|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
16th Oct 2017, 1:20 pm | #1 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Electrolytic caps never fail to disappoint
I restored my 1939 Andrea KTE-5 TV set perhaps 15 years ago. I tried at the time to make it period correct. The waxies were stuffed with modern caps and to seal them in I poured polyester resin into each end on separate days, when it sets it looks almost like a wax end. I used matching fabric covered wire. When I got the set it was just a rusted shell, with a grossly damaged tuner section.The set, since restoration, had only been switched on a few times over the years for demo purposes.
I was doing a bit of tidying up (of all things just after I fixed a faulty air con unit that had an open circuit electro in it) and I noticed a spot of corrosion on the KTE-5 chassis. Closer inspection showed that one of the dual 20uF 450V electrolytic caps had sprung a leak and damaged the chassis nearby, the capacitor still tested ok. What a disappointment . I'm beginning to think, as I did in my HMV904, that I should have replaced these with non electrolytics so that I never have this sort of problem again. I'm really fed up with faulty electrolytics, the trouble they cause never stops. Not a wonder I got so excited when my Conrac video monitor turned out to have none in it. (On the underside chassis photo, out of interest I put a red ring around an odd component. It is a miniature zinc-carbon cell that Andrea used as a grid bias battery for one audio stage) see attached photos. |
16th Oct 2017, 1:52 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
|
Re: Electrolytic caps never fail to dissapoint
Are those wax caps all original? If so, I'm surprised they're not leaky. Maybe it's something to do with the Queensland climate.
|
16th Oct 2017, 2:14 pm | #3 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to dissapoint
Only the outer cardboard casings are original, from the caps that came in the set, a few were missing and you can see where the yellow poly caps are. As noted I replaced the innards of all these waxies with modern poly caps and sealed the ends with polyester resin. To do this I wrapped fibreglass insulating tape around the poly cap, until it was a push fit and a seal in the wax cardboard tube. Then I could pour the polyester resin into the ends (on separate days) without it leaking past the inserted capacitor.
To make the old outer wax paper cap tubes clean up well, I found if I heated them in an oven, just till the old dirty wax melted and then wiped them down with a paper napkin it cleaned them up really well. Also heating them made it easy to pull the old capacitors out of the tube. (The reproduction fabric covered wire I used to rewire the set came from Antique Electronics in the USA). |
16th Oct 2017, 2:26 pm | #4 | |
Octode
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
|
Re: Electrolytic caps never fail to dissapoint
Quote:
Quote: "The waxies were stuffed with modern caps and to seal them in I poured polyester resin into each end on separate days." Argus, that really is quite beautiful: I could look at that under chassis view for hours!! Maybe electrolytic technology hasn't improved as much as we thought. After all they are still going to use chemicals so the possibility for leakage will always exist. All the best Nick |
|
16th Oct 2017, 2:30 pm | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
|
Re: Electrolytic caps never fail to dissapoint
Certainly a very impressive job.
|
16th Oct 2017, 2:33 pm | #6 |
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
|
Re: Electrolytic caps never fail to dissapoint
Oh Argus, how could you not wrap those few yellow perils in brown paper!
A lovely job, a credit to you. Perhaps the old, reformed, electrolytics may not have leaked? |
16th Oct 2017, 2:38 pm | #7 |
Guest
Posts: n/a
|
Re: Electrolytic caps never fail to dissapoint
Only 78 years of life, how terrible! Super job too.
|
16th Oct 2017, 2:43 pm | #8 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
|
Re: Electrolytic caps never fail to dissapoint
Indeed. Considering one blew up in my daughter's radio she got when she was two and now she's four, I think you did ok out of that electrolytic capacitor!
|
17th Oct 2017, 1:03 am | #9 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to dissapoint
Quote:
I think the original electros in this set were the genuine tall wet electrolytic type and usually all the liquid leaks out of these too! |
|
17th Oct 2017, 9:10 am | #10 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to disappoint
I'm working on an idea to get rid of this electroyltic capacitor nightmare for good for TV & radio restorations, if it works out I'll add it to this post.
