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[Tom Phillips]

...they want an amp that sounds like a factory correct 59 Bassman, and I'm like...do you really even know what that sounds like?....

I think that it's just a way of expressing that they want a well maintained amp with period correct circuitry. Maybe not the selenium bias supply rectifier though.

In 1959 the amps were not used to create the sounds that players lust after today. The line voltages were lower, the amps were set to a colder bias point and the power tubes were not matched sets (although the off-the-shelf tubes were closer matches than we would expect today.) Furthermore, it was not common to intentionally overdrive the amp. In the 50's and early 60's the sound of power amp distortion was often confused with blown speakers. Most players believed that they would quickly damage the speakers if you turned up the amp too high and they would freak out if another guitar player did that to their amp.

[Helmholtz]

In 1959 the amps were not used to create the sounds that players lust after today.

Leo might not have had distorted sound in mind.
But early electric blues players soon found out.
Just listen to 50s recordings with Muddy Waters, Hubert Sumlin, Earl Hooker, BB KIng, Buddy Guy, Otis Rush, Johnny Guitar Watson and many others.

[Greg_L]

Well the issue apart from tone still remains. Where 1k can absolutely make a difference. As noted by Helmholtz 6.6k at 400V (I think the TW Express is between 410V and 420V) is already borderline. Increase the Raa from there and it's probable the screens will over dissipate. So there's something wrong then if PAM is marketing an OT with an Raa of 7.5k specifically for an amp that is pretty much intended to be cranked all the time and uses a pair of el34's at 420Vp. Right?

Right no I do get that. Being out of spec for the tubes is a problem. I was just off on a tangent about primary impedance varying but still in a safe range.

[Greg_L]

Turns' ratio doesn't change with age.

Truth, but other stuff does. And so you replace it...and maybe that stuff sounds a little different. And wall voltages increase, and tubes change, etc etc etc and you get to a point where primary impedance being a little off isn't really the sound you're hearing.

[tedmich]

Red China series is cheaper? Do tell...LOL

[Delta362]

I took an amp class held by Bruce Egnater in the fall of last year. He had mentioned Pacific Audio as a viable transformer supplier. That was the first time I had heard of them.

[35L6]

Having more choices of primary impeadence might be a good thing but if the specs are screwy you wonder what they actually ship . I do wonder how much difference you can hear . I suspect you can hear a difference between 8k and 6k6 , but not 6k6 and 6k7 . I've never tested it so don't really know . Has anyone out there tested and is the difference only at full clip ?

[Chuck H]

Having more choices of primary impeadence might be a good thing but if the specs are screwy you wonder what they actually ship . I do wonder how much difference you can hear . I suspect you can hear a difference between 8k and 6k6 , but not 6k6 and 6k7 . I've never tested it so don't really know . Has anyone out there tested and is the difference only at full clip ?

Well if and how much difference with different primary impedances is an easy thing to check/hear for yourself. Not 6.6k compared to 6.7k but consider that many old tube amps had a load "allowance". Like the Fender non compensated "ext" jack. Since we want all other things created equal you'll want to do this with an amp that has an impedance switch. Otherwise changing the speakers will skew the test. So if you have an amp that runs into an eight ohm load you could set the impedance switch for sixteen ohms and you effectively half the primary impedance. How different does it sound?..

Not that damned different in my own experience. When I've had occasion to experiment with this my amp still sounded like my amp. There are some subtle changes but nothing that would have me barking about something being wrong with my tone. And...

The difference clean and during heavy clipping is so small as to be insignificant. When you're clean you'll be hearing mostly the fundamental and the overtones and harmonics that aren't dicordant. When clipping hard there's such a cacophony going on that I'd dare you to pick out something specific. So it's when the amp is set up to just barely clip that you hear the greatest difference between primary impedances. Again, in my own experience.