I am building a VTV Octal Preamp. I followed the schematics, and need to figure out what I'm doing wrong. I'm using a Hammond 370BX PT instead of of the 270. Because I need the multiple inputs to wire for my mains voltage of 230VAC.
I have 2 of 370BXs. So I was able to compare them to each other.
Using a Variac & Dim Bulb (40WATT)
Dim bulb will glow a little brighter than I expected because of filaments?
When testing the power supply assembled:
With out Rect. tube: No glowing of Dim Bulb.
Pins 4 - 6 (584VAC)
Pins 2 - 8 (5.31VAC)
Green wires (6.7VAC)
With Rect. tube: Glowing of Dim Bulb. Not really bright.
Pins 4 - 6 (4VAC)
Pins 2 - 8 (1.85VAC)
Green wires (2.62VAC)
A & B leading out of Power supply ( 9VDC)
Michael
I have 2 of 370BXs. So I was able to compare them to each other.
Using a Variac & Dim Bulb (40WATT)
Dim bulb will glow a little brighter than I expected because of filaments?
When testing the power supply assembled:
With out Rect. tube: No glowing of Dim Bulb.
Pins 4 - 6 (584VAC)
Pins 2 - 8 (5.31VAC)
Green wires (6.7VAC)
With Rect. tube: Glowing of Dim Bulb. Not really bright.
Pins 4 - 6 (4VAC)
Pins 2 - 8 (1.85VAC)
Green wires (2.62VAC)
A & B leading out of Power supply ( 9VDC)
Michael
Attachments
Parafeed813 , dexiotropic
All CTs are grounded. 50volt Bias tap is isolated. Any input wires on the primary side not used are individually isolated.
All CTs are grounded. 50volt Bias tap is isolated. Any input wires on the primary side not used are individually isolated.
The centre tap of the 5v filament supply should not be grounded, isolate it from everything else. It has full B+ on it, and you are connecting this to ground - it’s shorted.
1.) Why not use centre trap of 5V AC (yellow/black) as output of rectifier tube (connected to 100R resistor)?
2.) Are you sure, that in amplifier the blue (why blue? In the accepted colour coding this colour reserved for negative voltages) wire bus ( B+ ) and grey wire bus ( 0V, "ground" ) NOT connected together?
2.) Are you sure, that in amplifier the blue (why blue? In the accepted colour coding this colour reserved for negative voltages) wire bus ( B+ ) and grey wire bus ( 0V, "ground" ) NOT connected together?
Attachments
1) I didn't know you could do that. Is there any benefit to doing that? Other than just isolating it.
2) The Blue & Gray are not connected. The Gray wire (Ground) is running under.
Thanks, Michael
If you use DH rectifier tube, the correct balancing of its filament (as cathode) sides (potential and AC hum) difference is the centre trapped filament coil.
It it available, use it.
It it available, use it.
I would like to thank everyone for the help!
B+ is stable at 331VDC to both channels under load. Even without the DC rectification of the 6.3 filament voltage it is dead quite. I have no hum that I can hear. It's been burning in for the last half hour. Will continue to burn it in the rest of the afternoon before I put the bottom plate on.
Michael
P.S. Thanks---euro21
I used the CT to the 100K resistor to the cap.
B+ is stable at 331VDC to both channels under load. Even without the DC rectification of the 6.3 filament voltage it is dead quite. I have no hum that I can hear. It's been burning in for the last half hour. Will continue to burn it in the rest of the afternoon before I put the bottom plate on.
Michael
P.S. Thanks---euro21
I used the CT to the 100K resistor to the cap.
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