And you thought Chinese mains adapters are sketchy.... - Page 1
Forum section: electronics / general

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 01, 2015, 04:54:43 pm
content: Check out this 240-110v converter that came with an old 9.5mm film projector a friend gave me to get going....

author: SeanB
author_rank: Super Contributor
timestamp: November 01, 2015, 05:04:44 pm
content: Original Phillishave had a converter unit to use it on 220VAC mains, which consists of a large ( as in the same size as the shaver) plug and socket that contains a massive wirewound resistor, complete with green vitreous enamel coating. Not as bad as yours, but at least that one doubles as a room heater and film drier. Genuine Asbestos there, probably mined in South Africa, and a lovely patina of rust as well..... Should have a lovely aroma of burning cobwebs mingled with silicosis if you power it up, though i think the projector will contribute it's own smell as well of cooking lamp and drying paper windings.

author: Len
author_rank: Frequent Contributor
timestamp: November 01, 2015, 05:05:28 pm
content: Quote from: mikeselectricstuff on November 01, 2015, 04:54:43 pmAnd it makes toast too!

author: tggzzz
author_rank: Super Contributor
timestamp: November 01, 2015, 05:05:56 pm
content: Did it have a mercury arc rectifier? The first and last one I saw was in my universities' student union, under the bottom of the open stairwell and used for the film projector.http://www.oobject.com/mercury-arc-rectifiers/twin-mercury-arc-rectifiers-from-the-doncaster-odeon-movie-theatre/8401/

author: G7PSK
author_rank: Super Contributor
timestamp: November 01, 2015, 05:09:38 pm
content: 1920 or 30's I presume. Come across that before with an old bell and howell projector. Problem was if the lamp blew the motor was over volts so you had to shut it down very fast. Replace it with a transformer you can get site transformers very cheaply. Back then many places in the UK were 220 to 250 volts DC so transformers were out.

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 01, 2015, 06:34:22 pm
content: Quote from: G7PSK on November 01, 2015, 05:09:38 pmThat is a very logical explanation why they would not use a transformer to go from 240 -> 110!But then I don't think the film projector motor will run on DC?

author: SeanB
author_rank: Super Contributor
timestamp: November 01, 2015, 06:51:02 pm
content: Quote from: PA0PBZ on November 01, 2015, 06:34:22 pmUniversal motor and 110V bulb, so it will run on DC or AC. The film speed is controlled by a centrifugal switch on the motor shaft that opens and introduces a resistor into the motor supply to drop the speed. Other method was simply to have a varispeed drive using a pair of offset plates and a rubber ball so that you could adjust the speed over a small range.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 01, 2015, 07:40:00 pm
content: This one doesn't seem to have any evidence of speed regulation ( or it's not working). There's a speed knob that adjusts a rheostat in the base.

author: Gyro
author_rank: Super Contributor
timestamp: November 01, 2015, 08:11:56 pm
content: Hey, that's nothing as a hazard - what about the resistive mains leads that used to be used as droppers for valve radios - Just the thing for coiling up on the carpet under the full length curtains!Edit: Come to think, they were probably stuffed with asbestos too!

author: tooki
author_rank: Super Contributor
timestamp: November 01, 2015, 11:10:20 pm
content: Quote from: Gyro on November 01, 2015, 08:11:56 pmOk wait, what?! Please tell me more about these, I'd never heard of them before now!

author: vk6zgo
author_rank: Super Contributor
timestamp: November 02, 2015, 04:35:17 am
content: Quote from: tooki on November 01, 2015, 11:10:20 pmVery rarely seen in Oz--our home grown industry almost always had transformers in radios used on 240v AC.There were some AC/DC "specials" because there were still places which had DC Mains supplies.but they were more like the few privately imported British AC/DC radios-------designed for 240v from the outset.We had 32v DC radios,too---my first Employer modified Ekco RM204 mantel radios so the RF & IF stages would work off 32V HT.I think they must have used a series string of 6.3 volt valves plus a resistor for the valve/tube heatersThe audio output was replaced by a couple of big Germanium power transistors.I only every saw two of the resistive lead things,& they were both "private imports" from the USA.Evidently the manufacturers would supply such leads if you were going to a 240v country.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 02, 2015, 05:03:11 am
content: Quote from: G7PSK on November 01, 2015, 05:09:38 pmHow did they deal with the arcing issues with HVDC? Or is that one of the reasons they stopped using it?

author: Gyro
author_rank: Super Contributor
timestamp: November 02, 2015, 10:50:42 am
content: QuoteI've browsed the web, and apart from mentions of them I haven't been able to find any pictures, so I've attached a photo of the relevant pages in my copy of "Radio, Television and Electrical Repairs" 1948, Third Edition 1956, Odhams Press (worth seeking out a copy if you're feeling nostalgic).There's a diagram of basic construction (resistance wire wound around an asbestos core!). They look as if they got quite complex, with straight through conductors and multiple taps (just like a traditional wirewound dropper). Not much descriptive text, apart from some sage advice not to shorten it! Enjoy.

author: Gyro
author_rank: Super Contributor
timestamp: November 02, 2015, 06:50:30 pm
content: Typical, I was just trawling the web and found a UK Vintage Radio thread with a pdf scan from the very same book! It also includes a bit more info from a few pages further on that I missed.The thread also includes a couple of photos...http://www.vintage-radio.net/forum/showthread.php?t=110595

author: Stray Electron
author_rank: Super Contributor
timestamp: November 02, 2015, 07:45:05 pm
content: Just combine with Nitro-Cellulose based film and you have the ingredients for en exciting and memorable evening!