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    Building, troubleshooting and testing of these amplifiers should only be
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Otl

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fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
SE?

Hi,

So, if you were going to stick to an SE design, with 6080's or something similar, would the output be taken from the cathodes, or the plates?
Click to expand...

For lowest Zo it ist best to take the output from the cathodes.

A circuit that works wel is the SRPP as used by Philips in their EL86/6CW5 amp I remember it driving 8 Ohm speakers with aplomb.

Quite amazing when you consider it ws designed for a 800 Ohm speaker.

Cheers,;)
 
fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
OTL

Hi,

So, Frank, would two 6080's (4 triodes), with cathodes paralleled be sufficient drive for an 8-ohm high efficiency speaker?
Click to expand...

Absolutely!

What you could do is // two triodes and use those as an SRPP for instance.
With a cathode bypass cap that should have low enough Zo to drive your Altecs.

BTW did you know the Altec VOT really love an OTL ?

Cheers,;)
 
fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
FLASH GORDON

Hi,

Just a thought...I'm pretty sure it has never been done but...

If you were to use an input tube you could actually build the outputstage as a White cathode follower.

That would yield the lowest Zo and formidable current possibilities on the output.

Having used a circuit like that with a 12BH7A I can say it would drive any load and it has the best performance of any CF I know of.

You can also consider using an anode choke to further optimize it.
(I haven't tried but on paper at least it seems promising.)

Cheers,;)
 
Joel

Joel

Member
Joined 2002
joeltunnah.com
Like this?

From tubecad journal.
 

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fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
CLOSE TO HEAVEN.

Hi,

That circuit can definitely be used.

Mine is different...not necessarily better.

Using the 12BH7A I have a 1K anode R at 305VDC and a cathode R of 680R.
Between the cathode and anode of the two halves a 680R resistor was used as well.

I didn't decouple the bottom cathode R and the signal was capacitively coupled to the upper grid using a 100 nF cap.

The output was taken at the anode from the bottom tube.

A 1M resistor is run from the anode of the bottom tube to the grid of the upper one.

A well regulated all tube PSU was used as well.

Thsi circuit can be put to service whenever one needs a low output Z and no gain.


Cheers,;)
 
Joel

Joel

Member
Joined 2002
joeltunnah.com
I also read on the "Joelist" that the 6080 is very linear when used as a CF.

Anyway, it seems odd to me how complicated and oversized most OTL designs are. If my example above would work, it would be significantly smaller than say the RCA circuit. Were they trying for large amounts of power into VERY inefficient speakers?:scratch:
I bet also that the large capacitors in the 50's really sucked. You probably couldn't even get a 1000MF cap...
 
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