Hi,
You do not need to have exactly 6.3 VDC on the heaters.
A (maximum) margin of 5% is allowed at either end meaning you can reduce the heater voltage by 3,15V or up it by the same amount without affecting the tube's life expectancy or overall functionality in any way.
Any 7806 type reg. of sufficient current capacity would just fine.
Cheers,
You do not need to have exactly 6.3 VDC on the heaters.
A (maximum) margin of 5% is allowed at either end meaning you can reduce the heater voltage by 3,15V or up it by the same amount without affecting the tube's life expectancy or overall functionality in any way.
Any 7806 type reg. of sufficient current capacity would just fine.
Cheers,
That's why I propose a low dropout regulator, 4.27 V is far out of specs, unless you want work with starved heaters.
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For voltages you get, the transformer secondary only has 6 - 0 - 6 VAC instead of 6V3 - 0 - 6V3
V(Out)=6*√2-0.7-3=4.78 V
With an LT1085 you can get
V(Out)=6*√2-0.7-1.5=6.28 V
The difference from measurements may be due to dropout in the diodes, try Schottky rectifiers.
Edit: Don't forget to elevate heater voltage to ground, something about 65 V for 250 B+
V(Out)=6*√2-0.7-3=4.78 V
With an LT1085 you can get
V(Out)=6*√2-0.7-1.5=6.28 V
The difference from measurements may be due to dropout in the diodes, try Schottky rectifiers.
Edit: Don't forget to elevate heater voltage to ground, something about 65 V for 250 B+
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Here, page 1 in datasheet
http://www.google.com.ar/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CC0QFjAA&url=http%3A%2F%2Fwww.linear.com%2Fdocs%2F3741&ei=z8TKUt2yNpSssQSZioGIDw&usg=AFQjCNE8-DSdhVtLg7527HpB0xFgb3dF6g&sig2=2Ip0z0JIiCHqYNHwXzXc1g&bvm=bv.58187178,d.cWc
SR260 seems too weak, try something like MBR1045
http://www.google.com.ar/url?sa=t&r...kwa5u0JGkX0X0dg&bvm=bv.58187178,d.cWc&cad=rja
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Most people likes mains frequency and its harmonics, if it's your case go with AC.
Maybe the OP has another source from hum, but DC heaters is a good start.
I have only ever used DC in my phono design for the first stage. All my other line level preamps use AC heaters and they are whisper quiet. Heater lead dressing, elevated ground reference (+20VDC) and strict hierarchical star grounding is all it takes. Easy.
Its not important - but its worth stating that it can be done relatively easily.
Shoog
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I have this exact same preamp, sat in a box waiting for me to 'finish' it. I've been meaning to dig it out lately; guess this thread leaves me with no excuses
There are several variations available, and some do use only AC heaters IIRC. I wonder why they opted for DC with this version..
Read somewhere that the pin arrangement on the 6n3p/5670 is well suited to minimising AC heater hum.
There are several variations available, and some do use only AC heaters IIRC. I wonder why they opted for DC with this version..
Read somewhere that the pin arrangement on the 6n3p/5670 is well suited to minimising AC heater hum.
Indeed DC heater supply, if well designed, is intrinsically superior.
Powering heaters with AC, hum is introduced to the grid by different mechanisms:
1) Induction due to the magnetic field of the heater
2) Through the capacitance between cathode and heater Ckf
3) Through the resistance between cathode and heater Rkf
4) Through a junction diode between cathode and heater
To reduce induction, a specially designed heater is necessary, only a few valves have. Twisting the wires only attenuates the external field.
Depending on the valve, capacitive coupling of hum can be small.
Rkf usually can't be found in datasheets, but for a E180F Rkf(min)=4MΩ at Vkf=60 V. Roughly calculation as triode connected CC yields Vhum≈50 mV, datasheet says Vhum≈5 mV (grounded heater)
Diode effect can be reduced elevating heater respect to cathode.
Even when not audible, hum is manifested in the FFT as two peaks of intermodulation at f(mains) and 2f(mains)
Most people like this, I don't.
An inaudible source of interference is still inaudible. If there is no hum waveform on the output it ain't there - fullstop. DC is not intrinsically superior - unless it is necessary to solve a specific problem.
You don't have to like something with no effect to think its not worth bothering about.
As I said, its the builders choice what he chooses to spend his time on, but time spent perfecting general build skills will be far more rewarding since if there are issues of hum - even with DC heaters they are impacting the performance of the circuit far more than AC heaters ever could.
Shoog
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Little difference, not audible as hum, but a coloration that people describe mostly as "warmth sound"
If FFT shows hum, at the output it must be measurable.AFAIK
What specific problem? Hum perhaps?
Little difference, not audible as hum, but a coloration that people describe mostly as "warmth sound"
If FFT shows hum, at the output it must be measurable.AFAIK
What specific problem? Hum perhaps?
Exactly that inaudible/unmeasurable stuff.
I am going to leave this now, my point has been stated and its up to the builder whether he builds to avoid the issue or not.
Shoog
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Today i replaced the 47uF BC/vishay parallel with x2 10uF MKPs to
4x10uF + 4x10uF, the two wima 2,2uF mkp before choke i didn't touch,
It made a HUGE difference in SQ, more then changing a wima mks for an mundorf SIO for example so happy there BUT
HUM get much worse... very low freq and almost i'm thinking a truck goes by my house when it's powered on. Only that it's constant
Do i need to beef up capacitance more... like Carl said.. should i add more on the last cap(s)?? Like 47uF extra or something?
I don't won't to blow any rectifier though...
4x10uF + 4x10uF, the two wima 2,2uF mkp before choke i didn't touch,
It made a HUGE difference in SQ, more then changing a wima mks for an mundorf SIO for example so happy there BUT
HUM get much worse... very low freq and almost i'm thinking a truck goes by my house when it's powered on. Only that it's constant
Do i need to beef up capacitance more... like Carl said.. should i add more on the last cap(s)?? Like 47uF extra or something?
I don't won't to blow any rectifier though...
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