What is it, do you have it, and what to do about it. Shango66: IF Silver Mica Disease Capacitor Value Identification • IF Silver Mica Disease... TV mug available here: society6.com/product/old-tvs-...
The M tester is accurate enough to measure those capacitors if you can get the whole wafer out as one piece. Not really something for the Casual radio collector you have to be pretty serious to get in this deep
I was just about to comment that I prefer your method of reverse-engineering to find the values, gut the mica wafers & reassemble can with trimmer caps then peak the IF using the caps & measure what you get. Much nicer result than measuring even mildly-faulty originals & lots nicer than some folks "they're all about 100 puffs" job.
@@shango066 They're pretty good little tools, just found the limitations of mine the other day though in working on an old signal generator. It "only" measures down to 20pf
Silver 'mica' disease , ,but more specific it's Silver Migration Disease. Where the ions migrate from one side of the mica sheet, to the other. It's all good. thank you for the video.
if you need to have that disc recoated, its not that hard for me to do. Id simply remove the original silver with acid, then recoat it in an evaporator using a pattern mask. I can even plate the silver in aluminum to protect it longer. As for the values, seems like it should be easy to calculate the values of it. then again, im used to this sort of stuff. edit: should add that in order to do this, i need very good reference photos or an original disk to create the pattern masks and measure the silver thickness originally used. edit2: funny enough i have period accurate equipment to recoat the disk. i just find this amusing
@@donsurlylyte just one snag to this, i would need an original (even damaged) example to reverse engineer. Creating the actual coatings is a routine thing for me, as i do it in my lab on a regular basis.
If you were doing this for others and charging a reasonable amount for your time, how much would it cost to do these? I suppose the first ones that you would do would have the most labor and later ones would benefit from having the information and patters already made.
Bob, very interesting video and thanks for sharing with us a lot of what I have experienced myself as well in restoring old radios and TVs and dealing with which type of IF transformers have the silver mica disease and which do not. Very interestingly, it appears that Admiral used two types of almost the same tuner, I believe both made by the Standard Coil Company, where one type uses a square IF can on top of it that does have internal mica capacitors that can get silver mica disease, while other models had a very similar tuner but where basically the same coil and capacitors are inside the tuner but use external capacitors and therefore likely do not get SMD. Both models of the Admiral TVs you showed here have the type with the discrete capacitors, but I recently worked on a model 19A11 7" electrostatic type that had the square can and did have SMD, causing the picture to jump all over the place, and almost appeared to be a vertical problem at first, until I traced the noise and intermittent DC positive voltages coming out of the tuner output. Shango066 did a video on this recently, and I found my set to have the same problem!!
Wow that was a bucket load of information!!! 👍So glad you did this video. I have not seen as comprehensive a take on silver mica disease as you have presented here.🥇 I like the way you talked about the evolution of circuitry over time in both radios and televisions. In that regard I was especially intrigued by the adjacent channel traps in one of the sets. That was some fancy engineering! I had to go back a couple of times because I found myself getting distracted visually by two things, your television themed coffee cup and what looked to be a red RCA pin tube straightener. 😃
Ha ha. Glad you enjoyed it. Some of those early sets were a bit over-engineered. The reality ended up being that there were no adjacent stations in any broadcast area. So the IF response didn't need to be quite so sharp. I'll be doing a video on IF theory and circuits someday. Perhaps a mini series. One each on AM, FM and TV. That is indeed an RCA tube pin straightener. I added a link to the mug in the video description.
The IF cans with the plastic interior has those silver mica plates. Yes, you get migration but the connections are via spring contacts. I have a Hallicrafters S-56 that has these bad IF cans. Pull the mica caps out and the areas where the contacts touch the mica are all silver, black, blue and yellow. All kinds of odd corrosion. I think there is some galvanic corrosion between the silver, the metal contact and whatever it is plated with.
The change in IF design coincides with radios moving from kind of a 'luxury' item to a consumer commodity item. This wass hastened, I think, by the rise of commercial television. Radio had to get less expensive, because people would not spend as much for a radio as what the could get a tv for. Also, radio was moving from the primary entertainment medium to a secondary stream. So, the receivers had to get smaller, as well as cheaper. Manufacturers began building them to a price point. Pennies mattered in costs. IF xformers with adjustable inductors were cheaper to make than those with variable capacitors. It all comes down to money.
