1959 Magnavox Trapezoid Console
 

Acquired this sometime ago.

Looking to use it as an iPod amp or otherwise. Legs are no longer attached. They did not survive storage well. Help wasn't aware stacking heavy boxes not welcome on this...

Unlugged the record player hooked up iPod shuffle. Had to turn on record player to turn on amp. Sounds pretty decent.

http://homepage.mac.com/chronotek/magnavox.jpg
http://homepage.mac.com/chronotek/magnavox2.jpg
http://homepage.mac.com/chronotek/magnavox3.jpg
http://homepage.mac.com/chronotek/magnavox4.jpg
http://homepage.mac.com/chronotek/magnavox5.jpg
http://homepage.mac.com/chronotek/magnavox6.jpg
http://homepage.mac.com/chronotek/magnavox7.jpg

Diagram on back seems to me that the red/yellow/black wire goes to the record player start/stop switch. Haven't investigated further.

Best suggestion to put a switch on the amp directly?

Red/Yellow connected turns it on, Red/Yellow disconnected stops?

Thinking about keeping the grill boards intact with speakers and using them open baffle.

Also thinking the speakers are coaxials?

I could in theory use a crossover and drivers from a dismantled box set and just run the outputs to speaker from amp to my crossovers?
I'm assuming there is no crossover in this model? Haven't torn it apart completely yet. But will soon.

Suggestions welcome to properly get this amp to work without the record player.
Number hidden behind red/yellow/black wires is a 9 so it's 6 50 9 other number is 80-02-00

Speakers are decent? Jensens or no?

Best guess on model number is 180261E or 180261F or 1?0261 E 1?0261 F where ? = cannot identify.

Channel 1 is L, Channel 2 is R? Black is Left, Green is Right?

If so I've got it backwards...

Thanks!

Sorry I can't answer your questions,
But that is way cool........

Trace the wires that lead to the switch on the bottom of the turntable. You should be able to cut them and put a switch on them. I've seen toggle switches used in this way. BTW, what are you gonna do with the TT?

Good suggestion on the wires. I know they go elsewhere and the switch moves lever/gears to do something in another location. Have to finish dismantling it all. I sent you a PM on my plans for the TT - can't break AK rules.

Another hi-fi set with 50EH5s
 

Your Magnavox console should sound great with those 50EH5s in the output stages. My Zenith MJ1035 FM stereo radio also has 50EH5s in its output stages (one per channel), with a 12AX7 preamp, and sounds absolutely fantastic, even though the volume control is intermittent as all get out (if I pull outward on the control shaft I get more volume than I'll ever need, although the radio plays at normal listening volume with the control set where it is at the moment--so I won't do any more with it or to it until or unless something goes wrong, like a tube filament burning out).

In case you ever need to replace one or both of the output tubes (or any tube, for that matter) in your console, be sure to replace them with the same type Magnavox put in there in the first place, when they designed the unit. The 50C5 may work in a pinch as a substitute, but I wouldn't count on it; it is best to use 50EH5s to replace 50EH5s. Another good thing about the 50EH5 is that it is actually cheaper to replace than a 50C5, as I found out from an AK member (electroking, in Montreal) recently, in response to an inquiry I had made about substituting 50C5s for 50EH5s. I found this rather odd, as I had thought it would be the other way around; that is, the 50C5 would be cheaper than the 50EH5.

I also have one of those!

I haven't gotten around to doing anything with it yet... but one concern is that this is one of those unit that has a LIVE CHASSIS... i.e, no power transformer. You need to exercise extreme care in connecting other out-board things to this... the danger for electrical shock is pretty high!

I was thinking of modding mine, with a power transformer... depending on which one I pick, it might wind up "boosting" the output a bit. Would be interesting to see what I could get out of it, changing over to 6AQ5 output tubes... but, that's a project that I will have to get around to, when I get around to it...

Regards,
Gordon.

Now that's some useful information. Is there a way to remedy that live chassis problem easily? Is it safe to assume that many of these Console tube units are live as well? Suggestions to remedy this are welcome.

Luckily I've learned long ago connections/tinkering is best done with power off, and also with devices not plugged in for further assurances that all is relatively safe.

The best way to remedy the live chassis problem is to use an isolation transformer between the wall plug and the AC input of the amp. Antique Electronics Supply sells these.

I have seen a few cheaper consoles that had a transformerless hot chassis. These were usually record player only units or low end AM or AM/FM/phono combinations. I just gave away a BOTL Zenith tube AM/FM/phono console from the mid '60's with a hot chassis. All of the better consoles used a power transformer chassis.

Most power transformer sets used capacitors either across the AC line or connected between one side of the AC line and the chassis. If an "across the line" cap becomes leaky or shorts, it can explode and/or blow the fuse in your house. If a "line to ground" cap shorts, you'll have AC on the chassis! It's best to replace these caps with modern "safety capacitors" that are designed solely for AC line bypass. www.radiodaze.com sells these types of caps as well as just about any other type of capacitor that you might need for tube electronics.

