|
Post by Peter Walsham on Jun 29, 2021 11:09:46 GMT 12
Good morning Steve
Comment regarding the mains flex 'corrosion'.
With regards to the green 'corrosion' found on many mains cords. I have come across this many times over the years. It became a real issue in fixed wiring situations in houses, rest homes, commercial & industrial buildings, and many other places as well (often seen as green goo leaking out of light switches & power points, and often even 'dripping' down walls. A study was done many years ago (when I was working as an electrician) and I read a comprehensive report about this at the time, and the conclusion was that the green 'goo' was the plasticiser (as PVC is hard & brittle when it's made, a plasticiser is added to the PVC mix so cables & flexes can be made to be flexible) used in the PVC cables which was reacting with the copper wires (PVC, itself, contains Chlorine, which was what was giving the 'goo' its green colour, but I'm not sure if the plasticiser contained Chlorine as well). I assume a fixed cable had less of the plasticiser than a flexible cord, as a fixed cable didn't really move, once it had been installed. . It was stated (at the time) that the green 'goo' wasn't harmful (it didn't appear to degrade the performance of the copper wires, or the insulation resistance of the cables), however it did tend to make cables/flexes a bit more brittle. Nor is the goo toxic. The reaction between the plasticiser and the copper appeared to change the plasticiser in to a rather viscous 'liquid' (which appears in the form of this green 'goo'. Apart from the cosmetic problem of the goo, the problem cables were considered as still being 'serviceable' and did not require replacement. As far as flexes are concerned, I have frequently seen this on the flexes that preceded the 'tru-rip' type of flex. The green goo seems to be more of a problem on brown PVC flexes than other colours (grey & white) (maybe the brown PVC needed more plasticiser?). As for corrosion of the copper, I have not come across this at all. The green goo is rather unpleasant to 'work' with, and I replace any cords that I see having signs of the green goo anyway.
Hope this is helpful?
Peter W
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on Jun 29, 2021 19:59:14 GMT 12
Hi Steve I've got a cabinet off a courior radio I'm working on and I noted that you use Briwax. Excuse my ignorance but is that a wax or oil as with a quick look online I see Briwax oil Cheers Wayne
|
|
pete
New Member
Posts: 28
|
Post by pete on Jun 30, 2021 9:26:26 GMT 12
Steve
Sadly, there is no progress to be reported.
My wife will not allow me to work on the dining table.
I may have to spend a few days clearing stuff out of the garage to make space. (It has been months since last my personal vehicle has seen the inside of the garage either.)
Will let you know once I get going again.
Regards. Pieter
|
|
Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jun 30, 2021 10:18:07 GMT 12
Good morning Steve Comment regarding the mains flex 'corrosion'. With regards to the green 'corrosion' found on many mains cords. I have come across this many times over the years. It became a real issue in fixed wiring situations in houses, rest homes, commercial & industrial buildings, and many other places as well (often seen as green goo leaking out of light switches & power points, and often even 'dripping' down walls. A study was done many years ago (when I was working as an electrician) and I read a comprehensive report about this at the time, and the conclusion was that the green 'goo' was the plasticiser (as PVC is hard & brittle when it's made, a plasticiser is added to the PVC mix so cables & flexes can be made to be flexible) used in the PVC cables which was reacting with the copper wires (PVC, itself, contains Chlorine, which was what was giving the 'goo' its green colour, but I'm not sure if the plasticiser contained Chlorine as well). I assume a fixed cable had less of the plasticiser than a flexible cord, as a fixed cable didn't really move, once it had been installed. . It was stated (at the time) that the green 'goo' wasn't harmful (it didn't appear to degrade the performance of the copper wires, or the insulation resistance of the cables), however it did tend to make cables/flexes a bit more brittle. Nor is the goo toxic. The reaction between the plasticiser and the copper appeared to change the plasticiser in to a rather viscous 'liquid' (which appears in the form of this green 'goo'. Apart from the cosmetic problem of the goo, the problem cables were considered as still being 'serviceable' and did not require replacement. As far as flexes are concerned, I have frequently seen this on the flexes that preceded the 'tru-rip' type of flex. The green goo seems to be more of a problem on brown PVC flexes than other colours (grey & white) (maybe the brown PVC needed more plasticiser?). As for corrosion of the copper, I have not come across this at all. The green goo is rather unpleasant to 'work' with, and I replace any cords that I see having signs of the green goo anyway. Hope this is helpful? Peter W Hi Peter, thank you for that info - I am indeed referring to the green slime that this cord tends to exude. Your explanation of how it is formed has answered a question I've wondered about for years...
