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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Cheap Toroid OPTs posted by olen on April 7, 2002 at 01:14:06:
...tried both schemes already . Parafeed used mosfet CCS loading instead of a choke , much cheaper ! OPtx was 240V:7v 30VA mains toroid unit , measured nearly 200H . Currently working on a fully differential push pull amp using a 115/115:6/6 50VA mains toroid . It measured 150H , larger VA types are not quite so good . For instance a 100VA 115/115:9/9 unit only measured 80H so there is a major tradeoff with primary inductance/power handling . Also I'm in the UK , we use 50Hz instead of 60Hz , mains , therefore the core sizes possibly will be bigger , so you may not be able to duplicate the results using US spec'd tx's . If anyone is considering using mains toroids push pull , I can strongly recommend using a zero balance meter and variable bias . Toroids don't like DC , so this should help to balance anode currents . Others have tried them parafeed too , in this application they seem to work extremely well . What applies to both parafeed and push pull : use low Ra valves (parallel 12b4a / pl504 / 7236 / 5998) . PL504 triode strapped seems to be the best tradeoff in terms of linearity and drive (Ra 600r , -40V , 250V , Pdiss=17W) , dirt cheap too , my Mullards cost me £1 each new . Avoid 6080 , the bias requirements are too severe . As I stated above , there are tradeoffs associated with different VA ratings and the turns ratio , best to use the 6/6 units as a starting point in my opinion .
...FB
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Follow Ups
- Re: Cheap Toroid OPTs - fatbottle 04/7/0203:13:18 04/7/02 (3)
- Re: Cheap Toroid OPTs - Scholl 09:23:03 04/8/02 (1)
- Re: Cheap Toroid OPTs - fatbottle 10:21:32 04/8/02 (0)
- Re: Cheap Toroid OPTs - Scholl 09:22:48 04/8/02 (0)
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