Hi DF96
Sorry for being vague, let me explain in more detail. The ground bus starts at the diodes and goes on to first 50uf cap (bridged with resistor) on to second cap 500uf and further on to 50uf double cap (closest to amp stage) to end at star ground. The bus goes directly from point to point. The bias supply has a own lead to star ground.
I did one moore thing this time before powering up and this was to disconnect the volume potentiometer. I did this to eliminate if any problems where in that region.
The search goes on.........
Cheers
H00hbt try to disconect Main transformer electrostatic shield from the ground point.(Top Metal plate)
BTW I dont see in your PSU schematic third Main ground lead conected to AMP chasis Top metal plate, but only two 230V/AC wires conected to Main Trans. over the Main switch.
Think to operate Tube Amps Without proper Main ground lead conected to metal chasis is Dangerous for Amps operator.(or anybody else)
Best Regards
BTW I dont see in your PSU schematic third Main ground lead conected to AMP chasis Top metal plate, but only two 230V/AC wires conected to Main Trans. over the Main switch.
Think to operate Tube Amps Without proper Main ground lead conected to metal chasis is Dangerous for Amps operator.(or anybody else)
Best Regards
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DF96
Yes, maybe this is a solution.
Original schematic:
Modified schematic:
I have more voltage than in the original 370V vs 390V and at 0,5 A
Just clutching the straws.......
Cheers
H00hbt try to disconect Main transformer electrostatic shield from the ground point.(Top Metal plate)
BTW I dont see in your PSU schematic third Main ground lead conected to AMP chasis Top metal plate, but only two 230V/AC wires conected to Main Trans. over the Main switch.
Think to operate Tube Amps Without proper Main ground lead conected to metal chasis is Dangerous for Amps operator.(or anybody else)
Best Regards
Hello banat
I have main ground from PX to chassis, green and yellow lead in picture.
Cheers
I think you swapped the diagrams! The modified one looks OK, except you show the ground connection by the first capacitor instead of the last one.
Your description sounds OK, except what about the other channel? Do you have a PSU ground bus down the middle of the chassis (as shown in the diagram), with connections branching off to each capacitor?
Can you look at the output with a scope? Is it hum or buzz?
Your description sounds OK, except what about the other channel? Do you have a PSU ground bus down the middle of the chassis (as shown in the diagram), with connections branching off to each capacitor?
Can you look at the output with a scope? Is it hum or buzz?
No, the top diagram is actually from the original designer "triode Dick". The posters version is the one with the problems.
Sheldon
http://www.triodedick.com/Bill/schema_voeding.GIF
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h00hbt,
It's imprecise but pretty typical, to use the same symbol for safety earth and common. It's also pretty typical to show multiple earths or commons, and leaving it to the viewer to guess how they are connected.
I'm always careful about how I do the commons and earth, because I hate hum. My hearing ain't what it used to be, but I can hear that. Also, it bugs me, because it's always a sign of poor design or execution. I recently built a phono amp, and any errors there will definitely cause hum. Therefore, I was careful to draw up a schematic which accurately shows the connections and how they are wired. I'll be presumptious and say that this is an example of what DF96 is looking for.
Note that the raw power supply is in a separate chassis from the regulator and amp. The safety earth is connected to the power supply chassis, which is then connected to the amp chassis. That is connected by a single wire to the amp star ground.
It's imprecise but pretty typical, to use the same symbol for safety earth and common. It's also pretty typical to show multiple earths or commons, and leaving it to the viewer to guess how they are connected.
I'm always careful about how I do the commons and earth, because I hate hum. My hearing ain't what it used to be, but I can hear that. Also, it bugs me, because it's always a sign of poor design or execution. I recently built a phono amp, and any errors there will definitely cause hum. Therefore, I was careful to draw up a schematic which accurately shows the connections and how they are wired. I'll be presumptious and say that this is an example of what DF96 is looking for.
