How do boutique makers sell Marshall Circuits?

[jrewing]

HI Guys,
Hope everyone is well. Just a quick question here. Obviously, many boutique amp builders make and sell amps that are based on Marshall and Fender circuits. Are there copyright or legal implications for this? Just curious.

Thanks,
JR

[Haze13]

As I understand, you can not make a patent of a basic gain stage with a particular values. Every thing in marshall/fender amp is done by the book with adjusted values.

[d95err]

Circuits have no copyright. However, a PCB layout of a circuit is usually copyrighted, so you can't copy that directly. Simple point-to-point layouts are probably not subject to copyright, so no problem copying old vintage amps.

[chrisom]

Fender used some RCA tube circuits that were available at the time early on, and Marshall copied Fender's tweed Twin and tweed Bassman circuits themselves, while varying the transformers, filtering, output tubes, then rectification, negative feedback settings and other 'refinements' later as time went on...

[Haze13]

Circuits do have copy rights... Sallen&Key, Baxandal, Darlington, Tube PI - they all have patents, and there are far more patented circuits that we use for free!

[Haze13]

By the way! Sorry for the off-top, but does some one know why back in the day they used tube rectifiers? Neg voltage was done with the help of diode, so that means there were diodes back in the day. What was the logic of using the valve if diodes are more cheap and efficient? Aren't they were strong enough?

[CalGTR]

Circuits are indeed patentable, but any patents on these vintage Marshall or Fender circuits would have long since expired. So, no problem flat-out copying these circuits for commercial purposes.

[d95err]

Circuits do have copy rights... Sallen&Key, Baxandal, Darlington, Tube PI - they all have patents, and there are far more patented circuits that we use for free!

Copyright and patents are two very different things. A circuit patent is for a specific technical solution. It's the general principle that is patented, so for instance, you cannot patent specific component values. A circuit copyright would be for the entire circuit and is not possible. Copying a circuit that has a patented solution would be patent infringement and you would risk being sued by the patent owner.

[d95err]

By the way! Sorry for the off-top, but does some one know why back in the day they used tube rectifiers? Neg voltage was done with the help of diode, so that means there were diodes back in the day. What was the logic of using the valve if diodes are more cheap and efficient? Aren't they were strong enough?

Selenium rectifier diodes were used in old fixed bias amps. They were relative expensive and (I'm guessing) could not handle high voltages or high currents, so they could not be used for the anode voltage of an amp.

[Haze13]

Thanks!