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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="BarryD" data-source="post: 195151" data-attributes="member: 13633"><p>I keep having to stop myself from typing "Hi handsome...", my wife may see this forum!</p><p>Those 5W droppers have come down in value from 5k5 to their current 3470 ohms. So total current is now 20mA, the preamp itself draws 10.4mA, so around 10 going through the glow tubes. Much heat was generated in the process, hence now 5W. OD3 is rated 5-30mA, but I have found that operating close to the bottom end gave poor regulation - see previous posts on mains and resulting troubles! Also discovered that the voltage vs current characterisic is not a straght line, these things are not zener diodes!</p><p>The DC CF is fussy about power supply. If the preamp is able to modulate the HT to any degree, there is a marked deterioration, hence all the Glow Tubes and chokes and caps. My first CF was RC coupled, and much less fussy, just had a standard RC network for a filter, didn't even have a choke. That is likely because the two stages work out of phase with each other, whereas with the DC coupling they are in phase, so "gang up" on the power supply.</p><p>The long and the short of it is that you are right, best to operate the glow tubes somewhere in the mid to upper portion of their range. Curiously, I have had about 6 different values in for that dropper, and the thing didn't sound different. Though to be fair, I was preoccupied with other things - not spending hours each time listening to it!</p></blockquote><p></p>
[QUOTE="BarryD, post: 195151, member: 13633"] I keep having to stop myself from typing "Hi handsome...", my wife may see this forum! Those 5W droppers have come down in value from 5k5 to their current 3470 ohms. So total current is now 20mA, the preamp itself draws 10.4mA, so around 10 going through the glow tubes. Much heat was generated in the process, hence now 5W. OD3 is rated 5-30mA, but I have found that operating close to the bottom end gave poor regulation - see previous posts on mains and resulting troubles! Also discovered that the voltage vs current characterisic is not a straght line, these things are not zener diodes! The DC CF is fussy about power supply. If the preamp is able to modulate the HT to any degree, there is a marked deterioration, hence all the Glow Tubes and chokes and caps. My first CF was RC coupled, and much less fussy, just had a standard RC network for a filter, didn't even have a choke. That is likely because the two stages work out of phase with each other, whereas with the DC coupling they are in phase, so "gang up" on the power supply. The long and the short of it is that you are right, best to operate the glow tubes somewhere in the mid to upper portion of their range. Curiously, I have had about 6 different values in for that dropper, and the thing didn't sound different. Though to be fair, I was preoccupied with other things - not spending hours each time listening to 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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