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Magnavox 185BB Build/Questions
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Author:  ubuntu9786 [ 28 Feb 2019, 13:47 ]
Post subject:  Magnavox 185BB Build/Questions

Hello DIYaudioprojects!

I am a long time reader here but first time poster. After seeing all the cool projects done here and having been interested in audio pretty much forever, I was inspired to convert a Magnavox 185BB console amplifier to a stand-alone unit. I am a little confused however on what is going on and I was hoping someone here could help me out, as I have seen others post their builds of these here.

I used the original inputs to figure out where the signal left the phonostage section, I soldered two small jumper wires from the center of the RCA jack to pins 2 and 7 of the 3rd 12AX7 tube. This then allowed me to remove the tube, because this is being essentially skipped, and the sound changed from very quiet and bassy (as expected from a phonostage) and sounded louder, not distorted, and normal.

I then went, a day later, and added wires from those same pins to the back to new rca jacks and now get almost no sound, and it is only on one channel. So I was thinking, wait doesn't the signal go into the grid and come out of the plates amplified? So I moved the inputs to pins 1 and 6, which are the two plates of that first 12AX7, which makes more sense on skipping that stage of the schematic, as that's where signal leaves that first tube and moves on. But now I have almost no volume at all, its distorted, and I have only one channel. The other strange thing is that the balance, which previously when one channel was working would still work, just go from the functioning side to silence, now does nothing at all and the very quiet volume stays constant on one side. I still have the original small jumper wires I put in from the old RCA jacks to the grids, and those also have the same problem if I use those as the inputs.

I am also a little unsure if the place I have connected the speaker outputs is the best way. I am now confused pretty much on what my next steps are. Any advice would be helpful! Below are two pictures which are the schematic. I for some reason cannot seem to make the photos of the amp under 500KiB, but I can post a link to imgur if that is allowed.

I will continue to update this thread as I move along! Thank you for your time.

Author:  ILoveHiFi [ 01 Mar 2019, 01:47 ]
Post subject:  Re: Magnavox 185BB Build/Questions

Seems like you probally connected something by accident in wrong place etc.

Should work if you bypass and directly input signal to grid

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