the push-pull circuit will work more symmetrically and due to that reduces the even order distortion it makes. Balanced operation will also reduce DC over OT so the transformer will work more efficiently and perhaps musters few extra watts.

Those days all that made perfect sense as Fender was trying to make louder and cleaner amps.

Oh, one particular feature of high-value tail resistor is that it also enhances balanced operation of the phase inverter, and thus the entire push-pull circuit. As first stage that "phase splits" it's probably the most important stage to balance too. So, those component values simply reflect design choices that reduce distortion and enhance symmetric operation of the push-pull circuit. They didn't even try to make another Bassman.

Those amps are heavy as is , but they are begging for a choke !!

I remember someone researching that topic and finding out that the "ultralinear" circuitry in these Fender amps isn't really that. The tapping point is simply incorrect to achieve "ultra linearity" in great degree. What looks like ultralinear circuit is actually closer to cheap method of deriving a choke from windings of the output transformer.