I forgot something. With a 7F7 in the circuit, the two triodes will draw about 4mA. This means that my PSUD II simulation works at 280 Volts for the B+ for the 7F7. With a 7N7 in the circuit, the current draw will be higher, and the voltage will drop to around 240 Volts if the 7N7 is made to draw a total of 10mA, and around 195 Volts if it draws 16mA in total. What should I shoot for with respect to current draw for each 7N7 triode?
Final schematic and voltages of 7C5 amp
Hi All.
Attached is the final schematic with measured voltages for my 7C5 amp. I am very happy with the sound of this amp. It has the clear midrange and highs of my (now sold) 6V6 amp. It's bass response is much better than my previous 6V6 amp, but it still isn't a bass monster by any stretch. Other than that, it sounds great. It seems that the switch to go from 7F7 to 7N7 will not be used as, in comparison, the amp sounds dull and lifeless with a 7N7 in it. This may be due to my choice of a 100K plate resistor for both tubes. I would recommend that it would be best to build this amp as just a 7F7/7C5 amp. A 5K to 8 Ohm OPT would also work with a bit more distortion and a bit more output power. The power transformer is a 250 Volt @ 130 mA unit from an old console.
Hi All.
Attached is the final schematic with measured voltages for my 7C5 amp. I am very happy with the sound of this amp. It has the clear midrange and highs of my (now sold) 6V6 amp. It's bass response is much better than my previous 6V6 amp, but it still isn't a bass monster by any stretch. Other than that, it sounds great. It seems that the switch to go from 7F7 to 7N7 will not be used as, in comparison, the amp sounds dull and lifeless with a 7N7 in it. This may be due to my choice of a 100K plate resistor for both tubes. I would recommend that it would be best to build this amp as just a 7F7/7C5 amp. A 5K to 8 Ohm OPT would also work with a bit more distortion and a bit more output power. The power transformer is a 250 Volt @ 130 mA unit from an old console.
Attachments
Looks good! I need to grab some loctal tubes to play with at some point again.
For the 7N7/7F7 switch, honestly I would leave it as 7F7 too. the 7F7/7C5 (6SL7/6V6) pairing is pretty good, there's some sort of mojo there that's hard to explain. the 7N7 may want a 47k plate resistor here, but I wouldn't bother unless you have time to kill.
Power output is likely low, but linearity and damping factor are probably very good with such a high impedance output transformer. Just the ticket for efficient speakers
What enclosure is that? Almost looks like a toolbox. I like it.
For the 7N7/7F7 switch, honestly I would leave it as 7F7 too. the 7F7/7C5 (6SL7/6V6) pairing is pretty good, there's some sort of mojo there that's hard to explain. the 7N7 may want a 47k plate resistor here, but I wouldn't bother unless you have time to kill.
Power output is likely low, but linearity and damping factor are probably very good with such a high impedance output transformer. Just the ticket for efficient speakers
What enclosure is that? Almost looks like a toolbox. I like it.
Lingwendil: Thanks. The enclosure is an old file card box from the sixties. I’ve built a couple of amps using these boxes. The proportions are nice, but the hinged back makes them a little awkward for working in and wiring. Attached is a photo of a headphone amp I built into two of the same boxes, one for the power supply, and the other for the circuit. The other picture is an amp I built into a money lock box.
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.