Just a couple of questions for the gurus and those with experience...
1. What transformers do you use in when you make your prototypes? Do you have one for each tube application or do you have a multipurpose transformer with 'multiple taps' (is there such a thing?) in your test bench?
2. What sort of internal modifications and parts are needed if:
a. I wish to change the driver tubes in my integrated amp from 12ax7 to 6sn7? 6sl7? Do I need a new transformer or is there a workaround in correcting the necessary voltages/current etc?
b. earphone out
c. passive/active preamp section?
3. Related to question #2, would the unit need lesser modifications if I plan to use 12sn7 instead?
4. On Chokes:
What do I look for when buying a used choke if I plan to use it on a preamp project for a 12ax7 family? for the 6sn7 variant? Is there a choke rating similar to transformer rating (xvolts-0-xvolts)?
Thanks.
1. What type of transformer? Power? Output? My amp prototyping chassis use Hammond 125ESE (from
www.angela.com) output transformers due to the multiple primary/secondary connections I can use. The power transformer is sort of a "universal" type with several taps.
2a. Many factors have to be considered which will include the physical (octal vs. 9-pin), filament voltage/current, biasing, gain, drive capability, plate resistance, voltage and current issues. For example, the 12AX7 has a gain of 100 while the 6SL7 is 70.
2b. Use an impedance matching transformer for your headphone via the speaker output.
2c. in a passive mode, you feed the driver tube directly from a volume potentiometer. Depending on the circuit, you will have input impendance issues to consider.
3. 12SN7 is simply a 12.6V version of 6SN7
4. You need to determine the inductance, current capacity and DC resistance for you circuit. The rating is given as henry (inductance), mA (current), and DCR (impedance ). Example is 10H, 100mA, 100ohm DCR.