A Marconi CR.100 dilemna.

[pwdrive]

Hello Al, for what it's worth try the bit by bit route if at all posssible, the method I always use is to get the receiver basically up and running by hook, crook or whatever means, that way I have a base to work from, then I usually start at the power supply end and work all the way up the front end, I usually replace all suspectibles associated with a given valve stage then do an ohms test (Avo) from ht +ve and any common screen divider network to ht -ve after rebuilding any particular stage before switching on to test the work just performed and moving on to the next stage. I suspect a total strip down would need plenty of notes and documentation and a good memory.
Sometimes with these old sets it can be a bit of a decision as to how far to go, the last one I did was a SX28 a couple of months ago, the wiring was ok but I replaced all the R's and C's except for the silver micas and the power supply electrolytics which were ok, I have two or three receivers that fully function with all their original components, these receivers have not seen a soldering iron since they left the factory so do I replace the waxies etc in them for future insurance or do I wait till they pack up...as the receivers work ok I have decided to leave them as is.
Good luck with the project which ever way you go.

Lawrence.

[Yorkie]

This is the dilemna of 'conservation' v 'restoration' - the older a set is, the more I think we should be inclined to keep it as original as possible - for example, by leaving resistors in place that are perhaps 50% out of spec if the receiver works, rather than perhaps changing those that are just 20%+ out of spec. But if we want it to perform as it was originally intended to when it was 'factory fresh' that involves more drastic work. As far as waxies are concerned, they're known to become leaky in the elctrical sense in which case they fail to do the job they're there to do, namely, to allow AC signals to pass while blocking DC voltage. When that happens, we can get DC where we don't want it - typically on the grid of the output valve, which can damage the valve, the output transformer and the mains transformer due to excess current being drawn. Even worse if the receiver has a mains energised speaker in which the spekaer field coil doubles as a smoothing choke, and consists of thousands of turns of fine gauge wire (not relevant to the CR100 of course). The is why 'That' capacitor (the one on the grid of the output valve) has gained such notoriety. It's such a cheap job to change waxy caps that it's hardly worth the risk. The same applies to Hunts 'mouldseal' caps - the ones in a sort of brown plastic encapsulation which is often crumbling or cracked. (Many Eddystone receivers used little oval red caps - notorious for becoming leaky too).

Others may not see things my way, but for me, the priorities I follow are:

1) Safety.
2) Performance and future reliabilty.
3) Originality.

I place originality last, because above all the set must be safe, and if it's intended to use it, it must peform as originally intended.

The last thing on my mind is originality, especially when it compromises safety and performance.

[Skywave]

Thank you Lawrence & David for your Posts immediately preceeding this.

Collating all the advice received here in this Thread, my approach on this has now been decided: in essence, what Lawrence (immediately above), and a few others, previously, have said. It will be the stage-by-stage method, replacing those components (including wiring) that are necessary to establish correct circuit operation. (Stages not under exam. will have their HT temporarily removed for obvious reasons). As far as a priority list of 'what, when & why' is concerned, I am in total agreement with David.

The stage is now set; I just need to find a quiet time to get stuck in. However, this will have to wait for a bit, since very soon I will be involved in a total bathroom overhaul and refit. That'll make a change from doing same to old valve radios, eh?

In the meantime, I remain receptive to comments and advice from anyone else. And "thank you" to all who have contributed so far.

Al. / Nov. 21, 2011 //
 

[pwdrive]

Hello Al, I have just finished some artwork (full scale) for the two logging scales on a CR300, I am not sure if they are the same for the CR100, the CR300 main logging scale runs though 360 decgrees (0 to 9 then 0) on each 180 degree section) the small one runs from 0 to 25 through 180 degrees, I have all the relevant dimensions etc to regenerate in a PC drawing program as well, if they are of any use in your restoration let me know and I can send them.
Good luck with the house diy (story of my life)

Lawrence.

[Skywave]

Thank you Lawrence. I'll check that out later on and then come back to you if those scales appear to be appropriate. I'm quite ignorant on the CR.300.

Al.

[Yorkie]

Hello Al, I have just finished some artwork (full scale) for the two logging scales on a CR300,
Lawrence.

A rare and useful talent Lawrence - what software did you use please?

I've furtled about with Paint, Adobe Photoshop, Autocad and what not, and am coming to the conclusion that I must be suffering from undiagnosed ADHD because I've never managed to get climb up the learning curve to a level at which I'm competent to create dials from scratch. The best I can do is to tidy up scans, and I marvel at the accomplishments of some restorers, most of whom, to my chagrin, aren't professionally engaged in CAD but are self-taught.

I am not worthy! :-/

[pwdrive]

"Don't panic Mr Mainwaring" Hello Dave, it wasn't easy for me either, I used to do all the paint/graphics stuff years ago in the days of windows 95 when helping our girls to do there homework!! so it's a re learn curve for me as well.
The software I used is "Inkscape" free download on the web and is quite easy to use although I am still finding my way round it, I will try and upload the artwork for the two scales I have done to this site if I can figure out how to do it.

Lawrence.

[Yorkie]

"Don't panic Mr Mainwaring" Hello Dave, it wasn't easy for me either, I used to do all the paint/graphics stuff years ago in the days of windows 95 when helping our girls to do there homework!! so it's a re learn curve for me as well.
The software I used is "Inkscape" free download on the web and is quite easy to use although I am still finding my way round it, I will try and upload the artwork for the two scales I have done to this site if I can figure out how to do it.

Lawrence.

Free eh? I like the sound of that Lawrence!!

I see that you've managed to upload the scales to the forum in another post, and very good they look too!