Reason why RCA designed AC/DC sets - Videokarma.org TV - Video

Jonathan · #1 12-22-2005, 10:34 PM

I have a couple radios from RCA from the 30s and 40s that have SW and BC bands and have no power transaformer. Why did RCA come out with these and not seal up the back so wandering hands or the inexperienced repairman wouldn't touch it?

Were these sets made for customers that couldn't afford transformer sets or compatibility with both AC and DC? I prefer transformer sets as I don't have to use an isolation transformer all the time. I guess multiband radios were expensive and using a live chassis kept the cost down.

Thanks.

Jonathan

Celt · #2 12-22-2005, 11:10 PM

Quite simple. Back then some rural areas still didn't have electricity or what we would consider to be reliable electricity. REA (Rural Electric Association) was well known for their flickering and intermittant power supply. So, people would buy batteries for their radios and use them sparingly (weekends). They weren't sealed up in the back because they needed ventilation and they weren't probably all that reliable either.

blue_lateral · #3 12-22-2005, 11:44 PM

I think some areas actually had dc power in those days. A transformer set would have been useless. The low cost probably made it catch on where it wasnt needed.

I think "hot compared to what" would have been another issue. It wouldnt have been like today where the electrical box is clearly grounded, and the neutral is at the same potential as ground. The chassis is clearly hot compared to all sorts of stuff around you, at least if the plug is in a certain way. Then, a lot of houses that were wired in the teens or 20s had 110v drops from the distribution system. Nothing was grounded. They used to fuse the neutral. That sounds insane today, because the neutral fuse could blow leaving the hot hot. Then, though the neutral was coming from the distribution system and could be a little bit hot. Probably not as hot as the hot. There could be some voltage difference between the neutral and say a water pipe in the house.

110 doesnt usually bite that bad, and it was fairly common to have 400v (or more) floating around in a transformer set of that period. I doubt those sets were considered the most dangerous at the time.

Also, it was probably assumed you werent going to lick it or take it in the bathtub with you.

Today, that would be the content of the instructions. Back then, they probably told you how to use the set.

John

Mark W. · #4 12-23-2005, 12:09 AM

there are still some thousand+ edison electric customers in New York that recieve DC current to this day!

Jonathan · #5 12-23-2005, 01:48 AM

Wow, I am suprized that even today there is DC! The transformer sets do have around +400V on the B+. I guess I'm more used to transformer sets. As long as the chassis is connected to neutral and I use a polarized plug I should be OK. Another reason is that I like to have the chassis out and playing rather than in.

Jonathan

Chad Hauris · #6 12-23-2005, 01:53 AM

Most of the later 40's and 50's RCA, Philco, etc. AC/DC sets have an isolated circuit ground with a capacitor coupling the chassis to the power line for safety. Most of the Zenith tube type table sets run the power line right to the chassis but have it completely enclosed with insulators on the knobs and mounting screws.

I have seen schematics for some older AC/DC sets with the power line going straight to the exposed chassis, have not had to work on any. You probably could improve the safety of such sets by using a polarized cord but still I would personally use an isolation transformer, it's not worth the risk of a shock from a live chassis, and even the neutral can have a potential above earth ground and cause a shock.

I don't believe that DC is being used for residential power today! Most electronic stuff today has a switching power supply that uses a voltage doubler circuit and will not work on DC.

Sandy G · #7 12-23-2005, 06:10 AM

Yeah, IIRC, it was 1952 before EVERYWHERE here in Hawkins County got "juice". There was a huge market for sets that would run either on batteries or AC out here in the boonies for a long time.-Sandy G.

nasadowsk · #8 12-27-2005, 12:32 AM

DC is still delivered for industrial uses in NYC. Con Ed still supplies it. There are still a good number of pure DC elevators in NYC, and the controller firm I worked at prior to my current job used to build 2 or 3 new controllers for DC elevators a year. They were basically the last to do 'em though.

Residential? I doubt anyone gets DC anymore...

Chad Hauris · #9 12-27-2005, 02:40 AM

That's interesting that they still supply DC for elevators...I think there are some elevators here that are using DC motors and are using motor-generator sets to provide the DC.

Bob · #10 12-27-2005, 02:47 AM

Downtown Manhatten - Delancy Street area - many buildings have only DC power.

No hum on any equipment.

OvenMaster · #11 12-27-2005, 04:31 AM

Do any of these buildings have human staff of any significant number? Sure, there's no hum on anything, but how do they heat up their lunches if they can't fire up a microwave oven? These can't be residential buildings. Try and find any DC-only kitchen appliances.
Tom

vintagecollect · #12 12-28-2005, 08:58 PM

AC/DC to save on transformer costs. I can see this to save money since no xfmr needed. They were expensive then to make, maybe a little cheaper then today since mass produced, and certainly kill many restoration projects today if radio isn't worth investment. A lot of copper and labor = expensive new part. Radios were taking a backstage anyways with the wide spread introduction of TV after WWII.

kx250rider · #13 12-29-2005, 11:25 AM

There must still have been non-110 areas of the US in the early 80s someplace... Because when I was working for a Zenith service dealer, we accidentally ordered a replacement TV module for 25" color set that turned out to be for 32V AC/DC supply. Weird! A radio collector told me that 32 VDC was the "farm power" standard in the Midwest at one time. Only saw that once though, and it isn't in the parts list anymore.

Charles

Chad Hauris · #14 12-29-2005, 12:21 PM

32 volt DC is the voltage used by Wincharger wind-powered generator systems...have never seen any modern day equipment using it though. I would think most people using wind or solar power today (or in the 80's) would be using 12v or 24v dc and and inverter to provide 110 AC for TV's and such.

Charlie · #15 12-29-2005, 01:32 PM

Many of the WWII T-2 tankers I used to work on 10 years ago still had the old DC power outlets in the rooms. I'm sure they probably weren't live... I never thought to put a meter in one and check. Those ship were all DC in those days. Sailors really didn't carry any electrical items on board back then... they only carried booze and lots of it. But, if you brought on anything electrical, it had to be DC powered.