Advice on rewiring

[Hillary Chesher]

Hello! This is my first post on this forum. I am very new at working with radios (this is my second one) and still quite new at working with electronics. I am looking for a bit of guidance on how much re-wiring my new radio needs.

I recently acquired a Marconi 148 farm radio and plan to restore it. I haven’t started yet but I’m trying to plan out exactly what I want to do with the wiring. The plastic insulation on the battery leads and the speaker leads is in bad shape with large chunks missing so I plan to replace that. For the wiring under the chassis: the plastic (is it even plastic?) insulation on the wires is extremely dry and cracked. There aren’t any chunks of insulation missing but I’m concerned about the danger of a short in the future. The first radio I worked on had dry, cracked, but not too sketchy looking insulation and shorted the first time I powered it… so I’m trying to learn my lesson.

What I am wondering about is how much of the internal wiring actually needs replacing. I have been reading around on the internet and have seen cautions about the importance of lead dressing and the harm that can be caused by wiring things willy nilly. I would like the radio to work but I also don’t want it to be a perpetual fire hazard. I just don’t think I have enough knowledge to know when rewiring is actually needed or if I’m just making trouble for myself and causing more harm to the poor thing. It’s going to be cleaned and re-capped when I get around to it. I just want to get my ducks in a row (as much as possible) before starting any work on it.

This is the back of the set the day I brought it home. The battery leads and speaker wires are going to be replaced.

This is the underside of the chassis. You can’t see it but there are actually a lot of cracks on the insulation. It is at risk of shorting when I power it on? Is it worth replacing?

Any guidance is appreciated

-Hillary

[Sterling Spurrell]

From my past experience you should replace any wire that looks bad has it will become a problem either now in your process of getting the radio working or later after you play it for awhile

[Gary Albach]

Hi Hillary, and welcome to the forums. There is a lot of experience out there with our members and many of them are willing to share their knowledge to help us all.
I agree with Sterling that you should replace all wiring that looks suspicious. You say that you will be cleaning and recapping the set, so that would be the time to replace the bad wires as well. When you are replacing the capacitors and out-of-tolerance resistors, just jiggle the wiring and you will easily tell if it needs replacement. The insulation is probably rubber (not plastic) and if it’s bad it will crumble when you grip it in your pliers. (It’s interesting that some colors of this old insulation seem to stand up better than others. Some colors crumble, others turn soft and mushy.) Dont be too worried about getting the lead dress exactly perfect when you replace the old wires – just put the new ones as close to where the old ones were as you can. You have taken good pictures to help you here.

Keep us in the loop as you go along and post some pictures when you’re done!

Gary

[Steve Dow]

It is a battery radio, so fire hazard is minimal. The underside looks clean. You might take note
of the white coating on the inside of the radio and treat it with care until you know exactly what it
composed of.

If you obtain a power supply to operate the radio, check that it
CSA approved as this will be your fire hazard protection.

This radio needs an antenna. If outdoors, lightning protection
is needed.

With the battery cable rewiring, extreme attention is needed because the tubes
can be easily burned out if the A and B circuits are crossed.

I assume you have the RCC (Radio College of Canada) service data.

If you do want the data from the Marconi service manual, I have it
and can email pages gratis.

I am looking at models 148/149 pages as I type this.

You radio has also a single short wave band, the 31 meter band.

Steve Dow

[Hillary Chesher]

Hi guys!

Thanks for the feedback/advice. I wiggled a few of the wires with pliers while cleaning around under there today and, yup, the rubber was crumbling. So I’ll swap out most of it and see how it goes!

Steve, thanks for the information on fire hazard protection. I don’t know what I plan to do for an antenna yet– I’m moving in such small baby steps that even turning it on seems worlds away. Thanks for the warning about the battery cable wiring. I’m hoping I’ll have a sure idea of which is which by the time I’m done swapping things out. If not, I’ll definitely ask before hooking it up. I don’t have the RCC service data but I think I got the Marconi ones from radiomuseum.org. I have three pages of schematic for it. However, I don’t know if that’s complete.

Thanks again for the help. It’ll take me a while to get through this but I’ll post back as I hit roadblocks.

-Hillary

EDIT: I just noticed that in my original post I said it was a Marconi 148…… it’s a 147. Not that it makes a difference to any of the above.

[phil]

if solder joints are hard to access you can slip heat shrink over the wire. some wire was rubber and certain radios have a lot of it. the cloth covered stuff stands up better. If you like using the heat shrink it comes in colors and you can smoke it a bit with a lighter to make it look not so bright. In the old days they didn’t use heat shrink but rather something called spaghetti. It doesn’t shrink, just slips over the wire and you can get new old stock stuff if you look hard.
that one isn’t too crowded some of the rogers sets and others have a lot of old rubber wire and it can be a time consuming affair.
to not get confused, take a couple of bits of colored insulation and stick them over any wires you clip. that way if you are drawn away by the phone or somethign and go back you remember where they went. taking pics helps too.
as stated depending on color it can turn to mush or peanut brittle.

its a bit overkill but you can get meter lead wire. it is very soft ruber but also good quality wire, better than you need but sometimes I like it because it seems ot fit in well and easily available.

insulation has ratings so the wire insulation should really match or be of higher grade than the voltage it sees. most old radios didn’t use plastic wire. at least until the 50’s or so.. I don’t use that some do, be careful of possible heat sources that might melt plastic if you use it. soldering iron will melt it of course.
you can also get a covering , found in stoves. it is heat resistant and not shrinkable, usually white. its ok to add that if protect if you are near a point that might be a bit warm and you just want a little further protection. If you can, try to keep the colors as they are sometimes referred to by color.

some like to re-stuff the old paper shells and keep all the wiring looking original others feel it cant’ be seen anyway, Your choice how far you take this, might depend on the value or age of the set or how fussy you want to be.