The more I watched this video it explained the behaviour of a 1940 English radio I have. I had been blaming the odd behaviour of the oscillator on a substituted frequency-changer tube. 6K8 for 6A8. The bitch crackles too
Most schematics don't show the internal values, so I disconnect one side of each winding and measure the value with a Z Meter. Most are 100pf to 120pf. I remove the mica sheet and put in fixed caps. Cleaning the mica between the sections also works but it's easier to add caps than to try to replicate the drilled out rivet. If it unscrews, cleaning the mica will give it another 25 plus years.
Well we recapped it months ago and there's no footage. The original tweeters are shot which is a common problem. Maybe we'll do a video on repairing the IF cans and replacing the tweeters.
I had a Motorla 52H that had that crashing sound and would short out. I sprayed (a lot) of Deoxit on the bottom of the IF cans and its been working fine since 2011. Go figure.
Hi Bob, my Zenith Transoceanic has IF transformers like those. It had SMD disease and I used the eraser method. Works great and not hard to do. I figured it took 60 years to get that way so it will probably take that long to get that way again. I repaired several 1930s radios with open IF coils where the break was underneath the winding. I just unwound the coil letting the wire drop on the floor and rewound it by hand using the same old wire. Dripped candle wax all over it and 'mushed' it with my fingers making a redicuously terrible looking bird's nest. Looks like it will never work but it will peak at IF frequency and work great. No more worry about sourcing new if cans ! Even if the wire had several breaks and falls apart in your hand I have had success by lengthening the wire with approximately the same guage and length.
I'll have to add this eraser trick to my other eraser tricks. It was nice that you showed the guts of the other coils. I especially liked the trapped coils. What or where is the best reference for finding an IF can's specification, based on part number ? I think some NP0 ceramic caps are marked using a black "dip" at the top. Do you happen to know when the black dip indicator started to be used ?
The only place I've seen IF can specs is the replacement catalogs from J.W. Miller, Merit, Thordarson etc. I'm not familiar with black dipped NP0 caps.
I wonder if any "dark room" chemicals would help. After all, those are all about accelerating and stopping the oxidation of silver deposited on photo-sensitive film and paper. Interesting video! Thanks for posting.
Nope. I don't know why all the weird suggestions of plating the mica sheets, or using chemicals to an already damaged mica sheet. Some have been able to scrape the migrating silver away, reinstall the mica sheet and it sometimes works. Later though it will return. The silver migrates right over the edge of the mica sheet. There are indeed spots on the mica that NEED to be there. Taking a sheet out and scraping off dark sports will render the mica sheet useless. The shaped spots on that mica disc need to be there. The 'bad' spots is around the edge of the disc. The black stuff that has traveled over the other side creating the short. It makes sense while in there to replace the mica sheet and install a new fixed cap, or remove or disable the sheet and add new caps under the IF can after re installation.
Thanks, Bob, now it makes sense. I didn't realize that the majority of television IF's didn't use the mica wafer in the bottom of the can like later radios did. As an aside, RCA did some wacky stuff with radio IF's immediately after the war (model 56X2 comes to mind). Some of their IF's will have the traditional 2 adjustment screws on top like early 40's radios did, but they also used 2 fixed-value mica wafers inside of the can---I've had to replace those