Hmmm...

So an isolation transformer would mean a new housing for this amp would be a good idea?

This might end up being too much of a project for me at the moment. I was looking for a quick remove the amp and use it kind of thing.
Not keen on potential BZZZZT scenarios...

What if I mount it to a block of wood, and put a plexi vented cage around it?

With an isolation transformer, you just plug your power cord from your Maggie into the transformer and then the transformer into the wall receptacle. You don't have to modify your amplifier if you don't want to. The isolation transformer can be "outboard". There is probably room inside the Maggie cabinet to mount the transformer. Some isolation transfomers may be intended for hard wiring rather than plug-in applications.

Rather than remove the speakers and speaker boards from the cabinet, you are going to have better sound by leaving them in there the way they are. Speakers need acoustic isolation between the front and back of the cone in order to produce bass notes, and generally speaking, the longer the acoustic path between the front and the back of the cone, the better. A speaker sitting out by itself with no baffle, or only a small board baffle, and no enclosure, won't have much bass.

I would say that these speakers aren't coaxial, which means that there is a separate tweeter mounted coaxially inside the woofer, with its own voice coil; but that they may be dual cone with either a small cone or an aluminum or hard paper dome over the center of the main cone, for the higher frequencies, but all actuated by the single main voice coil. I don't see any second voice coil connections on the speaker terminals.

Reece

1959 Magnavox Portable Unidentified Component
 

I've got a Magnavox similar to the Trapezoid but in a portable suitcase. It has an amplifier number 8001-10. I'm in the process of recapping the amp and ran across a component that I'm unsure of. I believe it may be Wima cap. It is in an orange flat pack, two leads with a W and 22 stamped on it. Anyone know if it is a cap and is the value in uf or pf? I'll try to attach a picture of it.

That looks to me like a wire-wound power resistor in series with the silicon rectifier. Check it with an ohmmeter - if it's anywhere close to 22, leave it be...

It could be a capacitor, but on the other hand it could also be an encapsulated component combination unit, also known as a couplate. I have a Zenith radio with two components that appear similar to what you describe, one for the stereo FM decoder and the other for another function that escapes me at the moment. However, since the flat pack component in your Magnavox amp has only two leads, I'm hesitant to even guess what it is. I have never seen a capacitor in a squarish flat package--round, yes, but never square. The W and 22 may be value markings, but I'm not sure. :scratch2: If there is a little diagram taped or pasted onto the underside of the chassis, your mystery component is probably a couplate.

Note: Ooops. I just read Tom Bavis's post, in which he described the component you're seeing as possibly being a wirewound resistor, very possibly a fusible resistor. If it's in the power supply, it may very well be a fusible "sand resistor" (another name for a fusible, probably named that because of its sandy appearance), designed to open in a hurry under a severe current overload. Many series-string televisions of the 1950s had these; I remember my folks' second TV having a 33-ohm sand resistor in the power supply, near the selenium rectifiers. My Zenith MJ1035 stereo FM radio has a 33-ohm fusible in its power supply, only that one is much smaller than most sand resistors and is enclosed in a ceramic tube. Seeing all the sand on the component shown in your attached thumbnail almost convinces me as well that the thing is probably a wirewound fuse resistor.

Ah hah!
 

Just ohmed it out and it measures around 24 ohms. I think I'll take the leave it be for now advice and research it further. Thanks for all your help! Also, thanks for the safety advice about the lack of isolation. Does anyone know if these amps are listed in Sams?

That's a specially designed "fusistor". Combination fuse and resistor. If it does burn out, just replace it with a regular power resistor and an in line fuse holder with fuse. 1/4 amp slo blo should be about right.

Funny that they put a low-noise 7025 as the input tube. Any old 12ax7 will do
in this application. The factory may have gotten a special surplus lot of 7025s,
or the tube distributor tipped the design engineer so he would specify the higher
grade tube, who knows?

Magnavox tended to use the best stuff, even on their low-end products. I worked there for 13 years, a little later than tube amp days, but still back when pride in your work was a factor over raw profit. Doubt it was a surplus buy or greasing a buyer. A phono cartridge needs a lot of gain, and is inherently noisy, so the 7025 was a good design choice there.

It's probably too much gain for your iPod. The iPod will overdrive the 7025 and it'll distort. You might want to try a 12AU7 instead. 12AT7 next. 12AX7 last. 12AU7 probably. If the 7025 tests new, selling it on that ePay place will pay for your isolation transformer (they can be found on that ePay place too).

I have a high-end Magnavox mono phono from the pre-stereo days of circa 1950. 12AX7 input preamp driving a quad of 6L6's (parallel push-pull) into 5 speakers, in a nice hardwood piece of living-room furniture. I don't use it for vinyl but occasionally plug my Fender Strat (guitar) into it. It screams quality. I think your S/E 50EH5's will "suggest" quality and you'll be pleased with the outcome if you go for it.

