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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: 195297" data-attributes="member: 13633"><p>Someone else who has done almost exactly the same thing is Winders. He has 76's for preamp and CF, 2 X VR150 etc, he had a lot of input into my design, in fact without his assistance, hard to say where this would have ended up! I used stoppers on my first (RC coupled) preamp, 1K grid stopper, and 330R cathode stopper. So far haven't seen any signs of instability with any of my CF's. When I had that problem a couple of weeks ago, one of my first thoughts was that I might have made a relaxation oscillator out of the VR's + choke + cap, turned out not to be the case.</p><p> </p><p>Previous comment about the RC filter on my previous preamp - it wasn't the best, I just got away with it when it was RC coupled - when I rewired it as DC coupled, it was dreadful, five minutes with the scope showed bad modulation of the power supply. That alerted me to the fact that I had to regulate the HT, something which seems to be obvious to others (well - yourself and Winders anyway!).</p><p> </p><p>Interesting that you mention carbon composition resistors - I try to use them as much as possible. I have discovered that metal film resistors, even if very conservatively rated, don't like high voltage or heat. My Williamsons suffered from this to begin with, the values creep, but luckily upwards, so no harm was done, just the amp did not hold its setup. </p></blockquote><p></p>
[QUOTE="BarryD, post: 195297, member: 13633"] Someone else who has done almost exactly the same thing is Winders. He has 76's for preamp and CF, 2 X VR150 etc, he had a lot of input into my design, in fact without his assistance, hard to say where this would have ended up! I used stoppers on my first (RC coupled) preamp, 1K grid stopper, and 330R cathode stopper. So far haven't seen any signs of instability with any of my CF's. When I had that problem a couple of weeks ago, one of my first thoughts was that I might have made a relaxation oscillator out of the VR's + choke + cap, turned out not to be the case. Previous comment about the RC filter on my previous preamp - it wasn't the best, I just got away with it when it was RC coupled - when I rewired it as DC coupled, it was dreadful, five minutes with the scope showed bad modulation of the power supply. That alerted me to the fact that I had to regulate the HT, something which seems to be obvious to others (well - yourself and Winders anyway!). Interesting that you mention carbon composition resistors - I try to use them as much as possible. I have discovered that metal film resistors, even if very conservatively rated, don't like high voltage or heat. My Williamsons suffered from this to begin with, the values creep, but luckily upwards, so no harm was done, just the amp did not hold its setup. [/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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