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Audio and Video Talk
Valves / Vacuum Tubes
How to design a Power Transformer for a Push-pull tube amplifier?
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<blockquote data-quote="handsome" data-source="post: 195370" data-attributes="member: 772"><p>Barry: when it comes to resistors in valve amps there are three simple rules: over-rate, over-rate, over-rate. Most modern film resistors cannot handle more than 300V so it always pays to check the specs. Carbon comps can handle very high transient overloads but they drift terribly with temperature and applied voltage plus they are noisy as heck. Wirewounds are usually the best choice, certainly on technical grounds: higher voltage ratings and very low noise. Another good trick is to use wirewound resistors in the RC filters in PSUs. their minute amount of inductance in combination with a small film capacitor make RF filters whilst the resistance plus large probably electrolytic capacitor does the standard hum filtering job. </p><p></p><p>Mars: There is a very good tutorial on the web somewhere on using PSUD. Essentially one should aim to have a very smooth 'line' from initial zero to quiescent voltage. if there are any spikes or peaks along the line this indicates ringing. if you fiddle with the value of the resistor in your design you will be able to see it. The trade off of course is supply impedance - we would like a very low impedance of course - versus ringing. the ringing is ultimately a combination of transformer resistance and inductance plus the value of the first capacitor. I dont worry about single transients exceeding the tube ratings as they usually just occur once at start up and the tubes can (should?) handle it.</p></blockquote><p></p>
[QUOTE="handsome, post: 195370, member: 772"] Barry: when it comes to resistors in valve amps there are three simple rules: over-rate, over-rate, over-rate. Most modern film resistors cannot handle more than 300V so it always pays to check the specs. Carbon comps can handle very high transient overloads but they drift terribly with temperature and applied voltage plus they are noisy as heck. Wirewounds are usually the best choice, certainly on technical grounds: higher voltage ratings and very low noise. Another good trick is to use wirewound resistors in the RC filters in PSUs. their minute amount of inductance in combination with a small film capacitor make RF filters whilst the resistance plus large probably electrolytic capacitor does the standard hum filtering job. Mars: There is a very good tutorial on the web somewhere on using PSUD. Essentially one should aim to have a very smooth 'line' from initial zero to quiescent voltage. if there are any spikes or peaks along the line this indicates ringing. if you fiddle with the value of the resistor in your design you will be able to see it. The trade off of course is supply impedance - we would like a very low impedance of course - versus ringing. the ringing is ultimately a combination of transformer resistance and inductance plus the value of the first capacitor. I dont worry about single transients exceeding the tube ratings as they usually just occur once at start up and the tubes can (should?) handle it. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
How to design a Power Transformer for a Push-pull tube amplifier?
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