LongTailedPair gain -> how to calculate? - diyAudio
 LongTailedPair gain -> how to calculate?
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 20th October 2005, 10:59 PM #1 diyAudio Member   Join Date: Apr 2004 Location: Hungary LongTailedPair gain -> how to calculate? Hello! I have built this schematic: On the schematic, there's 6SL7GT, but I used ECC85. How can I calculate the voltage-gain of this stage? Thanks in advance! __________________ Best regards, Danko
 20th October 2005, 11:29 PM #2 diyAudio Moderator     Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1 The gain will be one-half that of the same circuit in grounded cathode. Gain = muRp/2(Rp + rp), where Rp is the plate load resistor and rp is the plate resistance. __________________ "Cities are globs. Globs are bubbling collections. Bubbling collections are hurricanes of the dead and the living all blasting subliminal stories lost in the nether of breezes."
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Join Date: Apr 2004
Location: Philly
Quote:
 Originally posted by SY The gain will be one-half that of the same circuit in grounded cathode. Gain = muRp/2(Rp + rp), where Rp is the plate load resistor and rp is the plate resistance.
WOW! That is the most concise explaination of LTP gain calculation that I have ever heard. Good one!
__________________
Heghlu'meH QaQ jajvam!

 21st October 2005, 01:06 AM #4 diyAudio Moderator     Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1 Well, to be fair, what I said is only true for very long tails like current sources. But for a tail of 47K in this circuit, it will be close. __________________ "Cities are globs. Globs are bubbling collections. Bubbling collections are hurricanes of the dead and the living all blasting subliminal stories lost in the nether of breezes."
 21st October 2005, 06:20 AM #5 diyAudio Member     Join Date: Jul 2004 Location: Ardeche As a rule of thumb: µ/4 You may have good surprise Yves.
 21st October 2005, 06:37 AM #6 diyAudio Member   Join Date: Apr 2004 Location: Hungary Thank you SY! Oh, thanks for mentioning current source! Wich parameters will (will?) improve of the LTP, if I use a LTP in the "tail" of the LTP, instead of a resistor? And also thank you, Yvesm! I have surprised! :-)) __________________ Best regards, Danko
 21st October 2005, 11:20 AM #7 diyAudio Moderator     Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1 There are a lot of good current source circuits floating around. Morgan Jones shows both bipolar and tube versions in "Valve Amplifiers." Gary Pimm has some more exotic examples on his web site. In the one long tailed pair amp I have at the moment (a rebuilt Eico HF87), I used a pretty simple cascode bipolar sink. The performance is excellent and it cost only a couple of dollars in parts. If it's possible for you to use a small negative supply (say, -12V or so), you can greatly simplify your circuit and improve the balance by using a CCS tail. __________________ "Cities are globs. Globs are bubbling collections. Bubbling collections are hurricanes of the dead and the living all blasting subliminal stories lost in the nether of breezes."
 21st October 2005, 12:48 PM #8 diyAudio Member   Join Date: Apr 2004 Location: Hungary Thanks! I will search google for some good performing CCS. __________________ Best regards, Danko
 21st October 2005, 07:58 PM #9 diyAudio Member   Join Date: Apr 2004 Location: Hungary Why do people mostly use semiconductor CCS, and not tube-CCS? I have seen many tube-amplifier schematics, but just a few of them use tube based constant current source. Is it only, becouse of a MJE340, or BC546 is far more cheaper than a tube? __________________ Best regards, Danko
 21st October 2005, 08:21 PM #10 diyAudio Member     Join Date: Apr 2004 Location: Philly As a side note, if you use the tail resistor instead of a CCS, don't forget that the sum of the 2 tube's current across the tail will eat your voltage at the plates down by it's value. It's an obvious mistake that I made once and plotted my loadlines about 60v too high, had quite a surprise when I built the thing up and tested it. __________________ Heghlu'meH QaQ jajvam!

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