[Steve Dow]

The wire in your radio is type VSR 32 or VSR 64 , called super aging rubber.
Rated at 300 and 600 volts and temp of 50 degrees C.

[Don Henschel]

That is a nice looking set and I also had the same concerns with my Philco 444 from 1936 about the wiring. A few days ago I was poking around under the chassis to determine what capacitors I needed to order and looked and poked at the wiring. It is all cotton covered and all the wiring below is very flexible with no signs of rot or getting hard so it will remain. The speaker wiring is in fair condition with slight fading and if I find “politically correct” cotton covered wire it might be replaced. The infamous capacitor blocks are the chalange but other than that it is something to work with.
The silk cloth is damaged and impossible to find so I gave up and subbed a semi glossy curtain material that looks period correct and has the same sheen as the original just a bit fancier. Yes I’m also one of those “stuffers” as well as I think those yellow fellows staring back make me cringe.

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[phil]

a couple of wire sources :

https://www.tubesandmore.com/products/wire-20-awg-stranded-core-lacquered-cloth-cover-600v

and

Cloth-Covered Wire

[Don Henschel]

Fantastic and thanks for the link because my “Fanger” uses the cotton as well and even my 1950 Mercury has full cotton or should I say rubber with cotton but under the hood the heat has made some of it start to separate but at least complete exact reproduction harnesses are available. I see the older 30’s sets for sale on eeevilPay with vinyl wire and those yellow fellows staring out at you kind of like sunny side up eggs.

[phil]

I use a double boiler which consists of a hot plate , with a pot of water and a soup can with wax in it. as I replace the paper caps I let them sit in the molten wax a minute, then just use a pencil to push out the guts from the paper tube.
and then I put the new caps inside. usually I splice on thicker wire to mimic the old ones solder the splice and hide the splice inside. . lots of new caps have thinner wire. I stuff a little kleenex in the end of the tubes hiding the new cap and put a bit of hot melt glue in the ends to seal it up. when done that I return them to my molten wax for a dip.. a lot of those old caps have beeswax so I just keep the same wax going to let it discolor a little and to let it accumulate some of the beeswax.

I like doing it that way as it preserves the labels. I’ve even found I can drill out the old black beauties and do the the same way. someone might come along and clip them all out at some point but it’s worked for me. If you want to be so ahem..-retentive , you can too.. 😉 of course if you do a really perfect job you can revel in the fact that no one notices your work, as is the case with most good restoration. Especially here because they are usually hidden below chassis anyway.

if you are having fun it’s ok, Some like to stretch out the fun a little longer 😉

if you ever go to work on electric motors, sometimes you’ll see the spaghetti used there to cover up the wires from the field windings to the little connection box. i found some on ebay a long time go and still have most of it. You can usually reuse it and sometimes its handy to have some of the thinner stuff to cover wires from capacitors and stuff.. or maybe wires that do show like to grid caps on tubes. as a last resort you might ask if you have a motor repair shop. maybe they buy new spagetti. It might be better under heat and vibration.. it looks a bit more original than heat shrink.
some of the heat shrink has sort of like glue inside it. there are different types and colors.

a source of rubber coated wire is from AC wire ( cabtire) the black heavy rubber coated cord used in commercial electrical wires. the most common is white red black and green. the red is usually a bit more pink than red. I think its OK but it isn’t really the most durable insulation. sometimes if you cut just a few inches you can pull the old wires out of the rubber sheathing and then stick your solid wire inside it. an example is to cover an inch of wire between a cap and where it is connected. if you do this ,you can be sure the wire now has no real CSA rating since you messed with it so use caution and common sense of course. the meter lead wire has a good resistance I think 600 volts and the wire inside is many strands of soft coppper so it will work in pretty much any radio application with perhaps a wider safety margin. I dont; like plastic wire , its too easy to melt it accidentally with a solder gun though in reality its probably quite safe. it kind of glares at your work like the yellow caps and jelly beans do. In most cases probably safe enough just not my favorite so far as original looks.
a lot of the parts in old radios were way overkill and probably most of the wire is ridiculously huge when you consider the amps it is carrying but there isn’t enough used to consider trying to work though ohms law and compare the load and wire size to save wire cost. , Instead we use wire and insulation that is way too heavy so that in some instances where the insulation rating is important , it is good enough. I think once we’ve made any changes to the wiring we have also required our work to be re certified by CSA , like if you were to try to use an old radio in a business or commercial setting they may want it re certified to have a valid CSA stamp and that would be interesting 😉 Care homes usually have a requirement that they need to inspect any electrical devices that you take to residents. I’ve often wondered what they would think of an old radio that was restored.

Phil

• This reply was modified 6 years, 2 months ago by phil.
• This reply was modified 6 years, 2 months ago by phil.

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