To everyone: 𝐌𝐚𝐧𝐲 𝐩𝐞𝐨𝐩𝐥𝐞 𝐬𝐭𝐢𝐥𝐥 𝐭𝐡𝐢𝐧𝐤 𝐭𝐡𝐞 𝐚𝐝𝐣𝐮𝐬𝐭𝐚𝐛𝐥𝐞 𝐭𝐫𝐢𝐦𝐦𝐞𝐫 𝐜𝐚𝐩 𝐭𝐲𝐩𝐞 𝐨𝐟 𝐜𝐚𝐧𝐬 𝐢𝐬 𝐢𝐦𝐦𝐮𝐧𝐞. 𝐓𝐨 𝐭𝐡𝐞 𝐚𝐝𝐣𝐮𝐬𝐭𝐚𝐛𝐥𝐞 𝐩𝐚𝐫𝐭, 𝐲𝐞𝐬, 𝐛𝐮𝐭 𝐭𝐡𝐞𝐫𝐞 𝐢𝐬 𝐬𝐨𝐦𝐞𝐭𝐢𝐦𝐞𝐬 𝐚 𝐅𝐈𝐗𝐄𝐃 𝐎𝐔𝐓𝐏𝐔𝐓 𝐅𝐈𝐋𝐓𝐄𝐑 𝐜𝐚𝐩 𝐦𝐚𝐝𝐞 𝐟𝐫𝐨𝐦 𝐦𝐢𝐜𝐚, 𝐬𝐚𝐧𝐝𝐰𝐢𝐜𝐡𝐞𝐝 𝐮𝐧𝐝𝐞𝐫𝐧𝐞𝐚𝐭𝐡 𝐭𝐡𝐞 𝐚𝐝𝐣𝐮𝐬𝐭𝐚𝐛𝐥𝐞 𝐬𝐞𝐜𝐭𝐢𝐨𝐧. 𝐓𝐨𝐨𝐤 𝐦𝐞 𝐚 𝐰𝐡𝐢𝐥𝐞 𝐭𝐨 𝐟𝐢𝐠𝐮𝐫𝐞 𝐭𝐡𝐚𝐭 𝐨𝐮𝐭. 𝐒𝐢𝐠𝐧𝐚𝐥 𝐭𝐫𝐚𝐜𝐞𝐫 𝐬𝐡𝐨𝐰𝐞𝐝 𝐧𝐨𝐢𝐬𝐞 𝐀𝐅𝐓𝐄𝐑 𝐭𝐡𝐞 𝐈𝐅 𝐜𝐚𝐧, 𝐛𝐮𝐭 𝐧𝐨𝐭 𝐛𝐞𝐟𝐨𝐫𝐞! The SMD had to be in the can. Looking at the schematic I saw a fixed cap, and found it was inside the can as well. Disassembled the adjustable section (it was all on the secondary side) and behold the fixed cap. That was the one with the SMD. Hidden and I suspect many would not pinpoint this hidden fixed cap. Reassembled the can, leaving out the fixed mica sheet, added that fixed cap under the chassis and the set played fine. I can't remember what make and model it was. 𝐒𝐨 𝐬𝐚𝐲𝐢𝐧𝐠 𝐭𝐡𝐚𝐭 𝐭𝐡𝐞 𝟐 𝐬𝐜𝐫𝐞𝐰 𝐭𝐲𝐩𝐞 𝐭𝐫𝐢𝐦𝐦𝐞𝐫 𝐜𝐚𝐩𝐬 𝐚𝐫𝐞 𝐢𝐦𝐦𝐮𝐧𝐞 𝐭𝐨 𝐒𝐌𝐃 𝐢𝐬𝐧'𝐭 𝐚𝐥𝐰𝐚𝐲𝐬 𝐭𝐫𝐮𝐞(as you've mentioned here) Please keep that in mind everyone when you cannot find the SMD source location.
Greetings: Only IF< transformers with iron core tuning adjustments instead of ceramic trimmer adjustments have I seen or heard of SMD. Servicing iron core IF transformers with SMD usually is done by removing the offending mica caps and replacing the caps with fixed value poly caps after the appropriate values are determined. If the schematic shows the values - great, if not then a temporary ceramic trimmer that is expected to cover the required range is used to resonate them at the IF frequency, then measure the value and sub with a fixed value cap. Each method still requires IF alignment that should be within the iron core tuning range.
Here is something you can spread the word on. There are indeed "some" cans with the screw trimmer caps that can get SMD. No, not between the screw trimmers, but in the HIDDEN fixed cap inside of some of those cans. Where is the hidden cap? It is sandwiched underneath the screw ceramic/mica trimmer assembly. The Secondary side only. This fixed cap is the 'output filter' Many times it is separate from the can, however some manufacturers used an IF can with this output filter built inside. I found the SMD noise in a set, I forget the make. The IF cans were the typical ceramic screw trimmer type. So, I thought the SMD was coming from elsewhere. Wrong! Listening to the stage before and after with the Tracer, I pinpointed the noise source to the can. ??? Strange as I have not seen that before in the 40years of radio work. I disassembled the ceramic trimmers, unbent the tabs gently. to reveal a second FIXED cap mica sheet on the secondary side. I mounted a fixed cap electrically the same position, reassembled the screw trimmers. The set played perfectly now. So if someone has the SMD noise we all know of, and you have a conventional IF can, look at your schematic to see if there is a fixed cap on the output side of the IF can. Even though you have screw trimmers, this hidden cap may be the source of the SMD. I have photos of the job someplace. 99% of the time though the noise if from the type of can we all know about with the SMD issues. Fixed mica sheet for pri and secondary, and the coil for both sides. Keep that in your toolbox in case there is ever someone out there that cannot solve their SMD with a conventional IF can.
I wondered that! It reminded me of an early RCA horizontal osc coil as well used in models like the 8TS30, it is a square can where it has a primary and secondary, one adjustment is the frequency, which is the knurled knob that will protrude from the outside of the chassis (coarse horizontal hold control), and the inner slug is the primary which is the "phase" adjustment for the AFC circuit.