And Pete - your wife sounds sensible... mine lets me pull radios apart on our table - and its a mess. Currently its covered with parts of 3 different radios and can not be used for anything else. My wife should learn from yours
|
|
pete
New Member
Posts: 28
|
Post by pete on Jul 1, 2021 13:53:55 GMT 12
Steve I have started work on the items I am able to handle at the moment. I have cleaned and oiled the cabinet. I concentrated on the inside and bottom of the cabinet for now. The timber was incredibly dry (and most likely rather brittle). The cabinet "drank" almost half a cup of oil yesterday and may consume a little bit more today. (There is a bit of sun out today - better make use of it.) Some of the boards on the bottom have gone a bit crook over the years (some shrinkage and warping) but all in all the cabinet looks great and I do not foresee any problems. My only concern with the cabinet is that I may have robbed it of its "character". Valve radios are meant to smell a bit dusty when they warm up, do they not ? I buffed the speaker housing and have applied a coat of clear varnish. The metal was showing signs of spotted rusting. I have dealt with that. The speaker seems to be in fine nick. The grill cloth is a bit tired but not torn or perished. I am going to leave it as is. It was glued to the grill board. More later. Pete
|
|
pete
New Member
Posts: 28
|
Post by pete on Jul 1, 2021 14:34:49 GMT 12
Steve I did the checks on the mains power cord after lunch. The connections and cord seem OK. I now see what you mean with the "hidden earth wire" contained inside the cord. The mains power feed seems safe and usable. I may want to replace the cord (and maybe even the plug) at a later stage. It is not critical at this point and I assume that all tests can be done with the old cord and plug. Questions: Can a dim bulb test be performed at this stage ? If so what do I have to look out for ? (I have watched the video and have a good idea about what is meant to happen if the unit actually fires up.) I take it that the mains power merely feeds a transformer in this type of radio. Can I assume that the radio set thus does not care about polarity ? (By the way - I now have seen three ways of designating the live wire on mains appliances. It is either shown as A (active ?), L (line ?) or P (power ?) as on the photo shown. Can you enlighten me on the failure modes of a valve ? What does one look like if it is OK ? ? What does one look like if it is not OK ? What does it look like if it is working ? (I remember a faint glow emanating from some (or all ?) of the valves on dad's old radio when it was working. Do valves fail catastrophically or do they simply fade away to a point where they do not work properly any more ? Cheers Pete
|
|
Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jul 3, 2021 0:26:36 GMT 12
Yep - power it up And you are correct, polarity is important for safety but not for operation in your set. P is for Phase (the modern designations are Phase, Neutral and Earth). Active or Live are also used but I'll let a sparky or someone more in the know explain why (because I don't know the origins/etymology of the different terms, or if there is a subtle difference in each). Valves fail in all kinds of ways - I recently had one 'blue plate' on me, which is where the valve glows intense purple, they also can just fade away as the material on the cathode is depleted, or the heather can fail... there is no one specific failure mode for them. But yep, power it up
|
|
pete
New Member
Posts: 28
|
Post by pete on Jul 4, 2021 13:15:15 GMT 12
Steve Nice winter's day so I decided I will take the testing rig and radio outside. I fired up the radio through the dim bulb tester. No smoke, no fire, no crackling noises on the speaker. The dim bulb tester behaved like you predicted in the video. I did not however have an idea as to the current the set was drawing. I do not have fancy testing equipment. I did however a few years ago buy a device which helps analyse power consumption. It allows you to measure the power consumption of devices plugged into your mains power supply. It will measure KWh, watts or amps. It also shows the supply voltage. I have decided to put it to use as part of my dim bulb testing set-up. See set-up in photo. Mains power is fed through the amp-watt meter, goes through the dim bulb tester and then feeds the radio. There are two switches on my dim bulb tester. This allows me to switch between zero load (short circuited plug seen on photo [please do not EVER let my sparky see this photo ]) and the load seen through the radio, or whatever is plugged into the other socket. At zero load my measuring device shows 42 watts being consumed. (Little lower that I would have expected - it is a 60 watt globe) When the radio is switched into the circuit (bulb and radio now both in circuit), then after about half a minute I measure 36 watts. I am not quite sure what that tells me about the consumption by the radio itself. (It has been 40 years since last I looked at the formulae associated with electrical relationships !) If not persuaded otherwise, I think I'll fire up the radio without the benefit of the dim bulb tester. I'll then be able to measure the current being drawn by the radio in its current state. (Does knowing this help you guys any ?) Regards. Pieter
|
|
Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jul 4, 2021 17:07:09 GMT 12
Hi Pete - if that plug is what I think it is then please destroy or undo it - put a switch on the board to bypass the bulb - you don't need a system to short the feed, but it is handy to have one that shorts the bulb out so you can feed the radio via the bulb, or directly.
