I've just picked up a 1957 Super Magnasonic 294H monaural phono and AM/FM console. It has the typical amp-142 20W quad 6v6 amplifier that many folks here have rebuilt many times. However, instead of being the amp-142aa or amp-142ab variety that seems more common, it is an amp-142cc model.

Does anyone know the correct Sam's for the "cc" model, or at least know the difference between the "cc" and the "aa" or "ab" models?

My amp-142cc has two things that might make the difference. First, it has an output for a secondary set of external speakers, switchable from internal/external/both. Also it has a 6V lead that powers the chassis "on" pilot light. I don't know if the "aa" and "ab" don't have these for certain, but perhaps...

Also, I've been looking around this forum and elsewhere to review what others have done when rebuilding the amp-142, but was hoping to gather a concise list of typical mods or fixes for the amp-142 in one place. I intend to keep it installed in the console, so I don't need it converted to a standalone mono unit, but would like to cover all bases for increasing safety and performance that others have already figured out.

Thanks,
Al

First off let me say thank you for preserving a classic Maggie console instead of gutting it. I'm no expert by any stretch but I do have experience with this particular line of amps. The AA, BB, AB, CC etc designation generally referred to the cabinet model. You will find very little if any difference in the circuit. Replace the electrolytic caps along with any wax caps inside the amp. Check the resistors for any that are out of tolerance and replace as needed. You can increase the lytic values but don't go too high. You can also increase the cathode bypass lytic value to gain some bass response. One mod I did was to use metal film resistors. They tend to be less noisy in these amps. Carbon film resistors work well too. Replace the cathode bypass resistor as well but stick with the stock value. There are several possibilities with these amps but they sound pretty nice as is. I actually did a scratch built pair using all new Hammond iron and they sound fabulous. I'm now in the process of doing a full rebuild on another 142 using all high end parts along with the vintage Maggie iron. PM me if you need any help and thanks again for not curbing the cabinet!

Thanks, much appreciated.

I've heard that many folks have converted to a grounded three lead mains cable, and thereby eliminated some safety bypass caps that I've heard called "death caps".

Is there a brief description of what to remove and how to connect the new power cord. I assume the ground lead is just grounded to the chassis?

Thanks,
Al

I used the three wire cords on my scratch built amps (I call them Magclones). I used them mainly for the ease of a detachable cord. I did'nt use the ground lead. I've read that using the ground of the house's electrical system can introduce noise but thats probably debateable. Connecting a new electrical cord is straight forward. Trace the original cord to the amp. It should attach to a terminal strip with one wire tied to a lead of the power transformer(black wire). The other wire should lead to the phono switch or, in your console's case, to the switch on the tuner then back down to the amp. Un-solder the original cord from it's tie in points and solder in the new one. As for the "death cap(s)", I just remove them altogether. Have'nt noticed any adverse effect. These amps and countless others like them have existed for years with two prong ungrounded, non-polarized plugs and should be fine as is. The most important part is that you go thru it and replace the caps and out of spec resistors before you power it on. I have broken that rule with some Maggie consoles/amps and have been lucky so far but luck only lasts til you fry a vintage power transformer.

To answer your ground question.. yes connect the ground lead of the cord to the chassis.

That will instantly cause a ground loop on a Magnavox chassis, in many cases. All the components are signal-grounded to the chassis (RCA jacks, all the low-level signal grounds, etc).

Believe me, I've BEEN there. I've had to un-do it where it was done. You might get away with it in an original stand-alone console (as there's usually no outside components connected), but you definitely can NOT do that, if you use any other components that have three-wire grounded power cords, connected to the amp or preamp anywhere (say, if you splice in a connection for a DVD or CD player, cable box, or such).

Even in the console, I'd suspect you might wind up with more hum than stock...

Regards,
Gordon.

My entire stereo system is grounded through the tape recorder's 3-wire power cord and is completely hum-free. I really can't see a problem with this. I suppose there could be circulating currents if you have multiple components connected to multiple outlets on different circuits, so I would recommend using a single power strip as we used to do in radio broadcasting.

-David

As I mentioned before I'm no expert. I do, however, have 6 Maggie amps(169,4-142's,150) that have all had a 3 wire grounded plug at one point or another without any hum. Perhaps I have simply been lucky. Still learning new stuff but certainly not a beginner. I will power my Mags with two prongs from now on. Its what they always had anyways. Tried a 3 wire on my Zenith 10S669 and the hum was pretty bad. Switched back to 2 prong and it plays wonderfully with only a barely noticeable hum.

Apparently there arent many fans or owners of Maggie 142's. I'm working on a few mods that should help the overall performance of the 142. One of them is a constant current source. The other is an active tone control using a 12AU7 and adding a volume control. More on those as the project progresses. I can only assume that there is more interest in the two channel amps. The seem to fly off ebay for pretty decent coin. The last 142 I got from the bay was only $60 shipped. Thats cheap for good vintage iron and plenty of usable spare parts. The rather popular 185 usually brings twice that easily. To each their own. I love the mono Maggies!.. Along with my pre-war Zeniths. AA5's. Tombstones. Bakelite sets.. etc etc...

Grounding the chassis with an AC rated cap to a polarized cord works fine.
My 93-04-20 amp is totally hum-free with my system.

On the contrary! I've rebuilt pairs of them into stand-alone monoblock power amps. Sounded fantastic!

Also, I've used these chassis (132/142/150/179/etc), as basis for creating stereo 6L6 amps. The power transformer is usually big enough (made to run up to five 6V6s and a bunch of tuner/multiplex tubes) for PP stereo 6L6s. I add a second output transformer of the same type (I'm almost always looking around for spare 330024 output transformers), and re-work the thing for stereo PP with 6L6s (upgraded front-end for more voltage swing, less drive impedance, etc)...

I'm building one of these (on a 179 chassis) as a stereo integrated PP 6L6 amp right now...

Regards,
Gordon.

The earlier poster was right about the letters in a way.The first letter was a mechanical change from the origional design or the AA- chassis.An extra hole for a pilot light socket or speaker,moving the socket or an extra mounting hole would result in a first letter change.The second letter signifies an electrical change,usually a component value change or something like that.I'm not a wizard,just read alot and a copy of the Green 1955 Magnavox service big book is around here somewhere and thats pretty much what it says.The letters do follow cabinets to an extent as in a contemporary cabinet may have the pilot light socket near the output trans and be chassis AA but an early american cabinet may require this socket to be side mounted so the change in socket position would be BA-185 etc.I have to dig out the book as I may have this backwards but look the chassis over carefully.Feedback components were a fav for Magnavox to change too so be extra carefull with those!