After several false starts I have come back to this circuit for my latest preamp project. I have not been able to find the specification for the 6H30 that says what the heater voltage range is. I think the Russian language version says 6.3 +/- 0.9 volts. Does anyone know the range? The heater supply does not us any voltage regulation so the transformer sets it. With a 9.0v secondary I get 11.9 volts for two heaters in series. Is this too low? A 10v secondary results in 13 volts. I figured being under the specification was better then over for tube life.
Thanks John
Thanks John
Hi John
The 6H30 takes 6-6.6v on the heaters according to the datasheet. Are you not regulating this? IME regulation and especially current sourcing the heaters is quite beneficial for the sound. Setting the CCS requires some experimentation but will guarantee longer life and (possibly) better sound.
The 6H30 takes 6-6.6v on the heaters according to the datasheet. Are you not regulating this? IME regulation and especially current sourcing the heaters is quite beneficial for the sound. Setting the CCS requires some experimentation but will guarantee longer life and (possibly) better sound.
The 25mkII uses the +180v to bias the tube heaters to +70v. I assume this means that a regulator can not be used. If I am stuck with the transformer as the voltage regulator do I use 11.8v or 13v. So far these are my choices, unless someone knows where I can get a transformer that outputs 9.5 volts at 2 amps.
Thanks John
Thanks John
analog_sa said:
Yup.
johnmarkp, if the heater transformer secondary ouput is floating (i.e. not referenced to ground) then you can simply off-set ( / bias) it to +70 V whether it is regulated or not. When using a regulator the regulator references the return from the heater, not 'ground'. The whole regulated sub-system is floating and can hence be biased to any voltage you choose.
If you do go AC I would use the higher voltage and insert a resistor to drop the voltage to what you require.
Hello,
I need to finish the PCB :
http://svle.free.fr/webfiles/LS25.pdf
For the moment I use 250V cap because ARC use a such type but why ? No need to use as big capacitor in // of zener diode... I think 50V cap is enough.
I need to finish the PCB :
http://svle.free.fr/webfiles/LS25.pdf
For the moment I use 250V cap because ARC use a such type but why ? No need to use as big capacitor in // of zener diode... I think 50V cap is enough.
Going back to the original schematic and, in particular, R9 - this reminds me a lot of Nelson Pass SUSY circuit, where a diffamp has the sources separated by a resistor, and that can greatly reduce 3rd order harmonics (it will also change the gain).
So, when using other JFETs at the input, or modifying the bias point, or for tweaking the circuit in general it might be a good idea to change R9 while looking at THD at the output....
just an idea.....
So, when using other JFETs at the input, or modifying the bias point, or for tweaking the circuit in general it might be a good idea to change R9 while looking at THD at the output....
just an idea.....
Hello
Looking at schematic diagram there are four capacitors
at output C7//C9//C11//C13 0.01//0.68//4//4
Also found this info from
Audience auriCAP usa
Do not use bypass capacitors in the signal path. A single capacitor for DC blocking/AC
coupling creates a simple path with one time constant. The signal quality will be
compromised if a bypass or multiple bypass capacitors are added to a signal path capacitor.
Bypass capacitors were used in the past to bypass low quality film capacitors or electrolytic
capacitors. The bypass was the lesser of two evils. With the advent of better quality film
capacitors the need for a bypass capacitor was eliminated. Bypass capacitors create multiple signal
paths with multiple time constants. These time constants are very short but they can still be heard
as a smear or overall loss of focus.
Always bypass power supply capacitors. This maintains a low source impedance to the power supply
over a wide bandwidth. If budget and space permit it is good to use multiple value power supply
bypass capacitors with the smallest value being installed directly at the active device.
(Tube or transistor.)
What do you think about connecting a few capacitors // in
signal path ?
Thanks
Looking at schematic diagram there are four capacitors
at output C7//C9//C11//C13 0.01//0.68//4//4
Also found this info from
Audience auriCAP usa
Do not use bypass capacitors in the signal path. A single capacitor for DC blocking/AC
coupling creates a simple path with one time constant. The signal quality will be
compromised if a bypass or multiple bypass capacitors are added to a signal path capacitor.
Bypass capacitors were used in the past to bypass low quality film capacitors or electrolytic
capacitors. The bypass was the lesser of two evils. With the advent of better quality film
capacitors the need for a bypass capacitor was eliminated. Bypass capacitors create multiple signal
paths with multiple time constants. These time constants are very short but they can still be heard
as a smear or overall loss of focus.
Always bypass power supply capacitors. This maintains a low source impedance to the power supply
over a wide bandwidth. If budget and space permit it is good to use multiple value power supply
bypass capacitors with the smallest value being installed directly at the active device.
(Tube or transistor.)
What do you think about connecting a few capacitors // in
signal path ?
Thanks
Thanks Hollow Man but I still not.
For the moment I work on a D-Class amp from Tripath, a winding machine for making output transformers and a ECL82 driver for 845 push pull amp...
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