Knowing the current is mostly useless - the difference in mains current between good and not so good capacitors inside may not be significant at the primary side of the transformer. You should have within cooee of 50W draw without the bulb (its on the plate on the back of most radios), but I generally never bother to measure or note this unless I think something is wrong (in which case the bulb will tell me).
Wire a switch across the bulb, close the switch, measure the power usage... it should be about 50W
Even though you've now checked it, don't run it for too long (more than a few minutes at a time) until the main power supply caps have been replaced. And let it rest between runs. If the main electro can is on its way out they can slowly heat up and fail (with some gusto) as they get warmer. And never leave it powered on alone until its been repaired.
Cheers, Steve
|
|
Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jul 4, 2021 17:11:07 GMT 12
|
|
pete
New Member
Posts: 28
|
Post by pete on Jul 4, 2021 17:39:08 GMT 12
Report on Sunday June 4th progress.
Steve
I refer to an earlier post (mine) today.
I did not fire up the radio without the dim bulb tester in line. (Please advise on the suitability of doing so at this stage.)
I removed the tuning dial window so it can be inspected and cleaned. No problems there. Doing so allows me more un-obstructed access to the top of the chassis and less chance of breaking things (by tilting and fiddling about with the chassis) as well.
I refer to some of your earlier posts.
Jun 27, 2021 at 11:04pm
You will need to replace the power supply capacitors most likely (unless they have been done recently). There are 2 x 40uF (said: micro-farad) 450V Electrolytic Capacitors (C1 & C2) on the schematic - and there is also a 25uF cap, C3 which is probably in the same can and will also need replaced - 25uF 50V is what I usually use here. This can containing all these caps on your radio is beside the power transformer and branded 'Elna' - and it looks like 47uF 350V is used instead. You should have no trouble finding 47uF 400V or 450V capacitors to replace these though. Its ok to use higher voltage ratings.
Once done there, all the tubular paper-foil capacitors (often called wax caps or waxies as they are dipped in wax to protect them from moisture ingress) will need to be replaced - they are likely all crook by now.
Jun 28, 2021 at 5:27pm
I think the next step will be to draw out the power supply section and make sure you understand how it is configured before attempting to replace any parts. There are several ways to replace the electrolytics from just whacking them in, to fully restuffing the existing can with new parts. I tend to take a middle-ground approach and use tag-strip to mount new caps and then fit that near the existing can underneath.
Questions:
Can anything be gained (or lost ?) by firing up the unit with no dim bulb tester in line to check the current being drawn ? How do I go about analyzing the power supply ? Can the live voltages on the terminals of the power transformer be measured out without doing any de-soldering ? Will doing so teach us anything ?
I guess that the next step will be to fiddle about with the can next to the transformer. How do I get access to it ? It seems to be attached to the chassis by lugs which were twisted to lock it in place. Do I need to de-solder the wires leading to it and then remove the can ? I have no idea what I might find inside. Guess I will learn as I go.
Some of the valves have a metal shroud around their body. What is the function of these ?
Is it worth the while to start hunting down replacements for all of the valves in this radio ?
Where do I most easily find the capacitors needed for replacement of the components in the can (and for other components I will need in future) ? (I every so often drive into Timaru and have a good working relationship with the guy at the Jaycar dealership there. My other option is get stuff by connecting with a supplier on-line. My least preferred option (but not out of the question) is to drive through to Christchurch if/when I require components.
Other issues:
Thus far I have produced incriminating stuff (as far as my sparky might be concerned).
I am about to start producing incriminating stuff (as far as my wife is concerned).
How much do valves cost ?
