
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
21st October 2005, 09:57 PM  #11  
diyAudio Member

Quote:


21st October 2005, 10:00 PM  #12  
diyAudio Moderator

Quote:
For all of that, some people love 'em and use 'em.
__________________
“A philosopher is a blind man in a dark room looking for a black cat that isn't there. A theologian is the man who finds it.”  Mencken 

22nd October 2005, 07:20 AM  #13  
diyAudio Moderator Emeritus
Join Date: Jan 2004
Location: Jakarta

Quote:
I've found a 6AU6 pentode to be easy to use and effective as a CCS, in the tail of a 6SL7 LTP which has its grounded grid at true ground (0v). My negative rail is 110v. I make sure the heater of the 6AU6 is at a safe voltage that doesn't exceed the rated heatercathode voltage limit 0f 100v. Current per triode in the LTP is 0.8mA, which means the plate current of the 6AU6 is 1.6mA. Voltage from 6AU6 plate to cathode is 112v, screen to cathode is 95v. If you look at the 6AU6 plate curves for screen voltage ~100v, you will see that they are very flat for such a low current. The plate current appears to be constant within 0.01%. For more current, e.g. as a CCS for a 6SN7 LTP, a negative rail of 150v would be preferable. 

22nd October 2005, 04:47 PM  #14  
diyAudio Member
Join Date: Apr 2004
Location: Philly

Re: LongTailedPair gain > how to calculate?
Quote:
"Differential amplifier (phase splitter etc) made from a 12AX7. The plate load resistors are 150k each, and the next stage grid resistors are 220k. The cathodes are tied together and fed from a 2 mA current source. What is the gain from either input to either output? Solution: Effective Plate Resistance = 71k (plate resistance for these bias conditions) paralleled by 150k, paralleled by 220k or about 39k. Effective cathode resistance. The current source is assumed to have a very high resistance, so may be neglected. Each cathode is "looking at" the other cathode. The gm under these bias conditions is about 1400 umhos (710 ohms). Therefore the cathode resistance is 710 + 710 or about 1420 ohms. Stage gain = 39000/1420 = 27.5. Note that the differential gain (one input to both outputs) is double this (55), since equal and opposite output is provided by each plate. This method also works for sand state devices as well."
__________________
Heghlu'meH QaQ jajvam! 

Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
How to calculate gain and output impedance?  RogerGustavsson  Solid State  1  7th June 2008 06:09 PM 
How to calculate gain?  lumanauw  Solid State  10  29th July 2007 01:57 AM 
Have to calculate gain for typical small JFET preamplifier  supernet  Solid State  4  12th August 2006 12:22 AM 
How to calculate the gain of an inputdriver stage?  Antonio Tucci  Tubes / Valves  0  8th October 2004 01:25 PM 
New To Site?  Need Help? 