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Old 18th September 2010, 10:36 PM   #1
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Default Long-tail pair phase splitter

Is this generic schematic of a long-tail pair phase splitter correct? Are there any additional parts (resistors or caps) that need to be added? I am using the schematic in a review. I drew it from looking at numerous variations on several websites.

John Johnson
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Old 18th September 2010, 10:55 PM   #2
DougL is offline DougL  United States
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You are missing the plate load resistors, and perhaps output capacitors. You are also missing grid stoppers, and the input cap may be optional, depending on the presiding stage. And I almost forgot, where is B+? (called Vcc by the vulgar)
By the way, that is not a long tail pair. A Long tail pare would have a negative supply. Idea is that the cathode resistor is very large, to approximate a CSS.

HTH

Doug
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Last edited by DougL; 18th September 2010 at 11:00 PM.
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Old 18th September 2010, 11:24 PM   #3
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This is where I got most of the schematic for a long-tail pair phase splitter:

The Long-Tail Pair

Is his schematic incorrect, or did I just leave something out of my own schematic?
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Old 18th September 2010, 11:27 PM   #4
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Quote:
Originally Posted by sdinfo View Post
This is where I got most of the schematic for a long-tail pair phase splitter:

The Long-Tail Pair

Is his schematic incorrect, or did I just leave something out of my own schematic?
Requirements to values of long tail resistors and cathode bias resistors are very different. If you use in your schematic the value that is good for LTP tubes will be starving. If you use the value needed for proper bias it's no longer a LTP since the value of this resistor is too low for LTP.
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Old 18th September 2010, 11:28 PM   #5
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check out merlin's pages. Very easy to understand, and practical
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Old 18th September 2010, 11:32 PM   #6
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Perhaps this one would be better to draw from (the schematic at the bottom of this URL):

http://www.angelfire.com/electronic/...Amp-Phase.html
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Old 19th September 2010, 03:01 AM   #7
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nope - same issue identifed above by waveborn - thats a short-tailed pair...

The better one is this one

Click the image to open in full size.
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Old 19th September 2010, 03:09 AM   #8
Brit01 is offline Brit01  United Kingdom
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If you want a LTP with very closely balanced signals then probably a small pentode as the current sink is best.
I am just about to try this but with a SV83. EF86 is described below.


Quote:
The ra of the pentode is so high compared to its cathode resistor that r(ccs) can be approximated as being equal to ra. In this case it is roughly 2Meg, so this circuit has the effect of using a 2Meg tail resistor on the long tailed pair, without the drawbacks! The performance of the long tailed pair becomes so perfect that its anode resistors can be made equal and excellent balance is ensured (see the sections on the long tailed pair for the rest of the circuit).
Swap the 47K resistor for the pentode current sink.
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Old 19th September 2010, 03:13 AM   #9
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or, for ultimate ease - a sand CCS. 317 anyone?
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Old 19th September 2010, 05:57 PM   #10
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Thanks much. I will probably use the layout that aardvarkash10 illustrated.
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