SE-OTL

Ray P · Post by **Ray P** » Sun Mar 07, 2010 5:18 pm

Nick, hopefully, when I get it built I'll get a feel for the relative arguments.....

The topography isn't like your diagram.

Ray

andrew Ivimey · Post by **andrew Ivimey** » Sun Mar 07, 2010 5:35 pm

I've got Bruce R's book somewhere. Maybe it only has the big brother version; I must have a look for it.

Ray P · Post by **Ray P** » Sun Mar 07, 2010 5:41 pm

OK, from memory, the output stage consists of four paralleld triodes. The cap coupled signal from the driver stage is fed to each grid, along with a -12V voltage. HT is applied to the Anodes and the cathode outputs are commoned (summed) to give the amplifier output. Obviously there are some resisitors in the grid feeds and on the cathode outputs but thats about all the output stage consists of.

Ray

Ray P · Post by **Ray P** » Sun Mar 07, 2010 5:42 pm

andrew Ivimey wrote:I've got Bruce R's book somewhere. Maybe it only has the big brother version; I must have a look for it.

I've got a couple of Bruce's books (Audio Reality and the old intro to tube amps) and the SE-OTL doesn't feature in either of them.

Ray

Post by **Nick** » Sun Mar 07, 2010 6:33 pm

Ray P wrote:OK, from memory, the output stage consists of four paralleld triodes. The cap coupled signal from the driver stage is fed to each grid, along with a -12V voltage. HT is applied to the Anodes and the cathode outputs are commoned (summed) to give the amplifier output. Obviously there are some resisitors in the grid feeds and on the cathode outputs but thats about all the output stage consists of.

Ray

Ok, whats in the cathodes load, is it a resistor or another valve, don't think we are in danger of giving any secrets away, without the drive stage and values its just theory.

If its just a resistor load, then it sounds like a simple cathode follower, I wouldn't have thought that would have a low enough output resistance.

Ray P · Post by **Ray P** » Sun Mar 07, 2010 6:45 pm

Nick, each cathode is connected via a resistor to the 'output bus'.

Ray

Edit: I thought that rather than work from memory it would be better to go upstairs and get the manual and I missed a key component. The 'output bus' has a choke between it and ground. Sorry, but obvously senility is beginning to take hold!

Post by **Nick** » Sun Mar 07, 2010 7:19 pm

Ok, makes sense, so its a choke loaded cathode follower. I guess there is a bunch of feedback wrapped around it to get the 1R output impedance that the web site mentions, 4 6S19pi CF's works out as 33R from what I can find on the valve.

Andrew · Post by **Andrew** » Sun Mar 07, 2010 7:52 pm

"Gain is set at 9 dB. This is perfect for high efficiency speakers when driven from an active preamp or high level source."

"The driver stage uses the magnificent 6H30pi tube."

Must be feedback as it only has 9db gain overall. Mu of 6N30 is ~15 which is ~23db and there's two 6N30P on the pic, so 4 triodes, could be quite a simple driver consisting of a single triode for voltage and a CF to drive the 4 6C19P grids or something more complex, perhaps?

-- Andrew

Andrew · Post by **Andrew** » Sun Mar 07, 2010 7:59 pm

I must admit, it would sort of be tempting to try this type of topology out, its just not something I have heard, but I have way too many other things on the go. Bruce's T16 OTL was quite good at EF 2 , or was it 3?

I hope you can get to a meet Ray I'd look forward to hearing these on the right speakers.

-- Andrew

Will · Post by **Will** » Sun Mar 07, 2010 8:03 pm

The Patent

Cressy Snr · Post by **Cressy Snr** » Sun Mar 07, 2010 8:09 pm

I'd love to have another go at the Transcendent T8.

After all this time I managed to work out what I had done wrong.
Let's just say, it was the bias network turning one half of the output stage full on, whilst the other half was in cutoff.

Now I know why all four valves on the left side of the chassis went into runaway, whilst the other side was unharmed. You live and learn.

Steve

Andrew · Post by **Andrew** » Sun Mar 07, 2010 8:10 pm

Ah, Will, but isn't that his Push Pull circuit

-- Andrew

Mike H · Post by **Mike H** » Sun Mar 07, 2010 9:59 pm

Nick wrote:Ok, makes sense, so its a choke loaded cathode follower.

S - P - L - A - S - H - !

It's as I suspected Watson.

Well not the choke bit anyway ...

Ray P · Post by **Ray P** » Sun Mar 07, 2010 10:33 pm

If anyone is interested, Bruce Rozenblit's book 'Audio Reality', available as a chargeable pdf download from the Transcendent website, includes, amongst other things, information and schematics for the following projects.

The Transcendent OTL
Grouded Grid Preamp
Super Compact 150 Watt Amplifier
Single-Ended with Slam
Grounded Grid Cascode Phono Preamp

He also sells schematics and supporting information for a Single-Ended, Class A, Cathode Follower Amp on his website.

I just mention them given the interest in this thread and have no connection or intention to advocate any of these designs.

Ray

Ray P · Post by **Ray P** » Sun Mar 07, 2010 10:42 pm

Yes, the amp has feedback.

Given the interest I will try to make the Oweston meeting and bring it along.

Ray

audio-talk

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