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Old 18th May 2002, 11:35 PM   #1
PassFan is offline PassFan  United States
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Default Magnavox 15wp-p

I built the Magnavox 15 watt paraphase circuit at Gabevees site using a hammond 1608 OPT. The transformer is possibly undersized however, the input sensitivity is 1.7 volts and I am driving it through a passive preamp right off my dvd so I'm no where near saturation. I was running it at 8 ohms with NFB driving a pair of 6 ohm TLs. I got a hair that needed plucking so I opened it up and rewired it for 4 ohms output and left the NFB on the 8 ohm tap. Well, it works and seems to have more detail as well.

Could this setup with the feedback on a different tap damage anything?

I have a different set of OPTs coming that are hammond 1650F. The 1650 has a 7600 ct and the 1608 has a 8000ct.

Is the plate to plate difference between the two going to make much of a difference with a 6bq5 output tube? Will the 1650 work?

The larger transformer will give me some room before saturation I'm sure and the website didn't get specific about OPTs. I found out from gabe after I built that he doesn't use 1608s.

Any help would be appreciated. Thanks
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Old 20th May 2002, 03:03 PM   #2
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About the NFB only. Typically for a 4,8,16 ohm tapped OPT the NFB is run off the 16 ohm tap no matter which tap you have your drivers set up to. And I am not sure but it could be that running a 6 ohm load on a 4 ohm tap will bring you closer to saturation faster than off the 8. As far as size goes it could be that your bandwidth is affected as much as power handling. Speaking off the cuff here since I don't know the specs.
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Old 20th May 2002, 04:19 PM   #3
PassFan is offline PassFan  United States
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Thanks for the response Thatch. The power output seems to be affected by the switch but the detail and soundstage improved. Looking at Hammonds hookup diagrams it appears that to utilize a 16 ohm tap a different wiring is required. I'm not sure if the four or 8 ohm tap would be available with this connection. It would appear that my setup will cause no adverse effects. I have seen some Magnaquest transformers around the same CT listed for use with a p-p 6bq5 output so I assume (uhoh) the larger hammond will work. The 1608 is 8000CT and the new one is 7600CT with a difference of +15 watts. Since I don't understand all the math involved I'm at the mercy of my ignorance. I don't want to ask Gabe because I feel it would be infringing on something else he might have in the works. One has to be prudent sometimes and not impose too much on those who go out of their way to help us out. Thanks
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