patent on single-ended amplifier, anno 2008

[ErikdeBest]

Today I was looking at scholar.google.com and typed in 'valve amplifiers', to see how many citations Morgan Jones collected with his fantastic book. I was a bit surprised to find a patent for a single ended amplifier, filed ii 2006 (published in 2008).

http://www.google.nl/patents?hl=nl&l...age&q=&f=false

Application number: 11/490,453
Publication number: US 2008/0018397 A1
Filing date: 21 Jul 2006

Although patents should always be novel, I know it is not always the case. Still I can't instantly identify the circuit... looks like a cascode under an active load (sort of mu-stage) for the driver, but not really... the output is a pentode, with (poorly) regulated screen.

I will read the whole patent in the weekend, which I hope will be very nice for everyone here!

[disco]

An output transformer at the cathode seems noval. Wonder what the optimal turns ratio will be.

[Arnulf]

It looks like a regular mu-follower, composed of two cascodes (with pentodish characteristics), in other words an extremely high gain amplifier, driving a cathode follower.

What's next, a patent on perforated toilet paper rools ?

[ErikdeBest]

Originally Posted by disco

An output transformer at the cathode seems noval. Wonder what the optimal turns ratio will be.

Not very novel, just not that common as the driver stage needs much more gain compared to a driver stage used for 'standard circuits'. Morgan Jones, Broskie, Tubelab.com and other go into detail about this circuit!

It looks like a regular mu-follower, composed of two cascodes (with pentodish characteristics), in other words an extremely high gain amplifier, driving a cathode follower.

Yes, cascoded stages was my first thought as well, but I only know cascodes with a fixed DC on the upper valve (AC is shunted to ground through a capacitor...).

In this patent the grids of the upper valve just swing with the signal (although I don't know how much, as the schematic doesn't indicate values for the resistors R6, R7, R8 and R9). But there is, indeed, a mu-stage there...

[SY]

Frankland also patented the use of a cathode follower to drive an output stage into AB2. This says a lot about the quality of the patent examination process.

[djn04]

This is just the application the issued patent is 7,511,571

[richwalters]

Eric, Initially can't see what is new or novel about the claims. We all know cathode follower power stages require demanding drive voltage swings and this fact is mentioned in MJ on p.390; Valve amps 3rd edit and this book has copyrights to the wording used well before the date of the patent and I thought would refute the relevant claims. It could well be that the person has uncovered a loophole, reseached the market that there isn't an SE cathode follower design around and decided to pounce.

Gloves off time. Claim 0019:

Technicality: The screen isn't hardwire connected to the plate, correct but for the sake of the DC electron flow it is, but at a lower potential. On AC signal grounds (as I see it) the circuit behaves as a triode cathode follower because the screen is not AC modulated by the anode nor cathode but merely contributing to the fixed low impedance DC electron flow that is not influencing the signal. So I dispute the terminology; (I think the claim is poorly defined)
Claim 0018; The screen regulation; Anything new out of the Radiotron Hnbk ? This section could do with a thick black line throught it. For nearly a century, everyone in the industry knows the screen feed is fussy business. Old dust.

I've got a feeling this thread is going to be a drawn out one.

richy

The claims are as thin as air.

[Yvesm]

IMHO, forcing the CF screen to follow its cathode should have been a better idea

But this seems to be in contradiction with claims ! Who knows ?

Easy to do just by feeding the anode of Z2 and C6 from the primary of the OPT.

Must I patent that ?

Yves.

[SY]

I thought would refute the relevant claims. It could well be that the person has uncovered a loophole

Or most likely, the examiner never bothered looking. I'll give that a 99.9% probability. Unlike the European system, US patent applications are not open to public comment before issuance. The examiners will typically run a quick patent search and that's pretty much it- no literature searching or (in my experience) even a Google.

[Arnulf]

Originally Posted by ErikdeBest

In this patent the grids of the upper valve just swing with the signal (although I don't know how much, as the schematic doesn't indicate values for the resistors R6, R7, R8 and R9). But there is, indeed, a mu-stage there...

I believe this arrangement provides for somewhat lower gain (internal NFB) and possibly injects some power supply noise (so it gets reduced at the output), nothing novel here.