Looking for Transistor based Gyrator info. Any "Wireless World" collectors out there? - Page 3

Pjotr · 13th December 2008, 01:35 PM

Normal vacuum tube filaments are designed to be driven by a voltage source. Their dynamic impedance is fairly high, that is, the current does not change much with varying voltage. Driving it by a current source gives unreliable heating power. Only filaments designed for series power (like in direct mains powered TV sets) will do proper driven from a current source.

Just my 2Ct

Hearinspace · 13th December 2008, 11:45 PM

Quote:

Originally posted by Pjotr
. . . . . .Driving it by a current source gives unreliable heating power. Only filaments designed for series power (like in direct mains powered TV sets) will do proper driven from a current source.

Just my 2Ct

Hi Pete !
What you're saying is interesting , but it makes it curious that the verdict from those who have powered tube heaters and filaments from both Voltage and Current regs is almost unanimously in favour of Current regs. If you are correct (and I don't doubt you are) then I wonder if the two things are unrelated and current regs sound better for a different reason.

Pjotr · 14th December 2008, 10:48 AM

Hi,

For that your reasoning is probably right

At low frequencies the filament supply should behave as a voltage source to ensure proper heating power. But the thermal time constant of the filament is pretty long, especially with indirect heated tubes. So the voltage source behaviour is not needed at higher frequencies and indeed an inductor in series will isolate the supply the higher the frequency goes.

I have no real experience how this will sound but my proposal is: Make a regulated supply and make the gain of the control loop dropping down with frequency. This will simulate a psu with inductive behaviour. You can make the frequency corner of the control loop quite low, but if you make is too low you get overshoot and instability at start up.

jkeny · 7th February 2009, 01:39 PM

Guys,
Is this a real gyrator then? I'm looking to drop about 10V from a 72V DC for use in a 150W amp. I considered the gyrator as a way to do this & get ripple reduction while I'm at it. I just put an additional 12 V zener (1N4742) in there to act as a regulator also.

korneluk · 19th February 2011, 07:58 PM

Here's another example:

For the full text and explanation follow the link:
Capacitance Multiplier Power Supply Filter

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13th December 2008, 01:35 PM	#21
Pjotr diyAudio Member Join Date: Nov 2002 Location: Netherlands	Normal vacuum tube filaments are designed to be driven by a voltage source. Their dynamic impedance is fairly high, that is, the current does not change much with varying voltage. Driving it by a current source gives unreliable heating power. Only filaments designed for series power (like in direct mains powered TV sets) will do proper driven from a current source. Just my 2Ct

14th December 2008, 10:48 AM	#23
Pjotr diyAudio Member Join Date: Nov 2002 Location: Netherlands	Hi, For that your reasoning is probably right At low frequencies the filament supply should behave as a voltage source to ensure proper heating power. But the thermal time constant of the filament is pretty long, especially with indirect heated tubes. So the voltage source behaviour is not needed at higher frequencies and indeed an inductor in series will isolate the supply the higher the frequency goes. I have no real experience how this will sound but my proposal is: Make a regulated supply and make the gain of the control loop dropping down with frequency. This will simulate a psu with inductive behaviour. You can make the frequency corner of the control loop quite low, but if you make is too low you get overshoot and instability at start up.

19th February 2011, 07:58 PM	#25
korneluk diyAudio Member Join Date: Jan 2005 Location: South Florida	Here's another example: For the full text and explanation follow the link: Capacitance Multiplier Power Supply Filter

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