Your hot-chassis issue won't quite be solved by enclosing the amp in plexiglass and wood. If the chassis is hot, the cable shielding will likely also be hot, meaning the ground-side of your iPod will also be hot. Which may or may not be the case of your iPod. Risk is there for shock handling it, risk of damaging the iPod too.

Safety #1 is the isolation transformer. Lesser but cheaper alternative #2 is .022uFd blocking capacitors in the line leading to your iPod. The cap solution works for guitars, but might be a fidelity issue on your iPod up in the highs or way down in the lows. I haven't gone there, maybe another AKer has experience here.

Not to start a big argument, but the ceramic cartridge used here does not need
a lot of gain, and if a source is noisy, a low noise tube is not helpful. The 7025
is fine as a preamp tube if a magnetic cartridge is used, but I maintain that any
good quality 12aX7 will do perfectly here.

Good day to all.

The hot-chassis issue is not restricted to Magnavox as any series-string radio, TV or phono amplifier will have a hot chassis, depending on which way the plug is inserted in the wall socket. I have a Zenith MJ-1035 stereo FM radio with phonograph inputs, supposedly isolated from the line by a capacitor. However, I would not think of connecting anything to those jacks without replacing that isolation cap first, and even then I'd think at least twice before plugging any kind of modern electronic gear such as an iPod into them. As was mentioned, this is (or could very well be) a disaster waiting to happen. I wouldn't plug anything other than a stereo turntable into those jacks, even after replacing the isolation cap. The risk of shock and/or equipment damage, in that order, is too great.

BTW, the preamplifier stage in my MJ1035 is in fact a 12AX7, the output stages are 50EH5s, and the radio sounds absolutely great, except for some background hum (probably a loose or missing ground connection). Zenith obviously did not skimp on much of anything, IMHO, when they designed this set, the speaker issues (which have been discussed at length in this forum) notwithstanding. I personally cannot tell the difference in sound between the MJ1035 and my C845 (the latter has the same speaker system as the MJ), except that the MJ sounds more mellow than the C845 because of the MJ's larger cabinet. I have found, after doing some research on the MJ1035, that the radio uses the same chassis (11J01) as Zenith's console stereos of 1965 vintage. I'm not surprised. This chassis has "high fidelity" written all over it, not to mention a front end hotter than a firecracker (I was listening to CBC Radio One from London, Ontario, Canada on my MJ1035 this afternoon, and I can get stations from Windsor and other SW Ontario cities, not to mention Detroit, Toledo, Ohio and Erie, Pennsylvania on this radio as well from my apartment in northeastern Ohio, using just a six-foot length of wire as an antenna).

The only thing I wish Zenith had included on the MJ1035 is external stereo speaker jacks. If this set sounds as good as it does through its own speakers, I would think it would sound as good as any hi-fi system if it were driving high-efficiency speakers. The only problem I can see with using any other speakers with an MJ would be that the impedances are non-standard; the main speaker is 4 ohms and the HF driver is 46 ohms. While replacing the main driver with an 8-ohm speaker won't harm the output stages (it will only reduce the output volume a bit), the tweeters are a different story. Putting any type of speaker of less than 46-ohm impedance in this position in an MJ1035 (or any type of audio equipment, for that matter) is asking for trouble, as the use of a speaker of lower impedance than the original will damage the output transformer and possibly other parts of the output stages as well.

You're right Jeff, I think plugging in an iPod directly might be unsafe for it although I've done it with no harm, yet. I listen to my iPod with an FM transmitter {when I actually use the damn thing} I hate using those little headphones. Those C845s are nice, I'm listening to the Drive in Chicago right now, these radios are some of the best Zenith made. That hum issue with your MJ1035 could be a 'lytic going bad, I've had a couple Zeniths do that over the years.

Ok, no argument. I just know how those engineers thought, and they wouldn't have designed a 7025 where a 12AX7 would do. Agreed a low-noise tube would not fix cartridge noise. Perhaps in this particular cabinet design, the amp chassis happens to be mounted too close to the speaker's acoustic path and when testing the betas of this thing, the engineers got some ringing somewhere. Or maybe the speaker and amp structurally shared the same "sounding board" element of the cabinet. Whatever it was, they chose a 7025 to address it. My point is, I don't think Emerson or Wards Silvertone or GE went to that level. Magnavox went the extra mile. All their stuff, to this day, is better than the average bear.

I know this is a pretty old thread now but I just picked up a maggie suitcase phono that uses this same amp. I'm wondering if you ever recapped yours? I got together the caps to swap out the old can but I cant find the markings on it anywhere. I thought maybe somebody would have some insight on this ? theres a cardboard cover over the can but its just the same marking under that.

Quite typical to have a 20-50 ohm resistor in series with a diode power rectifier.

Reece