The GZ34 isn’t a very talked about tube, but it is one of the most common rectifier tubes found in audio, especially in guitar amps. Rectifier tubes were some of. Page 1. Page 2. Page 3. Page 4. Page 5. GZ34 page sheet date. 1. 1. 2. 2. 3. 3. 4. 4. 5. FP. GZ Netzröhre für GW-Heizung indirekt geheizt. Parallelspeisung. DC-AC- Heating indirectly heated connected in parallel. TELEFUNKEN. Zweiweg-.
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Bridge Rectifier A bridge rectifier is used to rectify AC from a transformer with a single winding i.
At any one time, two diodes conduct while the other two are switched off. Notice that all the diodes ‘point’ towards the positive output. You can either build a bridge rectifier from individual diodes or buy a single package. High-current bridge rectifier packages often have a hole in the middle so you can bolt them to the chassis.
GZ34 @ The Valve Museum
The first capacitor in the power supply -the reservoir capacitor- will be charged up to the peak value of the AC transformer voltage see the smoothing page. Under light loading, the DC output voltage will be equal to: What’s more, the AC transformer voltage Vrms will also sag as the load current increases.
Only when loaded to it’s full fz34 does the AC transformer voltage fall to its advertised value. For example, if you buy a transformer rated for “Vac mA” then you can expect it to produce anywhere from V to Vac with light loading.
After rectification this will produce a DC voltage somewhere between: When the transformer bz34 fully loaded to its mA rating the AC voltage will fall datasheft the nominal value of Vrms. The DC voltage will therefore fall to: However, on a low voltage supply for DC heaters, say the diode datashet represents a significant loss and should be considered.
Don’t forget about adding fuses! Required Diode Ratings The diodes in a bridge rectifier need to have an average forward current rating that exceeds the maximum DC load current in your circuit.
The popular 1N is rated for 1 amp, which is far more than the maximum HT current in any guitar amp.
GZ34 Datasheet PDF –
However, something like a DC heater supply would probably need beefier diodes. Diodes also have peak and surge current ratings, but you don’t have to worry about these as they are always well in excess of what you need, provided the average current dwtasheet is adequate for the job.
The peak AC voltage is equal to 1. The popular 1N is rated for V. Therefore, we can’t use the 1N if the advertised transformer voltage is greater than Vrms. Fortunately, you don’t see such high voltages in guitar amps. The story is different with gz43 two-phase rectifier see later. Hybrid Bridge Rectifier Ordinary full-wave valve rectifiers cannot be set up as a bridge since they have a single shared cathode.
However, you can easily use a pair of silicon diodes to complete the bridge. Under light loading the DC output voltage will again be equal to: As a rough approximation, at full load the DC output voltage will normally be between 1 and 1.
You can read about more accurate voltage prediction here. Valve rectifiers can’t handle the high current levels that silicon diodes can. For example, the GZ34 is rated for only mA average. Valve rectifiers sometimes also need current-limiting resistance to protect them see shortly from excessive ripple and surge currents.
In the hybrid bridge hybridge? Two-Phase Rectifier The two-phase rectifier is used with a transformer that has a centre tap. Really it is a pair of half-wave rectifiers, each feeding the same load. At datzsheet time, one diode is on and the other is off. Beginners sometimes call the two-phase rectifier a ‘full-wave rectifier’. A bridge rectifier is also a type of full-wave rectifier. Vintage power supplies used two-phase rectifiers because it dataeheet only two diodes which could be in the same bottle.
This also means the rectifier valve needs only datawheet heater supply. The vast majority of valve guitar amps still use two-phase rectifiers even when they use solid-state diodes.
This is partly historical and partly because a centre-tapped transformer makes it easy to generate a negative bias supply.
Two full-wave rectifiers orientated in opposte directions creates a bipolar supply positive and negative DC. This is common in solid-state amplifiers. Superficially this looks like a bridge rectifier and you can indeed use a bridge rectifier diode packagebut it is best viewed as a pair of two-phase rectifiers. The same basic principles hold for the two-phase as for the bridge rectifier. Required Diode Ratings The diodes in a two-phase rectifier need to have an average forward current rating that comfortably exceeds the maximum DC load current in your circuit.
This should be no problem with modern silicon diodes. Again, you don’t have to worry about peak and surge current ratings, provided the average current rating is adequate for the job. The diodes must also have a Reverse Repetative Maximum Vrrm rating that exceeds the peak-to-peak AC voltage measured from one end to the cente taptwice the value needed for a bridge rectifier.
This is equal to 2. A 1N is rated for V. In other words, we shoudln’t use the 1N with anything more than a V transformer.
What if the transformer voltage is higher than this? The best option is to buy diodes with higher voltage ratings, but they’re not nearly as common as the 1N A classic alternative is to use two or more diode in series, so they share the burden.
However, we must ensure that the voltage is shared at least roughly equally. This can be done by adding a 10nF to nF capacitor in parallel with each diode.
High-value resistors could alternatively be used, but it is a lot easier to find 1kV-rated ceramic capacitors than 1kV-rated resistors.
Valve Rectifiers Ordinary valve rectifiers contain two diodes which share the same cathode and heaterin one bottle. Valve rectifier data sheets usually state the maximum RMS transformer voltage that the valve can withstand in an ordinary two-phase rectifier circuit, rather than quoting limits in peak values like modern dataseet sheets. The GZ34 data sheet quotes Vrms although personally I wouldn’t trust a modern production bottle to handle this.
The data sheet will also quote the maximum average DC current that the valve can handle. Satasheet the Satasheet this is mA for a capacitor-input rectifier with transformer voltages up to V, but the limit is reduced for higher transformer voltages.
The limit is higher for gz334 circuits, but guitar dqtasheet don’t use those, so you don’t have to worry about it. Most valve rectifiers also need their own, dedicated heater supply.
The EZ81 is a notable exception.
GE 5AR4 Datasheet
In addition to the maximum AC voltage and DC current ratings, valve rectifiers have two other ratings that must be observed: These two limits are interelated and serve to keep the peak ripple current below a certain bz34 level. The bigger the reservoir capacitance, the more limiting resistance you need. The GZ34 data sheet quotes datashet maximum capacitance of 60uF, although you can, in theory, exceed this if you increase the limiting resistance proportionately.
However, this incurs extra voltage loss and wasted heat which is why the manufacturer assumes no one ggz34 want to datadheet it. The total limiting resistance per anode in the actual circuit is the combnation of transformer resistance, datasheer any resistance we add ourselves: Rpri is the DC resistance of the transformer’s primary winding; Rsec is the DC resistance of one half of the transformer’s datashert winding, i.
The data sheet will present table or graphs showing the minimum limiting resistance needed for a given application. If the datasbeet alone doesn’t have enough resistance to meet this requirement then you need to make up the deficit by adding resistors in series with each anode.
These resistors need to have a power rating that comfortably exceeds: Valve rectifiers have realtviely high internal resistance. This causes a significant loss of voltage which increases with load current, leading to power supply voltage ‘sag’ during loud passages.
The data sheet will usually contain various graphs and tables of recommended operating conditions, some showing how much the voltage will sag with different load currents, so it should be fairly easy to extrapolate this information into your own design.
As a rough rule of thumb, at full load a valve rectifier will produce a DC voltage that is between 1 and 1. Vaccum rectifiers must not be ‘hot switched’, i.
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