Apologies to Alex Kitic- RH84 Three Channel?

[jsax420]

First, let me say that I have successfully built an RH84 using motor run caps and Transcendar OPT’s, and it is a most wonderful amp. Now I’ve picked up a small Zenith SE el84 console and I’m interested in changing the circuit into another RH84, but the Zenith is set up with three OPT’s, two small ones for left/right and a third, larger one for a central ten inch bass speaker. I’ve 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 don’t know for sure if it will work. (Again, my apologies Mr. Kitic, I understand you don’t care for modifications to your design, and yet, curiosity compels me…)
Would anyone with actual knowledge care to comment on my effort? I don’t have the Zenith schematic, and I haven’t measured the impedance of the OPT’s, so I’m kinda just thinking out loud right now. I can always buy a couple of small Edcors and change to two speakers, but it’s all set up for the three, and the connections for the third look to be straightforward… I know that doesn’t mean it will work though. All comments are welcome, even if it’s just that I’m wasting my time. Thanks!

[planet10]

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

[planet10]

Here is the map i traced from a similar Motorola amp...

dave

[pjanda1]

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.

pj
www.wildburroaudio.com

[jsax420]

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.