Glass Ware Janus Operation & User’s Manual

Text of Glass Ware Janus User Guide:

• GlassWare Audio Design 6 Furthermore, toroids easily saturate in the presence of a sustained DC current through a winding. Because the magnetic circuit is so tight in a toroid, any DC current flow can magnetize the toroidal core, thereby robbing the transformer of its effectivenes s. In other words, toroids are perfect, except that they aren’t. My recommendation is to only us

• Glass Ware Janus, GlassWare Audio Design 15 For example if the mu of the triode is 35, then the 1 mA current decrease would only result in a 0.0011 volt, as the output impedance of the regulator is about 11 ohms: Zo = (Ra||rp) /Gain but as Gain = µRa / (Ra + rp) and Ra||rp = Ra•rp / (Ra + rp) thus Zo = [Ra•rp / (Ra + rp)] / [µRa / (Ra + rp)] Zo = rp / µ or Zo = 1 / Gm. In this case Zo = 400 / 35. So we see that what really matters is Gm (transconductance), as the greater the Gm, the lower the output i mpedance. One triode might have a mu of 10 and an rp of

• Glass Ware Janus, GlassWare Audio Design 5 Fortunately, Eddy currents are proportional to the square of the core thickness. Therefore, if the core is made thin enough, we can ignore the Eddy currents. This what the laminations do, as they are very thin and electrically insulated from each other by wax or shellac. Large and heavy, typical EI-core transformers do not seem suited to modern sleek and slender enclosures. Additionally, they present relatively higher winding DC resistances and, as a result, deliver a more load-dependent secondary voltage.

• Glass Ware Janus, GlassWare Audio Design 11 Rectifier Circuits Tube equipment was born to run on DC and everywhere it is chained to AC wall sockets . In other words, all power supplies that plug into wall sockets, must convert AC voltage to DC voltage. This conversion requires rectifiers and capacitors; and there are several ways that the rectifiers can be configured. Full-Wave Center-Tap This is the classic tube amplifier power supply configuration. It uses only half of secondary winding at a time and requires a center - tapped winding and t

• Glass Ware Janus, GlassWare Audio Design 3 Maximum and Minimum Wall Voltages A reasonable guess on the absolute upper limit of sustained higher line voltage would be around 127vac in the USA , as the power company— which could be held liable for damaging your microwave oven, if the voltage became too hot—is very quick to prevent an over- voltage. The lower limit is usually set to around 108vac here in the USA . You can, however, choose to design around an even wider variation, say 100-130vac. RFI The art and science of stripping away RFI can fill a large book. Radio frequency interference comes from more than just radio stations. Light dimmers, computers, c

• Glass Ware Janus, GlassWare Audio Design Janus PCB [Rev. A] The Janus circuit board makes life quite a bit easier for the tube fancier. On this small 5 by 6 inch, extra thick (0.094), 2oz-copper traces, USA-made PCB resides both a low - voltage and a high -voltage regulator, with each regulator finding its own raw power supply, including the rectifiers and power-supply reservoir capacitors. In other words, except for the power transformers, the Janus PCB holds all that is needed to make a superb tube-circuit power supply. The low-voltage regulator is meant to supply the tube h

• GlassWare Audio Design 10 So what good are photo-flash capacitors? These capacitors are quite suitable for low - ripple power supply use; say for the first stage of an amplifier’s RC filter , after being fed by a high-ohmage voltage-dropping resistor. Another use is as the output coup ling capacitor in an OTL amplifier. In fact, one OTL manufacturer found that they

• Glass Ware Janus, GlassWare Audio Design 13 Voltage Regulators A voltage regulator is an electronic circuit that strives to maintain a constant output voltage— in spite of variations in either the wall voltage or the current drawn by the load. A voltage regulator does with complex circuitry what a ca r battery does by brute force: it maintains a steady and accurate output voltage over a large range of load current. Regulators fall into two groups: switching and linear. In terms of sales, flexibility, conversion efficiency, and weight to power output, t he

• Glass Ware Janus, GlassWare Audio Design 21 Heater Power Supply & Regulator The Janus PCB also holds a low-voltage power supply and voltage regulator. Below is the heater power supply schematic used on the Janus PCB. As can be seen, the power supply can accept either full-wave bridge rectifier circuit or a full- wave voltage doubler rectifier configuration. When used as a full- wave bridge rectifier circuit, the two power supply filtering capacitors are oriented with their positive leads pointing to the top of the PCB, where the heatsink sits; configu red as a voltage doubler, these capacitors are rotated 90 degrees clockwise, s

• Glass Ware Janus, GlassWare Audio Design 19 33µF - 450V 4.7µF - 400V 220µF - 160V 0.33µF 160V 1N4007 or better 100 1W 300 200k 1.5k 3W 10k 3W 300k 1W 100k 1W 5AR4 or 5R4 or 5Y3 7247 or 12DW7 or ECC832 5V@2A 400Vac to 550Vac (requires center-tap)* 200Vac to 275Vac (requires using D8 & D9)* *Current rating depends on load. Usually, 50mA to 100mA is adequate. The limiting factors are the 5W 1500-ohm series resistor, the 4.7µF/400V film capacitors, and leftmost triode’s plate dissipation. The power transformer’s selection is somewhat critical, as too high a primary voltage will create too high a B+ voltage. Unfortunately, most high-voltage power t

