- September 16, 2018 at 9:30 pm #10421
Hillary ChesherCVRS Member
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
-HillarySeptember 18, 2018 at 2:08 am #10422
Sterling SpurrellCVRS Member
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 awhileSeptember 19, 2018 at 7:59 am #10427
Gary AlbachCVRS Member
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!
GarySeptember 20, 2018 at 3:31 am #10437
Steve DowForum Participant
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
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
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.
[email protected]September 20, 2018 at 6:54 pm #10438
Hillary ChesherCVRS Member
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.
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.September 21, 2018 at 9:49 am #10439
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.September 21, 2018 at 8:56 pm #10441
Steve DowForum Participant
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.
You must be logged in to reply to this topic.