Author Topic: FS Magnavox Serenade  (Read 305 times)

Bill

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Re: FS Magnavox Serenade
« Reply #15 on: September 21, 2018, 04:52:34 PM »
Chris,

I'm not sure what year it was, as I no longer have it.  It looks just like the one in the 1956 brochure in the downloads.  I still might have a photo of it, if I can find it I'll post it. 

Bill

ed from Baltimore

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Re: FS Magnavox Serenade
« Reply #16 on: October 18, 2018, 10:57:44 PM »
  I think there might be a single treble amp 6V6 that is hidden  by the larger 5U4 in this particular photo angle. I see the 6AT6 treble driver tube to the left next to the filter caps and in a photofact I had the photo angle showed the 6AT6 6V6  treble tubes lined up like that. 

ed from Baltimore

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Re: FS Magnavox Serenade
« Reply #17 on: October 18, 2018, 11:26:08 PM »
   I didn't know Magnavox ever used two output transformers with the same output tubs for bass and treble. I've seen bi-amp Magnavoxes with separate input crossover circuits sealed in a transformer-like metal can, but I think those had separate output tubes and transformers for bass and treble. Maybe in a late forties unit with 4 6L6s and one treble 6V6  .
    I've seen the schematic for an elaborate RCA chassis from the late thirties with the split bass and treble transformers going to the same output tubes. the tubes were either 6F6s or 6L6s and it had a separate tweeter  speaker.  A Philco circuit with 6L6s had an electrostatic tweeter coupled to the push-pull primary winding through some kind of RC circuit so that the output transformer only handled bass to the bass speaker. Some of the Magnavoxes with input transformers had no preamp tubes on the amp chassis at all, just power tubes and rectifier tubes. The radio chassis had a cathode follower driving the input transformer, I think, like a 6J5.
     the units with 4 6L6s for two 15 inch woofers and a separate 6V6 driving an efficient horn treble must have been able to play quite loud and they were probable always placed in a large room since if you could afford a big Magnavox you probably had a house with big rooms.

TC Chris

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Re: FS Magnavox Serenade
« Reply #18 on: October 19, 2018, 04:59:45 PM »
   I didn't know Magnavox ever used two output transformers with the same output tubs for bass and treble. I've seen bi-amp Magnavoxes with separate input crossover circuits sealed in a transformer-like metal can, but I think those had separate output tubes and transformers for bass and treble. Maybe in a late forties unit with 4 6L6s and one treble 6V6  .
   

Look at the AMP 149 schematic I posted in the downloads section--four 6V6s in P-P parallel; two output transformers connected in parallel to the same 4 tubes.  I think of it as "quasi-biamped."  I thinkit's kinda cool, because it probably would have sounded almost the same with one output transformer (the bass one is sizeable), but somehow the cost accountants let them use two instead.  It's interesting to see where they spent money and where they cheaped out.

Chris Campbell

Chris Campbell

ed from Baltimore

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Re: FS Magnavox Serenade
« Reply #19 on: October 20, 2018, 01:49:05 AM »
  You are so right, Chris !!! The amp 149 had the two transformers and even some inductors and capacitors  to boot in the plate circuit.   The crazy thing is that the amp 150 is only dated one year later than the amp 149 (they are both in the downloads, Pat L posted the amp 150 photofact) the one being 1956 and the other one 1957 and yet the schematics are so different.  The speaker connecting plugs seem identical and it looks like the amps could be switched with each other without any rewiring.
      Bills picture looks like his serenade has the amp 150. If you look at the amp 150 photofact front page picture and mentally rotate it so the 5U4s are in front and the three electrolytics are on the left, you can see where the 5U4 would hide the treble amp single ended 6V6 and you can see the 6AT6 treble preamp tube is right next to the filter cap. The 150 has 5U4s while the 149 had the smaller 5Y3s.
       I'd love  to hear the two amp circuits just to see if they had different sound characteristics. The one had separate amps and negative feedback from speaker windings back to the preamp cathode, the other had plate to grid feedback through the driver transformer. But maybe the older circuit sounded better 

TC Chris

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Re: FS Magnavox Serenade
« Reply #20 on: October 20, 2018, 12:04:30 PM »
I just looked at them both.  The Amp 149 has a tapped secondary on the LF transformer, with a section of the secondary to ground. What's that all about??

Chris Campbell