06-03-2017, 06:30 AM
The saga of the amplifier continue's, though I've slain a few monsters I'm nowhere near taking on Grendel yet. In other words I've been having "fun" and games with the CCS for the LTP PS not made easier by a valve base going conductive hence the odd readings. I've also taken time off from this amp to do a bit of gardening when the sun shone.
The CCS circuit as attached in post #14 works alright, but I found getting R1 right so there is enough current to turn on the reference diodes is tricky. The circuit works a bit like a see saw I found with the values of R1 and R2/3 acting like weights I tried useing a 2V7 zener and green instead of LED 1, because the MJE340 datasheet says Vbe should be 3v. By using a 20k 10 turn pot as R1 I got the CCS to work. However someone over on UKVRR has helped by knocking up a far simpler CCS using 2 resistors, a zener and a MJE340.
I read up on CCS's as used in LTP tail's and CCS's in general and there seems two ways of going about this. You can use more complex circuits using more parts to ensure thermal stability, compliance and a higher impedance or use a low component count simple circuit. Last night my brain got a bit over heated and I had a brain wave of using a low wattage R or light bulb in thermal contact with a negative coifficient zener instead of R1 so as the reference diodes draws more current the neg co zener compensates. Combined with an avalanche zener as LED2 it would result in a very stable CCS. In the cold light of morning my instinct is to adhere to the advice of the acronym KISS.
As with any problem encountered in life, amp design or electronics design you have to be careful you don't go round in circles and disappear up your own arse I suppose. I spent a while trying to work out the impedance of various CCS circuits by using this beauty - R out = (h oe (Q 2))-1 + (R 2 R 3)h fe (Q 1)h fe (Q 2) . All well and good but what the hell does it mean ( is that R2 + R3 or R2 x R3? The former surely, same goes for Q1 hfe and Q2 hfe) and transistor data sheet's for the BC549 and MJE340 don't list hoe or hfe come to that. hFE yes, but not hfe.
Life was simpler for Beowolf, go to the hall, get drunk, get big sword and chop monsters head off, back to hall to get drunk with the lads. Andy.
The CCS circuit as attached in post #14 works alright, but I found getting R1 right so there is enough current to turn on the reference diodes is tricky. The circuit works a bit like a see saw I found with the values of R1 and R2/3 acting like weights I tried useing a 2V7 zener and green instead of LED 1, because the MJE340 datasheet says Vbe should be 3v. By using a 20k 10 turn pot as R1 I got the CCS to work. However someone over on UKVRR has helped by knocking up a far simpler CCS using 2 resistors, a zener and a MJE340.
I read up on CCS's as used in LTP tail's and CCS's in general and there seems two ways of going about this. You can use more complex circuits using more parts to ensure thermal stability, compliance and a higher impedance or use a low component count simple circuit. Last night my brain got a bit over heated and I had a brain wave of using a low wattage R or light bulb in thermal contact with a negative coifficient zener instead of R1 so as the reference diodes draws more current the neg co zener compensates. Combined with an avalanche zener as LED2 it would result in a very stable CCS. In the cold light of morning my instinct is to adhere to the advice of the acronym KISS.
As with any problem encountered in life, amp design or electronics design you have to be careful you don't go round in circles and disappear up your own arse I suppose. I spent a while trying to work out the impedance of various CCS circuits by using this beauty - R out = (h oe (Q 2))-1 + (R 2 R 3)h fe (Q 1)h fe (Q 2) . All well and good but what the hell does it mean ( is that R2 + R3 or R2 x R3? The former surely, same goes for Q1 hfe and Q2 hfe) and transistor data sheet's for the BC549 and MJE340 don't list hoe or hfe come to that. hFE yes, but not hfe.
Life was simpler for Beowolf, go to the hall, get drunk, get big sword and chop monsters head off, back to hall to get drunk with the lads. Andy.
