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CarlyBoy 7th October 2006 03:40 PM

John Broskie's enhanced T8
Anybody build John Broskie's enhanced version of Rosenblit's T8 OTL? Find it here:

What I'd like to do is replace the EL509 with something I have on hand, like 6KV6. I'm hoping someone out there has the technical knowledge and the generosity of their time to explain how I would go about modifying circuit values for a different output tube. Thanks for any input on this.

5u4 7th October 2006 04:47 PM

2 Attachment(s)
Don't have any info on swaping power tubes, or about Tube Cads version other than the obvious question: did he actually build an "enhanced" circuit, or is it on paper only? This was a hot topic on the Transcendent forum a few years back. I built Rosenblit's T8 & it's a fine amp the way it is.

Burnedfingers 7th October 2006 06:56 PM

Could you post the schematic for Rosenblits OTL?

5u4 7th October 2006 08:45 PM

I've seen the schematic on The Internet somewhere, but I'm not about to post it. I think the idea is to buy Rosenblit's book "Audio Reality" available on the Transcendent Sound web site. It has the schematic & test procedure for the T8 as well as other stuff. The only mod I would do is add the chokes (low noise mod) to the power supply.

Burnedfingers 7th October 2006 10:39 PM

I'm sorry that you feel that way. I didn't think I was out of line because it wouldn't be any different that asking for a schematic for a Dynaco Stereo 70 amp.

5u4 8th October 2006 12:01 AM

Please forgive me if I came across as impolite, I didn't mean to be.

Tube Cad used to have Rosenblit's T8 amplifier circuit with all the values, without the power supply, on his web site several years ago, maybe it's still there?

I'm not going to post it because it's a patented circuit & maybe considered intellectual property.

heater 8th October 2006 12:19 AM


I don't understand why you say "I'm not going to post it because it's a patented circuit & maybe considered intellectual property."

Well let's consider intellectual property:

Anything patented is by definition publicaly available, in the patent. The patent would only prevent commercialization of it.

Of course the schematic as published in a book is covered by the same copyright as book, but even then quoting small parts of copyrighted material is generally OK by virtue of "fair use" of the material.

If someone else has published it on the net where is the law that says one cannot point a link to it? That is not copying or publishing in anyway.

Might not be a good idea to use the same name if you want to manufacture someone else design for sale, that may violate a Trade Mark but that is not the case here.

If it was a trade secret, which it is not by virtue of being in the book, it is out of the bag anyway.

Basically "intellectual property" is a meaningless term. It is a broad brush covering patents, copyrights and trade marks and one should consider ones rights under each of those laws.

Me, I'd just post the link.

Burnedfingers 8th October 2006 01:13 AM


I don't know if this will help or not but you could pull up the original Patent #2,773,136 by J. Futterman filed July 30,1953 and issued Dec 4, 1956

References Cited in the file for this patent are as follows:

2,160,788 Riddle May 30, 1939

2,358428 White Sept 19, 1944

2,383,867 Koch Aug 28, 1945

2,428,295 Scantlebury Sept 30, 1947

2,659,775 Coulter Nov 17,1953

Looks like there is an article in the AudioXPress April of 2001

Maybe one could purchase a back copy.

rfbrw 8th October 2006 01:43 AM

Assuming the dibbles don't object

poobah 8th October 2006 01:53 AM

A lot of feathers flying around here.

The reason I don't file patents:

1) I am comfortable with myself... I don't need a big truck. And, I won't get the Nobel Prize anyway...

2) I don't want the rest of the world to know my secrets.

Processes and chemistry is where the real strength lies in patents these days. Topology patents grow weaker by the minute... so should they.

If someone has a schem... just PM it for crying out loud. After all, WHERE did YOU get it?


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