multi tap windings

[woodyc]

FYI, I just noticed another brilliant Mesa innovation is now in the public domain.



Hey, I also just noticed I'm a senior member now. Yay!

[Tage]

So doesn't this result in lower heater voltages as well? seems like an alright idea otherwise, not really revolutionary, but nothing from Mesa seems to be... or at least it is rarely useful.

[Austin]

So its a switch to reduce the voltage, only on the primary of the power transformer instead of the secondary? The THD Univalve has a switch like that on the secondary so it doesn't reduce the heater too.

[woodyc]

So its a switch to reduce the voltage, only on the primary of the power transformer instead of the secondary? The THD Univalve has a switch like that on the secondary.

Sorry, I should have put a smiley. Where I said "brilliant," I meant "retarded." The univalve way is better.

[printer2]

They got a patent for that? Tapped primaries have been around forever.

[Tom Phillips]

They got a patent for that? Tapped primaries have been around forever.

The US patent office has been lame for a long time. However, the patent may be based on twisted wording in the claims such as "Method to reduce voltage within an electronic device used on stage in smoky bars where inebriated women may flash their..."

[loudthud]

Musicman was using that circuit in the 70's.

[woodyc]

Musicman was using that circuit in the 70's.

Yeah, I guess you'd call that prior art. I think Musicman did it on the primary side in some amps and on the secondary in others.

[imaradiostar]

Patents usually have a disclaimer that you can't patent something that would be obvious to someone knowledgeable in the art. Pretty much any Mesa patent seems like that to me. How do any of them ever get through?

Jamie

[Tom Phillips]

Patents usually have a disclaimer that you can't patent something that would be obvious to someone knowledgeable in the art. Pretty much any Mesa patent seems like that to me. How do any of them ever get through?

I figure that the patent office must make money on each patent that they grant.

[trobbins]

If you're the first to apply a technique to an application (a practical adaptation of a generic principle) then that does hold water for patent acceptance.

Did the Musicman amps specifically identify the line-voltage switch/setting as useful for voltage scaling the operation of the amp down from normal to a 'starved' kind of level, or were they only really designed to allow an amp to cover different line-voltage 'regions', as was the case with most amps from earlier eras.

[Tage]

I like to use some transformers that have two different secondary B+ windings to switch between headroom levels, with cathode biased amps. But switching the primary seems like asking for trouble with low heater voltages.

[trobbins]

As I understand it, although heater voltage below -10% is a reliability concern over a tubes life it wouldn't be too significant as a not too often used mode of operation. Also most cathodes still have lots of emission margin to cope with lower heater voltage levels.

[g1]

Did the Musicman amps specifically identify the line-voltage switch/setting as useful for voltage scaling the operation of the amp down from normal to a 'starved' kind of level, or were they only really designed to allow an amp to cover different line-voltage 'regions', as was the case with most amps from earlier eras.

Not sure about this as I've only seen the Musicman type with switched secondary taps, which is their Hi/Low power switch.

The Boogie switched primary version is labelled bold/spongy in the dual rectifier amps, so it's definitely for sound considerations and not line voltage issues.

[trobbins]

I quick google around and a look at photos indicate MM's early amps tapped the primary of the power transformer at about 60% - which was the 'HI' setting on the front panel power switch - this gave standard heater levels and full power output. With the power switch at 'LO', all secondary levels were pro-rata down. Later models just reduced HT levels, not heater level, and also included standby. I haven't seen a manual, but perhaps hi/lo didn't identify that the amp could actually be used for an application where the musician wanted bold/spongy ;-)