See the drop down description. He has a link to Shango066 that will show you the part you are asking about and the procedure to determine the value if you can not measure the original mica condenser value.
People on the Internet spend way too much time stressing out over this, almost as much as they stress out about capacitors and spraying Deoxit all over the place.
@@bandersentv I have seen it misdiagnosed online, many, many times. It’s not as common as it’s made out to be. Much more common on newer AA5’s. Communications receivers, not so much.
@@ArthurJS123 I understand what you're saying, it is like how some meds are over prescribed, without proper testing. Same with automotive sensors or actuators. There is a lack of knowing how to pinpoint an issue. Voltage measurements or listening to the stages help narrow the bad spot down. Over the 40+ years I have been in the hobby, I have only ran into true SMD 10- 15 times total. I have never had to deal with SMD on a boatanchor, or any communication receiver, yet :)
If youre repairing the radio, 30 Bucks in capacitors IS worth it. Else, ebay the radio in stock configuration and go buy a new, disposable, digital radio.
You have a problem that took 40, 50, 60, or 70 years to develop, is a combination of exposure to the atmosphere (the tarnish) and hours of use (the tendrils). So, if you clean the silver, remove the tarnish and the tendrils, why wouldn't you expect to at least get years of service before the problem reoccurs?
@@bandersentv I was also thinking of fine silver polish. That contains some chemical to reverse/remove tarnish (silver oxide) and an extremely fine abrasive so as to not damage silver plating. That might be applied with a microfiber cloth or cotton swab. Of course, doing anything risks damaging the surface. But then you are back to replacing the cap.
@@BryanTorok What is needed is to remove only the migration from one side to the other. No need to polish the silver 'pad' where the contact touches. Polishing it can wear the pad down and change the capacitance. Plus, while the sheet is out, why not replace it with more of a permanent fix"? Fixed silver mica capacitor. After having the IF can out, we only want to do a repair once, and using materials better than factory.
@@bandersentv ...it's also a coil and a capacitor in SERIES across a short circuit: it depends on where the signal is applied/ picked off. If it's a signal trap, shouldn't it act like a low impedance at the specified frequency?
@@bandersentv there is a cap in T2 it's .00015 not sure if it would be fixed or not. The radio works but the audio is distorted. And stations are weak. Looking inside from bottom of radio might be a disc. If I touch tuning cap audio is clear
@@bandersentv I suspect coating the 'repaired' mica sheet with anything will change the capacitance. It took 50+ years for the mica to get bad, it may take another 50 before it goes bad again. And then, who's to say that silicone can prevent ions from traveling across it? I mean, mica didn't stop the silver ions from traveling across it, it would go across anything just about. I am not a fan of the erasing and scraping the old mica sheet. Yes, I have done it before, just because on my own radio. Using external or dipped caps you pretty much prevent migration between the 2 new caps.
@@watcher818 All great points. I'd also like to add that in this design the silver needs to make electrical contact with metal pads to complete the circuit. A coating would interfere with that.
@@bandersentv Thank you sir. Anything like you said like lubes, cleaners or coatings will indeed change the capacitance. Many of us have accidentally sprayed a tuning cap and the trimmer caps with cleaners. Fast drying kind will evaporate, but some may permanently change the trimmer values. SMD is straightforward as far as a permanent repair. You are right also that those silvery pads on the mica sheet need to be there for contact. That part is the contact and should never be scraped off. The offending migration path travels from that pad, all the way to the other side of the mica sheet. While many here have good intentions to solve or prevent the issue from happening, I see a lot of 're inventing the wheel'. Replacing the caps inside, or on the IF can lugs, will be a permanent repair. Regards :)
The capacitance would not be the same. Not only would it need to be exactly the same dimensions, but a piece of metal pressed against mica is not going have the same properties as silver deposited onto the mica.
There is a spot of silvering placed on the mica originally, It is specific size to determine the capacitance, from the top of the sheet to the bottom. You can't remove the original silver of course. It may be hit or miss on getting the 'migration'. If it's on the surface, sure. Sometimes though this migration can get between the natural layers of mica flakes. You can't clean it out of there. Some have scraped down into the mica to get the discoloration off. I don't know if removing some 'bad mica' will change the capacitance. Or if it will come back again soon. While in there why not just replace the mica sheet with modern parts under the chassis ? Myself, I only want to do a job once, especially if it is not my radio.
