Emerson 540A restoration

[wa2ise]

Originally Posted by bob91343

I just want to make a philosophical observation. I am an old guy and these radios were current models to me. I looked at them with disdain even then, thinking how cheaply can something be made and still have it work. The workmanship, design, and component quality was of the lowest order, and the hot chassis exacerbated that.

It's a tough set to work on for sure. I'm having to peel away layers to replace the old caps.

My father, who would have turned 97 years old last Friday, hated Emersons. His complaint was that you'd sometimes have to remove some parts just to get at parts buried deeper down. Another factor was that his mother in law owned an Emerson 708 AA5 radio. Back in the early 70's I was in high school and was trying to fix that set. My father berates me for spending time on it "That radio is a piece of trash". He had the standard issue mother in law-son in law relationship Anyway, I never could fix that radio, today I know (from what I remember of it) that the IF transformers had silver migration disease. But that wasn't on my radar, problems had to be wax caps (find the bad one) or a bad tube.

That IF transformer below deck is a really ugly design.

[old_coot88]

Originally Posted by bob91343

A pin drive speaker is, as I recall, a magnetic unit. The horseshoe magnet had an armature that was a thin rod, or pin, that connected to the center of the speaker cone, which was a complete cone down to the tip.

It also eliminated need for an output xfmr, since the coil was high enough impedance to serve as plate load of the output tube.

I told you I was old!

I resemble that remark.

[Reece]

The pin drive speakers were used where the field coils of electrodynamic speakers were impractical due to power requirements, as in some farm sets of the thirties, where battery power needed to be conserved. This type of speaker was abandoned once good Alnico magnet PM speakers came along in the early forties. Interestingly, at least one transistor radio, I believe a G.E., used a pin drive speaker due to space requirements, in the early sixties.

[dieseljeep]

Originally Posted by Jeffhs

I cannot for the life of me imagine how a 2-tube radio could work, even as a TRF set. My grandmother had a 1948 GE TRF clock radio, but that set had four tubes, which makes more sense to me for a TRF radio. The only problem, at least with my grandmother's set and a 1936 Silvertone table set she had, was that these radios would pick up extremely strong stations on at least two points on the dial. Her radios were at her summer cottage, which was located five miles from a 50kW station, so you can imagine how strong that station was at that location -- it came in like gangbusters.

BTW, what is a pin-drive loudspeaker? I am familiar with PM speakers and field-coil ones, but pin-drive speakers are new to me. (Shows my age -- I am 56 years old and hadn't even been thought of when TRF radios and pin-drive speakers were new.)

BTW (2): Thank goodness resistance line cords (aka "curtain burners") are no longer used, having been replaced many decades ago (before tube-type radios were phased out in favor of transistor sets) by actual dropping resistors on the radio's chassis. I hate to think of how many house fires may have been caused by resistance cords which were too close to very flammable curtains.

Thanks much.

The radio in my entry was a two tube radio, but the tubes were the early dual purpose tubes. The RF amp and power detector was a 12B8GT. The rectifier and output tube was a 32L7GT. IIRC, the tubes were sourced by Tung-sol.
Basically it was a typical TRF of the day.
Re: the resistance line cords. Like everything else that can be misused and abused, the cords were no more of a hazard, than any other heat producing product of the day. The higher wattage ones were insulated better. They looked like iron or toaster cords of the day. If in good condition, they only got warm to the touch. Not hot enough to cause a fire.

[bandersen]

It's not quite so cramped after a recap.


I also installed a polarized plug with the neutral going to the chassis. The power switch was rewired to be on the hot side and 1/2 amp fuse added.


It plays surprisingly well
The chassis sure gets hot though. It seems the brass shield collars around each tube base draws a lot of heat into the chassis.

[Jeffhs]

What is the best (or safest) way to connect a polarized line cord to an AC-DC radio or TV currently using a non-polarized one? Every one of my antique radios, including the Zenith H511 on which I replaced the line cord, has a standard cord and plug; the latter can be inserted in the wall socket both ways, which could create a shock hazard if the plug were inserted such that the hot side of the AC line was connected to the chassis. However, the Zenith radio, and all my other AC-DC antique/vintage sets, seem well enough insulated (if the back cover is well secured to the cabinet and the knobs are snug enough on their shafts that they cannot be removed without pulling on them) that this doesn't seem to be a problem. I am only asking about the polarized plug so I will have the information available if and when I eventually decide to replace the cord or plug.

Thanks.

[bob91343]

I believe that the wide prong on the polarized plug is connected to the cold, or low side of the line, so that's the one to set up to go to the chassis.

However, having said that, you can't trust that your outlets have been wired correctly, so it's still dangerous.

I have pondered this situation for years and have not found a satisfactory solution, short of using an isolation transformer. However, that isn't so hard to cobble up from a pair of filament transformers back to back. You only need, for most of these little sets, 20 Watts or so, which can be gotten from a pair of 6.3 V 3 A transformers.

[dieseljeep]

Originally Posted by bandersen

It's not quite so cramped after a recap.


I also installed a polarized plug with the neutral going to the chassis. The power switch was rewired to be on the hot side and 1/2 amp fuse added.


It plays surprisingly well
The chassis sure gets hot though. It seems the brass shield collars around each tube base draws a lot of heat into the chassis.

If any radio needed a new power cord, it was that one. I was surprised to see it had the original one. Looked like the really early type plastic insulation and all twisted up. The plug looked like a replacement, as well.

[dieseljeep]

Originally Posted by Jeffhs

What is the best (or safest) way to connect a polarized line cord to an AC-DC radio or TV currently using a non-polarized one? Every one of my antique radios, including the Zenith H511 on which I replaced the line cord, has a standard cord and plug; the latter can be inserted in the wall socket both ways, which could create a shock hazard if the plug were inserted such that the hot side of the AC line was connected to the chassis. However, the Zenith radio, and all my other AC-DC antique/vintage sets, seem well enough insulated (if the back cover is well secured to the cabinet and the knobs are snug enough on their shafts that they cannot be removed without pulling on them) that this doesn't seem to be a problem. I am only asking about the polarized plug so I will have the information available if and when I eventually decide to replace the cord or plug.

Thanks.

I always felt, that if the radio was U/L approved, it didn't have to be altered. Especially if it was totally recapped, as the line isolation capacitor was replaced as well.
The important ones to rework, are the Hallicrafters AC/DC type, metal cabinet sets, as most of them weren't U/L approved and definately a shock hazard.

[bandersen]

Hmm, I don't think I've encountered a line isolation capacitor before Would that be a cap in the AC line between the plug and the rest of the radio ?

Or are you referring to an AC line filter cap ?

[bob91343]

That's a capacitor between one side of the power line and the chassis, usually with a high resistance resistor. A poor solution to a problem that never should have existed.

[Reece]

The whole business of making AC/DC radios safe leads to a series of compromises. If you have a true hot chassis set, you have a chance of the chassis being hot depending on how you plug it in. With a polarized plug routing neutral to the chassis, you're OK as long as your house receptacles are wired correctly. Most sets have the power switch piggy-backed to the volume control: it's better for hum reduction to have the neutral line switched but that would put the chassis hot. What most manufacturers ended up doing later on in the history of AC/DC sets was to use a floating ground with cap and resistor in parallel to chassis. You can still get a tingle from such a chassis, so to avoid that they used methods of mounting chassis where no exposed screws are hot or "warm," and lovely maddening captive knob arrangements like Zenith used. Another way I have used is nylon undercabinet chassis screws to replace metal ones on table sets.