Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on May 15, 2014, 02:22:22 pm
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Boy i sure got some old cool amps in here this week. This Magnasonic is in pretty decent condition. One channel not working now working. No Tremelo as of yet. Footswitch is working and good.
1961 Brownface Princeton & Magnatone M4 also in the wings/
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Even though I am a reverb fan, love those old Princetons. They are just such classics.
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Looks like a sturdy build, point to point, where was it made and what year?
Is it basically a tweed Deluxe (5E3) but with a tone for each channel and trem? Cathode bias output power stage?
Where's the trem applied, the power tubes?
Brad :icon_biggrin:
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That looks like an incredibly solid build! If they saved money, it was by using the open-ended chassis (easier/cheaper metalwork) and on the C12R.
The oil coupling caps throughout the amp are very likely fine unless they are visibly leaking oil. The dog-bone resistors are also likely good, really only leaving electrolytics or low tube gain as likely culprits.
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The amp sounds great. Plenty loud. I have not looked for a schematic as of today. (3) 12AX7 (2) 6V6GT (1) 5Y3. Back soon
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Looks like an early sixties Japanese build.
I look forward to seeing pics of the M4.
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The input jacks are stamped JAPAN terminalg. The handels on both the Magnasonic and Princeton are flexable as a well oiled piece of leather and almost new looking though they are original. The M4 will be opened up in a few days. Im curious too to see those varistors once again. herNo working Vibrato in the M4.
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Quick Google search indicates magnasonic might be linked to unicord and univox. Makes sense. I think unicord had the chassis and circuits assembled in Japan and then fitted transformers, tubes in New York. You might check out some early univox schematics with same tube compliments.
Nonfunctional M4 vibrato, probably the oscillator. The varistors rarely fail.
Great variety in these three amps!
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I have the the tremelo working. Dirty preamp tube sockets. Sounds nice. Amp is surprisingly quiet considering the age of the power supply caps
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I have the the tremelo working. Dirty preamp tube sockets.
That's pretty funny! The components used are types that seldom fail, so it's nice to see that perception was correct!
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I was going to say HBP that i wish they all were that simple a fix. But then we wouldnt have the challenge or knowledge to repair the next one. Nice amp! :icon_biggrin:
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This calls to mind the old phrase; 'built to last'. :l2:
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That makes me think of the 1940's Army transport truck i helped restore back in 1974 or near that time period in P TECH. Back then almost all military and taxi cabs used chrysler engines and heavy duty axles,trannys. Bertrams (boat) had 1" + fiberglass hulls. Everything was over built and will be here 1500 years from now. Thats if some axis of evil force doesnt crush the earth like a tin can.
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Just found out a friend of mine has a Magnasonic - looks similar/same as yours. Do have a model number? He said he can't find one on it. Cheers!
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Just found out a friend of mine has a Magnasonic - looks similar/same as yours. Do have a model number? He said he can't find one on it. Cheers!
Err, this thread is 10 years old. =)
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Just found out a friend of mine has a Magnasonic - looks similar/same as yours. Do have a model number? He said he can't find one on it. Cheers!
Err, this thread is 10 years old. =)
Regardless, Plexi50 is still active here, and the photos serve as a reference.