EEVblog #574 – NEC Analog TV IF Modulator TeardownPosted on January 29th, 2014 6 comments
Dave looks through the documentation for the vintage 1980 NEC PCN-1205AH 5kW Analog TV Transmitter that used to transmit the CH7 TV frequency in Sydney
He then tears down the HPA-3696 IF Modulator used in the system.
Facility tour HERE
thanks Dave – always look forward to your videos – keep ‘em coming!
Thanx much dave, looking for digital transmitters teardown too, Australia use, I think dvb-t broadcast systems.
Really enjoyed that teardown, and those dense manuals remind me of when manuals were proper manuals!
Well done mate on blagging that top-end kit.
Karl T (UK)
Dave thanks for the videos!
Really cool and rare stuff.
Greetings from Greece!
Dave, what a great video. When you post the scans of the two manuals, could you include some high-res photos of the individual boards and case to correlate with the manuals (since we all don’t have access to the hardware)? thanks, jon
Those electrolytic capacitors in there are SOLID TANTALUM and only second in quality to thise used in military gear. (The replacement aluminium electrolytics probably replaced similar aluminium electrolytics in less critical parts of the cricuit as those tantalums simply NEVER fail unless you reverse polarity them). Under that clear sleeve there is a tin plated brass can. The inside of the can soldered to an electrolytic seposit of pure silver over manganese dioxide graphite mix which forms the “cathode” of the capacitor. The “anode” lead passes through a “feedthrough” made of two concentric plated brass rings with some low melitng (often army green coloured)glass/emamel in between the two and the lead passing through a hole in the smaller centre ring and soldered to it. The outer ring is soldered to the brass can. Inside, the copper wire is spot welded to a tantalum wire and this is spot embeded into a large sintered billet of tantalum metal which fills most of the interior volume. Between the billet and the silver plared lining of the can the space is packed with manganese dioxide moistened with some electrolyte. This oxidizes the surface of the billet to give it a deep steel blue hue. This is a very thin layer of Ta2O5 and is the actual dielecric.
The mil spec ones have the WHOLE OUTER can fabricated from stirling silver (alloy of 95% silver and 5% copper to harden it) In the bottom of the can is slipped a Teflon three fingered jig which holds the tantalum billet in place. A conductive jelly which looks like snot filles the gap between the blued surface of the billet and the silver can. To seal it in a teflon washer is slipped over the tantalum “anode” tail wire then a silicone rubber gasket, usually army green in colour. The silver can is “crinched” around these polymer components in much the same manner as a cheap aluminium electrolytic’s can. The solderable “anode” wire is spot welded to the tantalum tail wire outside and is easily seen in these high quality capacitors.
You can always pick these capacitors because of their high mass density (because of the huge slug of dense tantalum inside).
If you are game, Dave and wish to trash a $20 capacitor, take a small one out, say a 1.0 or 2.2uF one. (You could then replace it with a monoblock ceramic withou compromising the function of the original circuit). Lay it on the bench and peel the plastic off with the side cutters. Now put the soldering iron tip on the side of the can and solder to it (don’t worry, it won’t go BANG), when it is hot, pull the anode lead and the spacer and billet will simply slide right out. All the guts is held in with solder! If you bang the slug with the bull nose pliers all the manganrse dioxide will crumble off and leave the slug of rare tantalum metal.
I have wrecked so much of this “Rolls Royce” gear that I have drawers of these solid tants “to burn”. They may be second hand, but even second hand the quality is so high they are yards batter than most new, off the shelf electrolytics. Their ESR is quite low and their leakage is almost non existant. If I need to build a circuit in a tin can to go in a dirty, damp or submerged location and I need to pass a conductor through the side of the can which must carry R.F. and the stray capacitance must be kept to a minimum, I sacrifice one of these tants for the spacer, solder it into an appropriate sized hole in the can or bulkhead and pass a component lead through its wicked-out centre hole and solder the lead in place and “Wholia” an envoronmentally tight signal feed through.
Otherwise these tants are great for bypass or timing applications.
Leave a reply