Fixed bias of any type is liable to make tubes draw different currents.
In a cathode bias (resistor) the resistor adjusts the bias voltage within a range to get approximately the same current all the time (if the current goes up the bias voltage goes up and switches the valve off slightly so bringing the current down).
There is no self compensation mechanism with fixed bias such as a diode since the bias voltage cannot alter with current variation. This is generally not a significant problem but will means that the two channels will not draw the same current and the divergence may increase over time.
I wouldn't worry about it unless one of the valves starts redplating.
Congratulations on getting it this far - does it sound as good as you remember it and did you get rid of the last of the hum ?
Shoog
In a cathode bias (resistor) the resistor adjusts the bias voltage within a range to get approximately the same current all the time (if the current goes up the bias voltage goes up and switches the valve off slightly so bringing the current down).
There is no self compensation mechanism with fixed bias such as a diode since the bias voltage cannot alter with current variation. This is generally not a significant problem but will means that the two channels will not draw the same current and the divergence may increase over time.
I wouldn't worry about it unless one of the valves starts redplating.
Congratulations on getting it this far - does it sound as good as you remember it and did you get rid of the last of the hum ?
Shoog
Yes i notice that whenever i adjusted the dropres, voltage was rockstable over those diodes..
Duncans gave me about 280V, real world was about 253V so had to lower dropres to half = 2,5K.
It sounds better then i can remember. Sound is calm, but bites when it should. Before it was more aggressive. I hear the studio/recording room very very well now even on old recording i thought i knew well. Now i have strong, solid and very deep bass too. It's very balanced from top to bottom. It's sum is impressing. I'm happy.
Hum.. first it was dead silent (i thought) but now when it's silent outside i can hear a small hum. I think it's little bit worse since old build. I can't hear it in listening position but a meter away it's there. I rally don't know where it can come from this time but yes it can be "everything" actually--not much space inside. I need to buy more cable for low level and twist. Some low level signal going down to sockets untwisted (not a pair)
I used Ölflex 2x1mm screened mainscable with extra coppertape on outside connected to earth, same with choke.
I heard that or read somewhere it can also be that the CT is not in the "middle" for filament. Didn't measure it but 300 sec was not "even" i recall.
Temp is now little higher:
Rectifier around 80 and the others around 90 degrees
Duncans gave me about 280V, real world was about 253V so had to lower dropres to half = 2,5K.
It sounds better then i can remember. Sound is calm, but bites when it should. Before it was more aggressive. I hear the studio/recording room very very well now even on old recording i thought i knew well. Now i have strong, solid and very deep bass too. It's very balanced from top to bottom. It's sum is impressing. I'm happy.
Hum.. first it was dead silent (i thought) but now when it's silent outside i can hear a small hum. I think it's little bit worse since old build. I can't hear it in listening position but a meter away it's there. I rally don't know where it can come from this time but yes it can be "everything" actually--not much space inside. I need to buy more cable for low level and twist. Some low level signal going down to sockets untwisted (not a pair)
I used Ölflex 2x1mm screened mainscable with extra coppertape on outside connected to earth, same with choke.
I heard that or read somewhere it can also be that the CT is not in the "middle" for filament. Didn't measure it but 300 sec was not "even" i recall.
Temp is now little higher:
Rectifier around 80 and the others around 90 degrees
Above pic on psu is not entirely correct
Dropres is 2,55k instead of 5,1k and last is 500R instead of 1k to get desired 280V. Last rc-filter is split (2x15uf and 2x1k) caps soldered direct on pins nr 4 (b+)
I put 2x165R (2x330r =6w para) bedore fuses on each 'leg' on sec. With 5v4-g it can be lower, maybe 100R instead.
Dropres is 2,55k instead of 5,1k and last is 500R instead of 1k to get desired 280V. Last rc-filter is split (2x15uf and 2x1k) caps soldered direct on pins nr 4 (b+)
I put 2x165R (2x330r =6w para) bedore fuses on each 'leg' on sec. With 5v4-g it can be lower, maybe 100R instead.
I owned a Krell kav300 and a krell krc-3 preamp some yrs ago. I have to say i have a better preamp today and with better bass (quantity and quality). And cheaper! 
but no, a behringer classD amp is not better then a kav300
The difference now to my yamaha are ridicilous. Yamaha sound like 99e boombox some built in loudness to i noticed now.. Fun to go back n listen old stuff to check my ears
but no, a behringer classD amp is not better then a kav300The difference now to my yamaha are ridicilous. Yamaha sound like 99e boombox
some built in loudness to i noticed now.. Fun to go back n listen old stuff to check my ears
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Guys...
Yesterday when I finally turned off my "little baby pre" It came out some "tink, tink, tink" like clicks many seconds after, clearly heard in speakers! I got little bit scared actually.
What can that be? Never heard that before.
Today I'm gonna measure my filament and see if CT is in the middle. Maybe also do some new twisted cable. Let's see. Also a pic from inside?
Could really fun if someone else build this too. Any questions? Just ask, here or via private messages
Yesterday when I finally turned off my "little baby pre"
It came out some "tink, tink, tink" like clicks many seconds after, clearly heard in speakers! I got little bit scared actually. What can that be? Never heard that before.
Today I'm gonna measure my filament and see if CT is in the middle. Maybe also do some new twisted cable. Let's see. Also a pic from inside?
Could really fun if someone else build this too. Any questions? Just ask, here or via private messages
Glass contraction and valve microphonics. Nothing to worry about.Guys...
Yesterday when I finally turned off my "little baby pre"
What can that be? Never heard that before.
Today I'm gonna measure my filament and see if CT is in the middle. Maybe also do some new twisted cable. Let's see. Also a pic from inside?
Could really fun if someone else build this too. Any questions? Just ask, here or via private messages
Shoog
And now there is more hum.... also lower in freq. not much more 1-2db? But still, i thought this was gonna be an small improvement the other direction.
I tried to measure my 3,15-0-3,15 on pt but i guess my meter is not up to the task. Very low ohm.
Hum/noise are equal in both channels.
I tried to measure my 3,15-0-3,15 on pt but i guess my meter is not up to the task. Very low ohm.
Hum/noise are equal in both channels.
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