0Z4 (0Z4)substitute
0Z4 (0Z4)substitute
How would one go about making a solid state substitute for this rectifier tube, so that it could function with a vibrator in a car radio?
My understanding is, just placing diodes won't work with a vibrator.
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gas rectifier substitution
I dont agree with Your pessimism: I think that diodes would in fact do the job. They are rather unlimited compared with the restriction of a gas discharge rectifier. A gas rectifier needs a starter supply voltage, here it is specified with 300 volts per plate. Furthermore a minimum current is necessary to maintain the "arc". Here 30 ma DC output current is the specified minimum.
Diodes are free of all such limitations. Only max. current and peak inverse voltage have to be considered, thats all. Maybe a few hundred ohms in series to protect the vibrator contacts are advisable. 1N4007 or similar should be sufficient.
Have a try.
Good luck,
KoBi
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http://www.wps.com/archives/tube-datasheets/Datasheets/Raytheon-SP-7649-360-20M/4.JPG
and
http://www.wps.com/archives/tube-datasheets/Datasheets/Raytheon-SP-7649-360-20M/5.JPG
The 0Z4 drops about 24 volts at 110 mA. That means the tube has an effective series resistance of about 218 Ohms or so. This series resistance protects the vibrator (and the diodes) from excessive current as the polarity of the primary is switched back and forth.
Excessive current in the transformer secondary, either due to the diodes staying on* (See below), or charging current in the filter capacitor, will cause excess current to flow in the vibrator contacts, or switching transistors.
The problem with solid state rectifiers, and again, depending on which ones you use, is the reverse recovery time. 1N4000 series diodes were designed for 60 Hz sine wave rectification. They turn on slow and turn off slow. Minority carriers are what causes a diode to appear "still on" when the polarity reverses suddenly. In the case of a 1N4004 diode, this is greater than 2 uS.
If the "still on" time of the rectifiers is longer than the transition time of the wave form, both diodes appear to be "on"
at the same time. (Think shorted diode in a bridge rectifier.)
Mechanical vibrators have a small "both sides off" time as the armature transition from one contact to the other. Approximately 30 uS or so. Not all solid state vibrators have that feature. (Known as a guaranteed dead time.)
However, if the diode's "still on" time exceeds that "both sides off" time of either the solid state or mechanical vibrator, you will end up putting a temporary short across the transformer. This in turn beats the hell out of the vibrator contacts or the switching transistors in the mechanical vibrator.
Additionally, repeated stressing of the diodes like this will ultimately result in premature (and or sudden) failure of one or both diodes.
Putting some value of resistance in series with the diodes, and this means TWO resistors, one in series with each diode, limits the current that can flow with slower diodes. It also limits the charging current to the first filter capacitor.
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I appreciate and honor the theoretical considerations. But I think that the max.30µs of a diode (per specification) are short enough to limit the dangerous energy transfer during the transient phase to a bearable amount. And there is a choice of alternatives in the diodes sector. Only the 1N400x series are amongst the cheapest.
In the post war time numerous mechanical vibrators worked in combination with selenium rectifiers, which are not really fast switching devices.
And theoretically synchronous (self rectifying) vibrators should have never been used at all. There are phase shift problems between Xformer primary and secondary, which to a certain amount apply to our substitution as well.
The a.m. series resistors to the diodes are a must of course.
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snubbing capacitor
Hi,
what you ment as a snubbing cap, if seen parallel to a diode or bridge in a radio device has an other purpose. It is to short the HF to ground, otherwise you modulate your HF signals with the mains ferquency, because the device is periodically less or more connected to ground. Especially on transmitters power supply, but also on receivers.
Georg Beckmann
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Dear Omer,
don't apply such caps. They would in contrary slow down and expose the diodes to an additionally stored charge which then would load the diodes. To suppress RF interference by harmonics blocking the +B and /or across the secondaries may be more advisable. Since such phenomena depend from many circumstances (grounding / wiring) an experimental solution ist often the better way.
If You would feel safer, spend a few cent more and buy power Schottky or Avalanche diodes. They are fast switching.
Dont worry about the poor little vibrator contacts. They have anyway to deal with changing reactive load conditions, where current and voltage are not in phase. That means certain arcing is practically unavoidable.
By the way: To my understanding the 1N400x series diodes are neither designed for nor limited to 60 Hz sine wave rectification. They are found in multiple applications e.g. in TV sets. Of course not in high frequency circuits.
Anyway: Good luck!
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wiring diagram ?
as a non-expert regarding that area I would appreciate very much the provision of one or two simple wiring diagrams in order to improve the general understanding of your discussion. This would also help our beginners to perform follow up.
Best regards
Rolf
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(1)---[shell]
Parts referenced to http://www.mouser.com
Resistor, 2 each, 3 watt 220 Ohm
PN: 594-AC03W220R0J
data sheet: http://www.vishay.com/docs/28730/acseries.pdf
Diode, 2 each, IKV 1 Amp high speed. UF4007
PN: 512-UF4007
data sheet: http://www.fairchildsemi.com/ds/UF/UF4007.pdf
Pins (3) and (5) are the anode connections.
Pin (8) is the common cathode connection.
Pin (1) should go to the metal shell on the 0Z4 and 0Z4A versions.
At 110 mA, a 24 V drop is 2.64 watts. Assuming a 50% duty cycle, this gives better than 100% margin on the resistor power ratings.
Jeff
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