Note that the raw power supply is in a separate chassis from the regulator and amp. The safety earth is connected to the power supply chassis, which is then connected to the amp chassis. That is connected by a single wire to the amp star ground.
Attachments
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DF96
No, I have wired the PS with a separate ground bus for each channel, just like in schematic.
Sorry, I havn´t a scope just multimeter.
Cheers
Haven't many of these Bills been built before? No need to redesign the power supply, and nothing wrong using two rectifiers in parallel. Your gnd bus is pretty solid.
Since you had a increase in hum when messing with the gnd connectinos, it seems obvious to keep looking into the gnd ckt.
Is the bias circuit on that circuitboard way up in the top corner? Isn't it rahter important that bias circuit is as close to the grid/cathode it is to control? Any chance of hum picked up on those long leads. Tho it shouldn't be a problem due to the nature of a symmetrical PP output canceling out such noise, but you never know...
Are the heaters for the output tubes floating as in the schem? Not that heaters on the output tubes should produce such hum, but by now you should try everything.
Have you tried to gnd the grids of the output tubes to see if the hum goes away? (Short to gnd with a capacitor to shunt AC to gnd). That way you can eliminate or determine the fault in the output stage.
Good luck, this can be frustrating...
Since you had a increase in hum when messing with the gnd connectinos, it seems obvious to keep looking into the gnd ckt.
Is the bias circuit on that circuitboard way up in the top corner? Isn't it rahter important that bias circuit is as close to the grid/cathode it is to control? Any chance of hum picked up on those long leads. Tho it shouldn't be a problem due to the nature of a symmetrical PP output canceling out such noise, but you never know...
Are the heaters for the output tubes floating as in the schem? Not that heaters on the output tubes should produce such hum, but by now you should try everything.
Have you tried to gnd the grids of the output tubes to see if the hum goes away? (Short to gnd with a capacitor to shunt AC to gnd). That way you can eliminate or determine the fault in the output stage.
Good luck, this can be frustrating...
Hi SemperFi
Yes, you are right, many have been built before and it seams that there isn´t alot of problems with the design in general. I guess I will just work my way up the line and through the amp and se if I can make something out. Does seam strange that the hum whent up after re-wiring the ground bus so maybe the answer is there somewhere. Might just try to ground the grids and se, what value and V cap would I use?
Thanx
Maybe easier to lift the coupling cap. If not the cap should be a value that will shunt the low freq hum to gnd, say 10uF.
WOOOOHOOOOO!!
NO HUM!! 0,0000VAC on both output terminals. Absolutly dead quiet. Sounds just great, a little held back and muffled like not quite burnt in, promissing though.
Don´t know what caused the hum probably a combination of things. I went through sirquit and all the solder joints and made new connections on several places to ground. The 6SN7 tube I used was really bad so I changed it.
Anyway, thank you all for your concern and good ideas, just shows what a great community this is.
Cheers
Now...MUSIC!!!!
NO HUM!! 0,0000VAC on both output terminals. Absolutly dead quiet. Sounds just great, a little held back and muffled like not quite burnt in, promissing though.
Don´t know what caused the hum probably a combination of things. I went through sirquit and all the solder joints and made new connections on several places to ground. The 6SN7 tube I used was really bad so I changed it.
Anyway, thank you all for your concern and good ideas, just shows what a great community this is.
Cheers
Now...MUSIC!!!!
Good - enjoy the music!
Later on, it might help if you rethink through what changes you made to fix it, and try to decide which particular change did the trick. In doing this you will learn more about grounding. People sometimes regard this as a black art, but in most cases it is simply applied physics!
Later on, it might help if you rethink through what changes you made to fix it, and try to decide which particular change did the trick. In doing this you will learn more about grounding. People sometimes regard this as a black art, but in most cases it is simply applied physics!
Hi DF96
I believe that good mechanical contact is crucial in all connections. I suspect that I maybe had a dodgy one or two.
I need to bias the tubes now, how do I do this? wich pinsdo i connect to the multimeter and how many mA should I have?
Thanks DF96 for you help
Cheers
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