Hello friends.
I have a 300B SE amp. I am waiting for new Khozmo stepped attenuators. I put at first tube grid a 70k resistor, for use the amp without potentiometer and protect them a little. Know, i have 2kz noise at both speakers. I put a picture.
I have a 300B SE amp. I am waiting for new Khozmo stepped attenuators. I put at first tube grid a 70k resistor, for use the amp without potentiometer and protect them a little. Know, i have 2kz noise at both speakers. I put a picture.
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Are you sure, that measuring device working correctly? The whole spectrum is "slips up" 20-30dB as expected in "normal" amplifiers.
Try to use measuring with shorted input of FFT device. If its self noise is at about -100..130dB, the measuring set probably OK.
Schematic?
Try to use measuring with shorted input of FFT device. If its self noise is at about -100..130dB, the measuring set probably OK.
Schematic?
Use two different cell phones. I don't have instrumental. Noise is noticeable on tweeters. I don't have a good diagram.
Are you "measuring" with phone microphone????😳
The room background noise dominates, do this FFT is good only for indication, not measuring.
If you call noise in tweeter, probably the first stage is the source of trouble.
Are you use high gm tube without grid stopper?
Try tapping this tube.
The room background noise dominates, do this FFT is good only for indication, not measuring.
If you call noise in tweeter, probably the first stage is the source of trouble.
Are you use high gm tube without grid stopper?
Try tapping this tube.
I use the Russian 6E6P-DR tube in the first stage. Is a medium-high gm (approx 30) tube. At this moment without step attenuator the grid stopper resistor is 70kohms.
70k is the grid leak resistor.
Try to use 1k carbon comp resistor as grid stopper (from pin 2 to 70k grid leak resistor) or ferrite beads on BOTH wires near pins (except filament) as Ale suggested:
https://www.bartola.co.uk/valves/2018/04/02/6э6п-др-6e6p-dr-preamp-driver/
Look carefully the tube pins wiring in schematic.
Are you use one cathode resistor (and tied together pin 1-3) or use both cathode pins with individual resistors?
Are you use AC heating for this tube?
Try to use 1k carbon comp resistor as grid stopper (from pin 2 to 70k grid leak resistor) or ferrite beads on BOTH wires near pins (except filament) as Ale suggested:
https://www.bartola.co.uk/valves/2018/04/02/6э6п-др-6e6p-dr-preamp-driver/
Look carefully the tube pins wiring in schematic.
Are you use one cathode resistor (and tied together pin 1-3) or use both cathode pins with individual resistors?
Are you use AC heating for this tube?
Without grid leak resistor (or attenuator which is the "grid leak resistor") the tube will not working properly!
The grid must have DC ground via grid leak, else grid-cathode potential is indefinite, tube would ruining.
IMHO 70k is enormous as grid stopper.
If you not connected ALL pins as Ale described, the tube also not working well.
700K as the grid leak resistor is probably too high. The datasheet for the 6E6P-DR that I know doesn't state the maximum value for the grid leak resistor but the attached datasheet for the 6E6P-E states 500K as the maximum.
I advise you to use no more than 100K for the grid leak resistor (and use 1K for the grid stopper like euro21 already wrote).
I advise you to use no more than 100K for the grid leak resistor (and use 1K for the grid stopper like euro21 already wrote).
Really ? i have big capacitors an Cree diodes for filament supply heaters for de 45 and 300 tubes.
But i dont understand why the noise came up when i took out the stepper attenuator.
Post #6:
...ferrite beads on BOTH wires near pins (except filament) as Ale suggested:
https://www.bartola.co.uk/valves/2018/04/02/6э6п-др-6e6p-dr-preamp-driver/
...ferrite beads on BOTH wires near pins (except filament) as Ale suggested:
https://www.bartola.co.uk/valves/2018/04/02/6э6п-др-6e6p-dr-preamp-driver/
I put resistors of more reasonable values, 1k grid stopper , and 68k grid leak. goodbye to the noise.
I can't understand why some people who want to put the hand on a tube stuff doesn't have a decent test set.
It is easy to do, a good sound card, a good attenuator for signal in input and the use of Arta or Rew as software. So you will have a good generator and a good range of test for audio stuff
It is easy to do, a good sound card, a good attenuator for signal in input and the use of Arta or Rew as software. So you will have a good generator and a good range of test for audio stuff