Differential input stage in PP tube amps
"HpW-Works" wrote in message
...
Patrick,
Noticed an error in the MJE340 current source circuit in the first
schematic. (Correct in the others.)
why do you use only one transistor. Using two would also increase the
output impedance....
----------- V+
| |
R LOAD
| |
| C
--------B Q1
| E
C |
Q2 B--------
E |
| Re
| |
----------- GND
Yes, and one most likely does not need -45V rail. Q2 can be a 5-cent general
purpose like BC547. Resistor R can be connected to +B rail, not ro the load
(common cathodes).
This circuit has two disadvantages:
1) It may oscillate at dozens of MHz with certain unlucky combination of Q1
ans Q2;
2) Regulated current is temperature dependent -- drops as the temperature
rises.
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