[Arran]

Vlad;
You may have noticed that Motorola greatly simplified the chassis, and cabinet layout on the model you bought. They went with a more conventional layout with all of the batteries stored below the chassis, and all of the electronics in the chassis, rather then congregated all around the main chassis. One drawback might be the silver mica caps in the IF cans, by then Motorola was using the 3/4'' square Automatic style IF transformers I think rather then the round ones. One thing I will say about every Motorola radio I have had, they usually performed well once restored, and they though of things like disconnecting antennas, and speakers, for servicing.
Regards
Arran

[klondike98]

Thx Vlad.

[Vlad95]

Arron,
Yes, I can see the differences in the interior design, but if you compare the schematics, they look very similar. They are also very similar externally.

[Arran]

Vlad;
Yes it's very similar, Motorola obviously wanted to get the most use they could out of the dyes used to stamp out the steel cabinets, all they had to do was put a new front panel, and door on to disguise it. I guess you could say that the chassis was a refinement of the 1948 model, electrically they would be very similar, pretty much all "three way" portables from that era are, some would have a tuned RF stage, others not. I think that the largest change was that many started using a 3V4 audio output tube, which gave better performance then the 3S5. There is a green version of your set out there as well, I will have to see if I can find one.
Regards
Arran

[klondike98]

Some good news on this set. I took Vlad's guidance and fed audio through the 3S4 and heard it OK. It seemed a bit off in sound but I moved on to the 1S5 and got absolutely nothing out. I checked voltages around the 1S5 and realized I had 60 volts on the plate when there should only be 25 volts. I rechecked all the connections I had made in recapping to be sure I had not connected one to the wrong place but all seemed OK. Next step was to reflow the solder on the pin 5 plate connection. After that it seemed to play reasonably well and with some clean up of the volume control and the tuning capacitor to eliminate most of the static it aligned properly and is playing well.

The R-4 replacement resistor (200 ohm, 5 watt) gets pretty hot so I may see if I can fit in a 10 watt but I think its going to be mighty tight. One think to watch if you are replacing the power cord on this set it to not make it too long. I put in a 6 foot cord, forgetting that when the set is all closed up and playing on battery, the power cord plugs into the chassis in a way that switches it over to battery operation and you then coil the cord around the A battery holder tabs. I had so much cord that wrapping it up and shutting the case was not working so I cut it down to about a 4 foot power cord. To be honest, the metal case along with the hot chassis seems kind of dangerous so this is best played with the battery anyway. Once its all reassembled, I will be checking to ensure that the chassis is not connected to the metal case. Unfortunately you can not use a polarized power plug on this and still get the plug to fit into the ac/battery switch.

I still need to get the battery snaps installed, do some additional restoration/clean up on the case and then hopefully this one will be finished.

[klondike98]

I need some help understanding what I'm looking at with this radio. It is playing just fine, better on battery (less noise), but fine all around. The issue is that I don't understand why I'm seeing 120v AC between the radio case and ground (my shop ground). I can not find any short between the radio chassis, the ac power leads or its outer case and the hot chassis depends on whether the set switch (operated by opening the front panel) is ON or OFF and which way the power plug is inserted. (In battery mode, there is no voltage on the chassis or case at all.) I'm sure I'm missing something but scratching my head on this one...

Here's the data:
[Image: https://www.dropbox.com/scl/fi/87jh8vd0m...chcu&raw=1]

The schematic is:
[Image: https://www.dropbox.com/scl/fi/jtk0o26aw...rpkt&raw=1]

[Vlad95]

Capacitors C5,6 connected AC line with chasis all time independed from switches S1,2 status.
And 120V is leek on chassis througt capacitors.
This is a big and dangerous problem with all the old transformerless radio designs.
Just a strong piece of advice - never use these radios from AC power without a special 120v - 120v isolating transformer

[morzh]

I think you are seeing some voltage due to the caps connected to the case.
Not sure its hould be 120AC, but there should be some.

I also wonder if rotating the plug would change the value.

[RodB]

According to the schematic the caps should be connected to B- not the chassis. The only components connected to chassis are the rf tuning capacitor/coil, E1 wave trap and the speaker.

[Vlad95]

RodB
You are right. It is my mistake. There is no direct or capacitive connection between power and chassis.
You need to check if there is parasitic capacitance or resistance leakage. And what is the possible leakage current to ground. In case of parasitic capacitance, it will be units of milliamperes. If there is a resistance leakage, for example in an audio transformer, it can be much worse.

[klondike98]

Thanks guys! Some things to look into for sure. While it’s a neat looking radio I think it’s not really designed well. The chassis is very tightly fitting in the metal case and it’s just some insulating board separating it in multiple places. I’ll get back on what if anything I can determine is going on.

[klondike98]

Mike, I did reverse the power plug and the results are the opposite from not reversed. It’s in the chart data. Hopefully I can do some more checking later today or tomorrow.

[morzh]

Bob


Opposite meaning, no 120V AC?

[klondike98]

OK I definitely have some capacitive and resistive leakage. Here's some additional measurements:

[Image: https://www.dropbox.com/scl/fi/wssh2zuhx...07z8&raw=1]
NC=no continuity

(I should have said it earlier but all these measurements are of course with the set unpowered) I can access B- point easily with the set in the ON position because I know which power lead goes to the B- on S-2 ON-OFF switch. The other power plug lead goes to the diode anode. Not sure what I can do about the capacitive leakage but the resistive 4Meg definitely should not be there but hopefully I can track that down. I don't look forward to that on this set! Looking forward to your thoughts, thanks for the help.

I hate to think about it but I could just cut the power cord out, leaving the plug in so it is in battery mode and only use it on battery mode. If I can't get the case isolated that may be my only solution because I'm sure not going to leave it place and have someone get hurt.

[klondike98]

Mike, opposite as in with the plug normal I get 120v to the case and chassis with the set switch in the Off position. With the plug reversed I get 120v on the case and chassis with the set switch in th ON position. I think it has to do with which lead is connected to the B- at S2.

I will be taking the chassis out of the case and doing some more to track things down. I’m wondering if my antenna hinge fix is somehow causing problems. We’ll see.