Tube Rectifier protection

gingertube · 14th February 2008, 02:58 AM

I'm sure this has been covered before but I could'nt find it.

I have a 5R4 => 2uF polypropylene => 8H => 100uF power supply in a 6V6 Push Pull Amp. That is, it is almost a choke input supply.

At switch on I occassionally see arcing in the 5R4. I seem to recall someone suggesting protecting of tube rectifiers against start up arcs by adding solid state diodes.
Should there be a diode in series with each tube recifier anode, a single diode in the tube rectifier output or what?

Any advise gratefully received.

Thanks,
Ian

GK · 14th February 2008, 04:30 AM

These are the diodes you want:

http://au.farnell.com/jsp/search/res...isGoback=false

Just put one with an appropiate clamping voltage in parallel with your rectifier.
It will clamp the voltage to a safe maximum and conduct the excess transient current.

Sheldon · 14th February 2008, 04:48 AM

I don't know if this is relevant, but some of the 5R4 data sheets suggest limits on the current and voltage prior to the rectifier filament heating up; http://www.tubezone.net/pdf/5r4.pdf

Try modeling your supply in PSUD. You may find that the initial conditions (first few cycles at the rectifier) exceed the limits. I don't know if protection diodes would help here, as I would guess this is a forward conduction issue (but I'd be curious to hear a learned opinion). Maybe a current limiting thermistor on the primary, to keep the initial current peaks below the threshold?

Sheldon

ray_moth · 14th February 2008, 06:43 AM

You don't say anything about your power transformer. According to data I've seen, the 5R4 needs at least 250 ohms in series with each plate. If your OPT has less resistance than that, in each half of the secondary, you could try adding a resistor in series with each plate to make up the difference.

coolmaster · 14th February 2008, 07:21 AM

Same topic here:

GZ34 anode load resistor calculation - help?

GK · 14th February 2008, 09:28 AM

Quote:

Originally posted by G.Kleinschmidt
These are the diodes you want:

http://au.farnell.com/jsp/search/res...isGoback=false

Just put one with an appropiate clamping voltage in parallel with your rectifier.
It will clamp the voltage to a safe maximum and conduct the excess transient current.

Woops.
Sorry, my brain wasn't engaged here. You need to connect the transil diode in series, back to back with a p-n diode for the protection of a tube rectifier.
I was thinking of protecting series pass tubes in power supplies.

14th February 2008, 02:58 AM	#1
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	Tube Rectifier protection I'm sure this has been covered before but I could'nt find it. I have a 5R4 => 2uF polypropylene => 8H => 100uF power supply in a 6V6 Push Pull Amp. That is, it is almost a choke input supply. At switch on I occassionally see arcing in the 5R4. I seem to recall someone suggesting protecting of tube rectifiers against start up arcs by adding solid state diodes. Should there be a diode in series with each tube recifier anode, a single diode in the tube rectifier output or what? Any advise gratefully received. Thanks, Ian

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14th February 2008, 04:30 AM	#2
GK Account disabled at member's request Join Date: Jan 2006	These are the diodes you want: http://au.farnell.com/jsp/search/res...isGoback=false Just put one with an appropiate clamping voltage in parallel with your rectifier. It will clamp the voltage to a safe maximum and conduct the excess transient current.

14th February 2008, 04:48 AM	#3
Sheldon diyAudio Member Join Date: Dec 2003 Location: San Diego	I don't know if this is relevant, but some of the 5R4 data sheets suggest limits on the current and voltage prior to the rectifier filament heating up; http://www.tubezone.net/pdf/5r4.pdf Try modeling your supply in PSUD. You may find that the initial conditions (first few cycles at the rectifier) exceed the limits. I don't know if protection diodes would help here, as I would guess this is a forward conduction issue (but I'd be curious to hear a learned opinion). Maybe a current limiting thermistor on the primary, to keep the initial current peaks below the threshold? Sheldon

14th February 2008, 06:43 AM	#4
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	You don't say anything about your power transformer. According to data I've seen, the 5R4 needs at least 250 ohms in series with each plate. If your OPT has less resistance than that, in each half of the secondary, you could try adding a resistor in series with each plate to make up the difference.

14th February 2008, 07:21 AM	#5
coolmaster diyAudio Member Join Date: Jul 2005 Location: MY	Same topic here: GZ34 anode load resistor calculation - help?

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