I have attached some photos of the "Tuner" in this set. Being a kit set, the tuner part with the two coils and local oscillator and mixer of it was pre-fabricated by the factory. I've attached a photo from the manual. It had unique gigantic piston ceramic trimmers with 3/16" rods looking like miniature nuclear reactor control rods. All of the piston trimmers were missing and the tuner section was "butchered" with loose hanging coils and one original coil missing, photo attached. I managed to track down these piston trimmers, a couple from the USA and the rest from, as it turned out, a particular brand of Australian radio, but I had to cut the length of some down. I made a reproduction coil to replace the missing one. The design of the mixer is interesting, based on an 1852 pentode and the L/O is a 6J5, coupled to the 1852 grid coil with inductive link coupling. (these photos are scans of ones taken with a 35mm film camera!) Photo of the restored tuner section attached. I went to a ceramic rotary switch, its only two channels. |
17th Oct 2017, 10:21 am | #11 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
|
Re: Electrolytic caps never fail to disappoint
Those piston trimmers look identical to the type used in the RCA AR88 used in large numbers by various Allied forces during WW2 and possibly various other contemporary equipment- the UK military seemed to have a near-kleptomaniac attitude to stores holding and the AR88 was used by them long after the war, so these trimmers do pitch up from time to time as NOS or good condition used in the accustomed places.
Electrolytics are a compromise solution to a particular requirement I agree- but even in expensive professional kit, there seems to be a bit of a Jekyll-and-Hyde attitude among designers as to their use. That's a lovely piece of restoration there! |
17th Oct 2017, 12:39 pm | #12 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
|
Re: Electrolytic caps never fail to disappoint
Quote:
Maybe apotheesaurigoomaniac would be closer? (Made up word from Greek for hoarding)!
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
|
17th Oct 2017, 1:27 pm | #13 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,185
|
Re: Electrolytic caps never fail to disappoint
I understand the leaking electrolytic was restuffed? Or is it a modern can one? Depending on the cap that was used in the restuffing and on the way it was restuffed, leakage could be 'normal', but the right cap fitted the right way would probably only start to leak in 50 years or so.
|
17th Oct 2017, 1:45 pm | #14 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to disappoint
No, it was not re-stuffed. It was a "new electrolytic" NOS that was probably one or two years old when I fitted it. So it is an electrolytic, with minimal to no use (power on time) that leaked after about 15 to 17 years of age.
|
17th Oct 2017, 1:53 pm | #15 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to disappoint
Thanks, I wondered where these originally came from, maybe RCA made them. They are actually pretty nice and easy to adjust and lock. But they look like an expensive part compared to many more cheaply made looking trimmer caps.
|
17th Oct 2017, 2:16 pm | #16 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
|
Re: Electrolytic caps never fail to disappoint
Thinking of the post-war "one dollar for ten" Lend-Lease settlement and the perspective of the US tax-payer towards the UK's wholesale acquisition of of US equipment.... Though a great deal of this kit would admittedly have been deep-sixed or turned into ingots otherwise, and the US was keen on keeping friends in the nascent Cold War.
|
17th Oct 2017, 2:25 pm | #17 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
|
Re: Electrolytic caps never fail to disappoint
They are nice components- but compared to three other contemporary professional radios I've worked on recently (BC348, RCH and RA-1), all of which feature arrays of bulky, complex-to-manufacture and doubtless relatively expensive air-spaced trimmers and their angle-brackets and securing hardware, the RCA (?) trimmers with their small footprint and single hole/nut fixing seem a sea-change in production-engineering terms. They look to be better in self-inductance terms, at least from a low-VHF sort of perspective, too.
|
17th Oct 2017, 2:42 pm | #18 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to disappoint
Now that you point that out they are very simple and elegant and might for that reason have been cheaper to make than air spaced types. So that really makes them a winner, especially with the single hole footprint. I was pretty alarmed when they were missing from the set and I'm glad now I put the effort in to find replacements, it would have been easier just to substitute another part.
One lesson I seem to have learnt over the years with restorations, the harder path is always worth it in the end, but sometimes it is no fun waiting for parts to arrive, some that are wrong or not up to scratch turn up too . But later it seems worth the work. |
22nd Oct 2017, 11:14 pm | #19 |
Pentode
Join Date: Apr 2016
Location: Halesworth, Suffolk, UK.
Posts: 188
|
Re: Electrolytic caps never fail to disappoint
Exemplary work, as usual! I always enjoy looking at your restorations, the patience you must bring to them is remarkable. Vis a vis electrolytics, are there performance benefits attached to their use in specific situations, or is it more often a case of economics? In my various uncoordinated blunderings through various home brew projects, I've developed a habit of using motor capacitors in place of big electrolytics, simply because they're cheap and plentiful, and can be disguised in various ways if necessary. They are, I believe, oil-filled things- they seem to work ok, but I have a fairly crude gung-ho approach to electronics..
Oliver |
22nd Oct 2017, 11:31 pm | #20 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Electrolytic caps never fail to disappoint
Quote:
Modern oil filled and MKT types have high capacity for their size and a 20uF 450V AC rated (which has a higher DC rating) oil filled cap is not dissimilar in overall geometry to a 1930's vintage 20uF 450V wet electrolytic. |
|