You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

A zener works by stealing current from the load that's being regulated. To make a zener regulate properly, either choose a zener with a lower circuit voltage than the 100 Volts or so the tube uses now, or reduce the resistance of the series pair R319+R320. They add up to 44K. Since they drop around 300 Volts, the current through the tube V302B is just under 7 mA. If we double the resistor's current to 14 mA, the zener can take half of it, V302B the other half. A 100-Volt zener will have to dump 100 times .007, or around 3/4 of a Watt. Just shorting across one of the two 22k resistors would do the trick. But using 22k for R319+320 means that single resistor will dump almost four and a half Watts. This calls for a 10 or 15-Watt dropping resistor to take their place and keep the temperature in reason. The zener should be a 5-Watt part. And no, you should never dump 3/4 of a Watt into a 1-Watt zener. That's a peak 1-Watt rating. Average rating in the real world is half to one-quarter of a Watt, depending on the surrounding temperature. A 5-Watt part will be dumping under 20% of that 5 Watt rating and won't overheat. And the "drifts when I key on sideband" problem will NOT be influenced in a big way. But the B+ will be regulated.

73

<blockquote data-quote="nomadradio" data-source="post: 812907" data-attributes="member: 22">A zener works by stealing current from the load that&#039;s being regulated. To make a zener regulate properly, either choose a zener with a lower circuit voltage than the 100 Volts or so the tube uses now, or reduce the resistance of the series pair R319+R320. They add up to 44K. Since they drop around 300 Volts, the current through the tube V302B is just under 7 mA. If we double the resistor&#039;s current to 14 mA, the zener can take half of it, V302B the other half. A 100-Volt zener will have to dump 100 times .007, or around 3/4 of a Watt. Just shorting across one of the two 22k resistors would do the trick. But using 22k for R319+320 means that single resistor will dump almost four and a half Watts. This calls for a 10 or 15-Watt dropping resistor to take their place and keep the temperature in reason. The zener should be a 5-Watt part. And no, you should never dump 3/4 of a Watt into a 1-Watt zener. That&#039;s a peak 1-Watt rating. Average rating in the real world is half to one-quarter of a Watt, depending on the surrounding temperature. A 5-Watt part will be dumping under 20% of that 5 Watt rating and won&#039;t overheat. And the &quot;drifts when I key on sideband&quot; problem will NOT be influenced in a big way. But the B+ will be regulated.73</blockquote>

[QUOTE="nomadradio, post: 812907, member: 22"] A zener works by stealing current from the load that's being regulated. To make a zener regulate properly, either choose a zener with a lower circuit voltage than the 100 Volts or so the tube uses now, or reduce the resistance of the series pair R319+R320. They add up to 44K. Since they drop around 300 Volts, the current through the tube V302B is just under 7 mA. If we double the resistor's current to 14 mA, the zener can take half of it, V302B the other half. A 100-Volt zener will have to dump 100 times .007, or around 3/4 of a Watt. Just shorting across one of the two 22k resistors would do the trick. But using 22k for R319+320 means that single resistor will dump almost four and a half Watts. This calls for a 10 or 15-Watt dropping resistor to take their place and keep the temperature in reason. The zener should be a 5-Watt part. And no, you should never dump 3/4 of a Watt into a 1-Watt zener. That's a peak 1-Watt rating. Average rating in the real world is half to one-quarter of a Watt, depending on the surrounding temperature. A 5-Watt part will be dumping under 20% of that 5 Watt rating and won't overheat. And the "drifts when I key on sideband" problem will NOT be influenced in a big way. But the B+ will be regulated. 73 [/QUOTE]

Top Bottom