Chasis ground question

[tubedude]

It's also mechanically grounded to the chassis at the input jacks just like the pots. The Earth ground at the plug appears to be decently bolted to the chassis from the pic but hard to tell from that pic.

Theres a good FB group for Tube amp repair, 1065280143547025, a lot of knowledgable people.

And Ampgarage.com

 

[turcmic]

OT but thanks to TB’s amp gurus for these posts on the history of tube amps! Very interesting!

 

[iiipopes]

All the amp builders of the time didn't really drift very far from a standard push pull output, in itself standard enough that any good tech could service them without a schematic. Small changes in parts values were made to optimize (hopefully) for the power supply voltages, the chosen output transformer and the intended purpose, but overall there was nothing innovative, except perhaps when ultralinear came along.

Philips KT series output tubes were a superior tube in many respects, being able to withstand higher plate voltages and drive lower impedance loads in some cases, allowing for higher output power. This, and the fact they were manufactured in Marshall's backyard, and they were likely more cost effective to purchase locally, would have been good reason for Marshall to select them for his product offerings.

No, but it was far enough to make the circuits "proprietary." You need to take a course in what it takes to make something protectible intellectual property, because although all the circuits are similar from a general electronics view, the devil is in the details as to whose circuit is whose due to what modifications have been made by whom in the first instance.

You talk about electronics history: remember there was a time when even the multi-tap secondary side of a mains transformer was new, and all the manufacturers that all used similar "superheterodyne" circuits on their radios. And as you mentioned push-pull amplifier circuits, many of them actually date from the original Westinghouse type 42 amplifier from 1928. But from an intellectual property perspective, these small differences that each manufacturer can claim as its own mean more than the general similarities, when it comes to protectible intellectual property rights, which is the whole point of my first post on this issue.

The same thing has happened with solid state amplifiers. Negative feedback loops to minimize distortion and negative channel feed to increase perceived stereo separation have been around almost as long as commercial stereo records of the 1950's. But it is the finer details in negative feedback and channel separation details that Carver incorporated into his "sonic holograph" circuit, on which he obtained a patent, allowed him to successfully sue Yamaha to stop making certain stereo amplifiers as being too close in their circuitry to Carver's. Again, the history of stereo goes back to the 1920's, and again, the devil is in the details to get something that is protectible from an intellectual property position.

 

[seamonkey]

Early amps had the AT&T and WE patent license sticker on them. When those patents expired, the stickers disappeared.

 

[agedhorse]

IP protection is very tricky and requires a uniqueness that's not an obvious adjustment or modification of prior art that is no longer (or never was as in the case of application notes) protected. For example, you can't claim uniqueness of a circuit because of the values of the resistors used, or because the feedback loop is different (unless the difference is not obvious and not based on prior art, and changes the topology of the circuit and what it does).

There was very little that was protectable in those original circuits, they were commonly used, freely available and related directly to the most basic of circuit topologies.

Circuits that may have been patentable or protected might have included the "Fender Tone Stack", or the Baxandall EQ, but IIRC neither were protected.

As an example of a protected circuit approach is the switchable cascade gain stages for overdrive purposes, here's an example: https://www.guitarplayer.com/miscellaneous/randall-smith-and-the-birth-of-channel-switching

I have a patent that applies to the thermal and overload management of class D amplifiers, it was a very specific approach that took a LOT of R&D and testing to make as simple as it ended up being, resulting in it being quite tempting to copy. It was the non-obvious (until it was dome) approach that made it valuable and also easy to copy.