20-11-2011, 10:19 PM
It's a Marconi CR.100 comms. receiver, WW2 vintage, and a receiver which was always very popular in the 1950 - 1970 period in Radio Amateur circles. They were manufactured in huge quantities and used by all the Armed Forces & various intelligence services. The Naval variant is known as a B28.
I've recently acquired one of these (motivation: pure nostalgia) and I'm in a bit of a quandry as to how to proceed. So I thought I'd ask here for others' opinions.
Basically, it's condition is as you would expect: its wiring is the original rubber-covered stuff and I can see that it is crumbling away in places. A few very-near short-circuits to chassis have been removed by my recent rewiring for this - but only in places where I can see. Now a lot of the under-chassis wiring in inaccessible, since it's behind tag-boards or buried deep in the crowded chassis. Moreover, I can see (that as is usual for these sets), there have been some extensive modifications: one involves the fitment of an extra 6SN7 which, upon analysis, circuit-wise, looks a bit weird. The mains transformer is not original and the PSU HT smoothing cap (a triple unit) has been replaced by a quadruple job. The rectifier reservoir is now 32 uF; it should be 8 uF. (Ouch! Said the rectifier! :omg Plus, there may well be other strange things in there that I haven't found yet.
Now the previous owner did say that he had "connected a bit of wire to the aerial socket and could get a few local stations"; well, maybe. But the issue is this: do I now embark on a detailed inspection / extensive fault-finding exercise, which will involve powering the unit up, and risking damage (if not on immediate switch-on via a variac or lamp limiter, but later on), and bit-by-bit replace items as I go along (incuding wiring), or do I just say "O.K., stop now. This item needs a complete stripdown, a total de-mod. to original and a wholesale scrub-up; a total re-build (usual replacement of Rs and Cs) plus a re-wire (usual coloured PVC wiring)", and simply just get on with it, on the basis that in the long run, this route will involve a lot less work (including post-rebuild fault-finding) and also eliminate the risks of serious burn-outs, etc.
The ultimate aim is not to do a full restoration as such, simply to tidy the receiver up, (electrically and mechanically), make it reliable, and restore its performance to spec. I'm fairly confident of my ability to meet my objective: I have the necessary experience & test equipment and a manual for it (and a very good manual it is, too) but there are two ways of making an initial approach - as outlined: namely, (1) a 'bit-by-bit' approach as I go along, or (2) a wholesale total dismantle and re-build ~ then switch it on.
So ~ which way do I jump? Your thoughts are appreciated.
Al.
I've recently acquired one of these (motivation: pure nostalgia) and I'm in a bit of a quandry as to how to proceed. So I thought I'd ask here for others' opinions.
Basically, it's condition is as you would expect: its wiring is the original rubber-covered stuff and I can see that it is crumbling away in places. A few very-near short-circuits to chassis have been removed by my recent rewiring for this - but only in places where I can see. Now a lot of the under-chassis wiring in inaccessible, since it's behind tag-boards or buried deep in the crowded chassis. Moreover, I can see (that as is usual for these sets), there have been some extensive modifications: one involves the fitment of an extra 6SN7 which, upon analysis, circuit-wise, looks a bit weird. The mains transformer is not original and the PSU HT smoothing cap (a triple unit) has been replaced by a quadruple job. The rectifier reservoir is now 32 uF; it should be 8 uF. (Ouch! Said the rectifier! :omg Plus, there may well be other strange things in there that I haven't found yet.
Now the previous owner did say that he had "connected a bit of wire to the aerial socket and could get a few local stations"; well, maybe. But the issue is this: do I now embark on a detailed inspection / extensive fault-finding exercise, which will involve powering the unit up, and risking damage (if not on immediate switch-on via a variac or lamp limiter, but later on), and bit-by-bit replace items as I go along (incuding wiring), or do I just say "O.K., stop now. This item needs a complete stripdown, a total de-mod. to original and a wholesale scrub-up; a total re-build (usual replacement of Rs and Cs) plus a re-wire (usual coloured PVC wiring)", and simply just get on with it, on the basis that in the long run, this route will involve a lot less work (including post-rebuild fault-finding) and also eliminate the risks of serious burn-outs, etc.
The ultimate aim is not to do a full restoration as such, simply to tidy the receiver up, (electrically and mechanically), make it reliable, and restore its performance to spec. I'm fairly confident of my ability to meet my objective: I have the necessary experience & test equipment and a manual for it (and a very good manual it is, too) but there are two ways of making an initial approach - as outlined: namely, (1) a 'bit-by-bit' approach as I go along, or (2) a wholesale total dismantle and re-build ~ then switch it on.
So ~ which way do I jump? Your thoughts are appreciated.
Al.