Apologies to Alex Kitic- RH84 Three Channel? - diyAudio
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Old 21st May 2009, 03:33 PM   #1
jsax420 is offline jsax420  United States
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Question Apologies to Alex Kitic- RH84 Three Channel?

First, let me say that I have successfully built an RH84 using motor run caps and Transcendar OPTís, and it is a most wonderful amp. Now Iíve picked up a small Zenith SE el84 console and Iím interested in changing the circuit into another RH84, but the Zenith is set up with three OPTís, two small ones for left/right and a third, larger one for a central ten inch bass speaker. Iíve traced the RH84 schematic with two signal portions for left/right, and tried to graft in the third OPT in the way it was connected originally, but I donít know for sure if it will work. (Again, my apologies Mr. Kitic, I understand you donít care for modifications to your design, and yet, curiosity compels meÖ)
Would anyone with actual knowledge care to comment on my effort? I donít have the Zenith schematic, and I havenít measured the impedance of the OPTís, so Iím kinda just thinking out loud right now. I can always buy a couple of small Edcors and change to two speakers, but itís all set up for the three, and the connections for the third look to be straightforwardÖ I know that doesnít mean it will work though. All comments are welcome, even if itís just that Iím wasting my time. Thanks!
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Old 21st May 2009, 05:00 PM   #2
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I've traced a couple of these... i don't know if you want the separate B+ feed to the SE OPTs. And the bracketed caps will block low frequency signal to the bass driver.

We need some guys that really know in the thread.

This was a fairly common way of adding a common woofer. The PP OPT acts as both an OPT and as a filter choke

The more upmarket ones had a 3rd amplifier for the bass.

dave
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Old 21st May 2009, 05:17 PM   #3
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Here is the map i traced from a similar Motorola amp...

dave
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Old 21st May 2009, 07:14 PM   #4
pjanda1 is offline pjanda1  United States
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I've occasionally pondered it, and it surprises me that diy'ers aren't currently taking this approach: two widebands a single woofer. It seems to have a great deal going for it. I've got an old phonola sort of thing with a terrible (and unsafe power supply less) amp that uses two little alnico satellite drivers and a bigger woofer in the big box. I know plenty of consoles have done it. It seems like a great way to do either a small main system, or especially a desktop system. Maybe something with the tiny Fostex's and a highish efficiency woofer? The world is full of ideal donor units for drivers and iron as well, but I can't remember seeing anyone build such a system. I hope folks chime in.

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Old 21st May 2009, 07:52 PM   #5
jsax420 is offline jsax420  United States
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Thanks for the encouragement gentlemen! I think I will try it and see what happens, at least now I'm pretty confident it won't burst into flames... I sure hope it works, the console is small, but is in pretty nice shape, and it fits perfectly in my shop room.
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