Cheers for now. Pete
|
|
pete
New Member
Posts: 28
|
Post by pete on Jul 4, 2021 17:47:02 GMT 12
Steve
I read your reply from a few minutes ago just now. It seems we were working on posts at the same time ! I have to take a break for tea now. I may check in on the thread one more time today (if my wife allows it !) Pete
|
|
Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jul 4, 2021 19:07:38 GMT 12
I did not fire up the radio without the dim bulb tester in line. (Please advise on the suitability of doing so at this stage.) Yep - do it, refer to my previous post about not running it too long though Questions: Can anything be gained (or lost ?) by firing up the unit with no dim bulb tester in line to check the current being drawn ? How do I go about analyzing the power supply ? Can the live voltages on the terminals of the power transformer be measured out without doing any de-soldering ? Will doing so teach us anything ? Everything you do will teach you something - it may not be useful, or it may not be useful *right now*... but the more things you try the more things you learn... The best thing to do here is to understand how the power supply works. I could explain it - Uncle Doug already has though - so watch this: www.youtube.com/watch?v=x5SSKX74DKgEffectively the power supply capacitors smooth the rectified AC into clean DC. When they start to fail, they tend to fail short cct... which means they start to dump their voltage to ground, which causes heat, which causes more failure... and so on. This act of dumping voltage to ground causes more current to be drawn in the secondary windings of the transformer, which is more heat, which causes the insulation in those windings to fail, and short together... which ends catastrophically. And while the transformer in your set is not made completely from unobtainium - there is no point putting it under stress for no reason... and this is why I don't just replace the capacitors I can get away with - I always replace ALL old caps. David Tipton talks about replacing the electrolytic caps in a radio here: youtu.be/VMLIqfq25vU?t=715 and goes through the process of using tag strip to mount new caps. That radio is an older one, and the electrolytics are separate cans for each one - yours has 3 or 4 in one can, but the idea is the same. He does another one where he brutally cores and then restuffs the can here: youtu.be/R1EhFlJru2w?t=952 - I also restuff one here: youtu.be/c3rzT6bwnHc?t=1376 but I do it in a slightly more complicated way. And in terms of the voltages - yes, you can test the voltages that come out of the transformer. You'll probably have 6.3V (give or take) to the rectifier heater, another 6.3V to the heaters of all the other valves and the dial lights (in parallel), and around 350-0-350V HT - all of these are AC voltages. If you look carefully at your transformer it has markings indicating which is which. I guess that the next step will be to fiddle about with the can next to the transformer. How do I get access to it ? It seems to be attached to the chassis by lugs which were twisted to lock it in place. Do I need to de-solder the wires leading to it and then remove the can ? I have no idea what I might find inside. Guess I will learn as I go. See above Some of the valves have a metal shroud around their body. What is the function of these ? That is to stop any interference from one part of the circuit (or external sources) affecting the small signals in a valve - removing the shields can sometimes have no effect, if they've been fitted 'just in case' - or it can cause the circuit to go unstable and start motorboating, howling or screeching. Is it worth the while to start hunting down replacements for all of the valves in this radio ? Almost certainly not. I wouldn't replace any of them unless you know they need replacing. And they most likely don't. Its a common misconception that old radios that don't go probably just need a new valve. This is typically (but not always) wrong. Valves last a long time. Its certainly worth testing them, if you can, but I'd just leave them until you can categorically say one of them needs to be replaced. And replacing good valves just takes one more spare out of the pool of spare valves available. That probably doesn't matter today - but 50 years from now it might. Where do I most easily find the capacitors needed for replacement of the components in the can (and for other components I will need in future) ? (I every so often drive into Timaru and have a good working relationship with the guy at the Jaycar dealership there. My other option is get stuff by connecting with a supplier on-line. My least preferred option (but not out of the question) is to drive through to Christchurch if/when I require components. You can get capacitors through the NZVRS at good prices. Membership has its privileges (Failing all else, I also have decent stock levels in my workshop) Other issues: Thus far I have produced incriminating stuff (as far as my sparky might be concerned). Yes, see my earlier comment on that... it really needs to be dismantled I am about to start producing incriminating stuff (as far as my wife is concerned). You're brave... How much do valves cost ? Cheap, typically, for the ones in your set - maybe between $5 and $20 per valve - I wouldn't pay any more than that. I have quite a few of all the common types in boxes here for when I need them, but if I don't have it then I email my guy. Twenty_B on Trade Me - Gary. A very nice guy that has pretty much always been able to find me what I have needed at reasonable prices. So - next steps: 1. Power it up for a couple of minutes without the bulb just to prove its working. You might need a decent length aerial down there to get stations well, I'm not sure what you've got available down there. 2. Replace the power supply caps, then re-test it. Always do small amounts of work then re-test, it will help isolate issues if any occur while you're working on it. You could certainly check the current draw with old caps and new just to see if there is a difference. Technically there should be, and I'd actually be interested to know what (if) it was. Cheers, Steve
|
|
pete
New Member
Posts: 28
|
Post by pete on Jul 5, 2021 0:08:12 GMT 12
Steve
Thanks once again for all of the feed-back and suggestions. It seems as if I need to check a few more internet sources and then do a few more experiments tomorrow. I can but hope that I will make some decent progress. Unfortunately the radio project is not the only one currently "running" (according to my wife "ruining") my life ! I am at the same building cigar box guitars for my grandchildren, experimenting with low-output guitar amplifiers and affording running repairs to the equipment on our LSB. It keeps me out of trouble, I guess, but it also creates a terrible mess and leaves me with preciously little work space.
Regards. Pete.
|
|
Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jul 5, 2021 11:11:33 GMT 12
Hi Pete - I totally understand, as I too have LSB maintenance and repairs (not to mention the animals) getting in the way of my radio antics... Vintage Radio restoration is an exercise in patience... there is no rush.
Cheers, Steve
|
|