• Glass Ware Janus, GlassWare Audio Design 18 Note the use of a tube rectifier, either a 5AR4, 5R4, or 5Y3. S ince the Janus regulator uses solely tubes, why not go all tube. Or, if you choose, solid- state rectifiers can be used exclusively . Also note the lack of DC voltages in the schematic. This impl ementation of the Janus regulator was designed to deliver between +250V to +300V worth of B+ voltage. The Janus regulator is not, however, a DC voltage regulator, as it cannot maintain a fixed B+ voltage; instead, it works to el

• Glass Ware Janus, GlassWare Audio Design 23 Modifications & Part Upgrades Tubes The tube rectifier (V1) and the dissimilar twin-triode regulator tube (V2) are new production stock. Several Janus regulator users have used long-out-of- production NOS tube replacements and gotten excellent results. For example, old 5Y3 rectifiers and 12DW7/7247/ECC832 tubes are still available at somewhat reasonable prices. The rectifier offers the widest choice of suitable replacements, such as the 5AR4/GZ34, 5R4GB (avoid the version with the large bulbous base), and even the WE274. For the truly advanced practitioner, a different regulator tube (V2) can be used, such as the 12BH7 or ECC99.

• Glass Ware Janus, GlassWare Audio Design 14 The triode's current can be varied by varying grid-to- cathode voltage, which is why the triode is called a "valve" in England. The same grid-to- cathode voltage creates a soft voltage reference, as the triode's plate will buck or fight any change in plate v oltage. This occurs because a triode, unlike a pentode or a transistor or MOSFET, exhibits plate resistance (rp). For example, a 4k resistor attached to a power supply of 400 volts will experience a current flow of 100 mA. Moving the power supply voltage u p and down will increase and decrease the current flow through the resistor, as

• Glass Ware Janus, GlassWare Audio Design 17 Shunt Regulator The Janus shunt regulator made its first appearance in 2007, in the Tube CAD Journal . In a nutshell, the Janus shunt regulator uses both feedforward- and feedback- based shunt regulation to reject both the rectifier-induced power-supply noise and the signal - induced power- supply noise from its output. In the simplified circuit shown below, we see the rightmost triode doing the double duty of voltage dividing the raw power supply ripple by a fixed amount and by amplifying the error signal at the regulator's ou tput, and then passing the correction signal to the leftmost triode's grid, which then the leftmost

• Glass Ware Janus, GlassWare Audio Design 12 Full-Wave Voltage Doubler Although often shunned by tube fanciers, there is nothing wrong with this power supply configuration. The full- wave voltage doubler circuit doubles the voltage that a full- wave bridge rectifier circuit would provide, but with onl y half the output current capability. And t he ripple is at the same 100Hz or 120 Hz frequency as in the full-wave bridge rectifier circuit. R load In this circuit, the transformer core is not partially magnetized as it is in simple half - wave p

• Glass Ware Janus, GlassWare Audio Design 8 Electrolytic Capacitors This type of capacitor displays the poorest temperature stability, the most leakage, the most noise, and the shortest lifespan of any capacitor. NASA prohibits the use of electrolytics in space flight, because of high failure rate and their possible venting of noxious fluids and gases. The reason we put up with the electrolytic is because of its volumetric efficiency; we hunger for capacitance, lots of capacitance. A tube power amplifier’s power supply needs at least 50-µF and solid- state amplifier’s need closer to at least 10,000-�

• Glass Ware Janus, GlassWare Audio Design 2 Standard Power Supplies A “standard power supply” is one that is not regulated. A standard power supply can be simple or complex, unipolar or bipolar, low voltage or high voltage, low current or high current, vacuum tube rectified or solid state rectified, choke-free or choke-filled— the only disqualification is having a regulator. As most regulated supplies must also incorporate a standard power supply as their voltage source, an understanding of the standard power supply is primary to understanding voltage regulation. The Function of a Power Supply Obviously, a power supply’s purpose is to provide a

• GlassWare Audio Design 16 +310V +300V -20V -20V 0V R gm 1M 100 20mA 80mA 0V 0.1µf This surge in current will then combine with the 8 0mA drawn by the load and the existing idle current flowing through the tube, 20mA . When the added 10mA increase in current travels through the series resistor, whose value equals 1/0.01, or 100 ohms, the r esistor wi

• Glass Ware Janus, GlassWare Audio Design 22 Assembly & Testing Assembly Cleanliness is essential. Before soldering, be sure to clean both sides the PCB with 90% to 99% isopropyl alcohol. Do not use dull- looking solder; solder should shine. If it doesn’t, first clean away the outer oxidation with some steel wool or a copper scouring pad. If the resistor leads look in the least gray, clean away the oxidation with either steel wool or a wire sniper’s sharp edges. Admittedly, with new resistors and a fresh PCB, such metal dulling is rare; but if the par ts have sat in your closet for a year or two, then expect a good amount of oxidation to have dev

• Glass Ware Janus, USER GUIDE AUDIO DESIGN 10/19/2008 GlassWare Low- & High-Voltage Regulators Shunt Regulator Janus PCB Overview Introduction to Power Supplies Standard Power Supplies The Function of a Power Supply Wall Outlet Voltage Problems The Parts of a Power Supply Rectifiers Capacitors Types of Electrolytic Capacitors Capacitor Safety Rectifier Circuits Voltage Doubler Circuits Voltage Regulators Janus Shunt Regulator Schematic & Part Values Transformers & Rectifiers Heater Power Supply & Regulator Assembly and Testing Modifications & Part Upgrades Operation Janus PCB Dimensions Page

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