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Old 6th January 2010, 05:13 AM   #1
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Default Marantz 8b power transformer

I have what seems a simple question that my research has not found an answer to. Does anyone know what the 8b power transformer high voltage tap voltage and amperage is before rectification?
Thanks for any help you may provide.
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Old 6th January 2010, 11:16 AM   #2
chrish is online now chrish  Australia
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If you know the voltage you need after rectification, it is pretty easy to work out. The rectified voltage will be 1.414 times the AC voltage, less the voltage drop across the rectifier for a capacitor input supply. For a choke input it is about 0.9 times Les the rectifier drop.
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Old 6th January 2010, 12:34 PM   #3
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The 8b schematic shows 447v after the rectifier but before the choke input filter. So that figures to be about 316vac output from the transformer. I've seen this figure before but it doesn't match up to examples I've found. For instance the Kobayashi clone used 175v out of the transformer to get 460vdc. Also, what happens with the amperage? I need @300ma out of the supply. I know amperage decreases as voltage increases but by how much? Thanks, Kevin
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Old 6th January 2010, 02:27 PM   #4
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It's a voltage doubler circuit. Transformer is around 170V, 1.2A (about three times the DC current). I could come closer if I knew the exact voltage, load current and choke resistance.
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Old 7th January 2010, 12:56 AM   #5
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Thanks very much Tom. That seems to jive with the article explaining Kobayashi's 8b clone. Would you happen to know if there is a useable substitute transformer? I could have one custom wound, but I don't have that kind of money. I have a transformer for the bias supply and the heaters. I was thinking of a Hammond toroidal for just the high voltage supply. This might end up with more voltage than I would need.
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Old 7th January 2010, 01:22 AM   #6
chrish is online now chrish  Australia
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Edcor are very reasonably priced. They charge a one off $40 design fee. Even with this fee, it would probably be cheaper than an equivalent Hammond (if they had one with your required specification)
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Old 7th January 2010, 02:24 AM   #7
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Voltage doublers were pretty much the only game in town, when Marantz designed the 8B, if SS rectified B+ was to be used. He did not have access to the high PIV parts we have. You can build a highly suitable FWCT or FW Bridge B+ supply at very reasonable cost around the AnTek AN-2T350. $35 buys that trafo.
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Old 7th January 2010, 03:14 AM   #8
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Thanks everyone. If I would have found EDCOR sooner I would have only had to buy one transformer. I mistakenly bought a Hammond off EBAY that was right except for the amperage. But that Hammond with the Antek will give me a really strong power supply. Thanks again!
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Old 8th January 2010, 03:43 AM   #9
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Oh, by the way, any suggestions for caps and diodes? And do I need a choke with this type rectifier?
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Old 9th January 2010, 05:08 PM   #10
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I ordered the the antek. It will fit right next to the Hammond as the Hhammond is very small. Does anyone have suggestions for brands of filter caps and diodes. I've looked around and there are a multitude of types and manufacturerers. (sp?)

Also, I have seen bridge rectifiers using a single capacitor, a capacitor and a choke, and a capacitor then a choke followed by another capacitor. It seems the last might be the quietest? Again, thanks for any help you might be able to give. I bought the steel for the chassis today and want to geet started!
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