I love building. The biggest reward in creating a circuit is watching it work when you fire it up. One of my first projects, when I was first licensed in 1975, was to build a 3 band trapped diploe. I used molded mica transmitting silver mica capacitors and B&W coil stock. Once the traps were constructed, and checked with a grid dip meter, they were ready for installation into the wire antenna. Through the years, ceramic doorknobs became more common place than the old micas, I suppose due to availability and not form, fit and function. The mica was and always will be a superior capacitor for use in and outdoor antenna trap. That 20-40-80 meter dipole worked faithfully for many years.
Molded silver micas are made with a hermetically sealed envelope, impervious to weather of all sorts where and the doorknobs are made from porous ceramic. They don’t hold up to the Midwest elements like snow, ice, water, freezing and thawing. Eventually they pop apart. The mica is great for small traps made for a 200 watt or less transmitter and will last a long time. Micas are made both with solder terminals and screw terminals. I prefer the screw type. They have 6-32 solid brass tapped screw holes and can be soldered if you insist and a tight mechanical connection is made. The solder joint is also subject to weather over time. Micas are also available in literally hundreds of values allowing latitude in design and the ability to change values sliding the resonant frequency of the trap a little if need be. It is not uncommon to parallel molded micas as well. Micas are 30%-60% less than the current cost of ceramic doorknobs. RF current handling is greater for the silver mica.
Too many new hams take the easy route of a random wire and an antenna tuner. Live a little. Build traps. If you can’t find coil stock, wind your own inductor on 3” thin wall PVC. Used 10 gauge enameled wire and then urethane the winding in place once its wound. We also have ceramic insulators you can run through the middle to take the strain off of the trap. There lots of construction stories on how to build traps. Try the Radio Amateur’s Handbook for example.
I made these traps early in my ham career. Conveniently, the same year Jim and I started Surplus Sales. So, for the next 40+ years of buying parts for the surplus business, I always kept an eye out for silver micas. Handy little buggers. They have also been a great seller through the years. We have not raised prices on these for decades. And to make matters even more tantalizing for the reader contemplating building an old fashioned trapped dipole, I acquired another 500 pounds or so of molded silver mica caps to add to stock. Not much chance we will run out anytime soon! Check out our web page for micas and keep an eye on it as it expands very soon! Fistell Electronic’s inventory has only had the surface scratched but we just found a pallet of micas during our move to the new building.
Forty one years of searching for good quality parts has been a blast. A treasure hunt. I have had moderate luck finding vintage components and enjoy selling them worldwide. Occasionally, we can no longer locate certain mechanical parts that our customers desire. So we contract to have them made. Fighting the urge to stock what everyone else does. Import that. Knock-off this. Well, recently we were put in the corner by a manufacturer we have used for decades. One product they made for us for many years has slowly degraded with poor workmanship and inferior components. The last batch was rejected for multiple reasons and I needed to decide whether to continue with our trademark Turns Counter we have sold for 25 years, or retire it. What happened next was a complete upgrade and rebuild. My dad always said “If it’s worth doing – it’s worth doing right!” We took on the full production of our magnificent counter and now have something we are proud of.
SHW-TCV Turns Counter – Mechanical
“Since every piece of equipment that uses a turns counter has no capacity for skipped turns, we solved the problem.”
We started over at ground level. The main problem other knock-off counters have is the shaft moves laterally when the knob is cranked. This action in turn causes slop in the gear placement which in turn interrupts the counting. Since every piece of equipment that uses a turns counter has no capacity for skipped turns, we solved the problem.
Turns Counter – Front
In our counter, the shaft is locked in place both in forward and aft lateral moments. Another feature of the rejected counter are extremely cheap plastic gears. They are held in place with friction and are inferior at best. We have solved the problem with stainless steel miter gears made exclusively for our counter. Our new SHW-TCV Turns Counter is now flying off the shelves and can be found on commercially produced equipment in the medical world as well in amateur radio projects.
Maybe it has more to do with the fact I know the quality of a US-made part is historically high. An import is more of an unknown. It’s not a coincidence that most of our millions of vacuum tubes are NOS (New Old Stock) , largely US with a handful of European makes. The ONLY parts we import, in over 200,000 line items, are a line of coaxial relays, a solid state relay, adhesive tapes and a few rf connectors. That’s it! Beauty is in the eye of the beholder… or maybe just the peddler. If the seller has US made products, chances are, his price is higher than for an import. If he only has imports, he will tell you they are just as good as any US made part. In particular, the subject today is vacuum tubes.
Most tubes dealers have had the opportunity to buy off shore valves, including Surplus Sales. Many manufacturers to choose from, Chinese, Russian, all of which will sell you their product branded any way you want it. Your brand, their brand or something new. Whether you have a US-made NOS or a new import, what separates a “must have tube” from one better off in the trash can comprises variations in raw materials, tolerances and workmanship. We dropped the imports and have had to do without a complete lineup as many numbers slip away to oblivion in the NOS world.
5U4GB’s have been hard to find for years. For Surplus Sales it is one of the highest demand high power rectifiers we have ever had. Most dealers today run prices from $30-$50 for what precious NOS stock they have left. I am happy to announce we have secured a portion of the last remaining government stock of Philips JAN 5U4GB vacuum tubes, manufactured from 1985 to 1987. This is arguably the finest 5U4 available today. US made for our military’s radio equipment, likely of Rockwell Collins manufacture. Due to the large quantity of this premium 5U4GB now available we can offer a price from decades ago. Starting at $24 with deep discounts to $15 each when buying in quantity. Stock up now. Once our inventory reaches a preset level, the deep discounts will cease.
In addition to the great news on our Philips JAN 5U4GB, we have cut prices on all remaining new and removed 5U4’s to reflect a proper relational sale price compared to the Philips. This is a golden opportunity to stock up. Once these are gone, there will be no more!
Guest Writer: Bill True, WA9 ASD
There are a number of tubes that appear to be ‘under the radar’ of tube equipment designers for no apparent reason. One such tube is the Sylvania 6888. Originally designed as a core driver in first generation vacuum tube computers, it is practical in several other applications.
Multiple versions of a one or two tube AM Broadcast Radio project might be responsible for bringing this tube back in demand. We found a half dozen worthy construction challenges on the Internet. The 6888 is used for an AM transmitter to feed a signal to antique table radios. Using modern input sources, we think there is an un-tapped potential as a low power audio application like a headphone amp or personal stereo as well. If availability or cost were deterrents in the past, we now have enough to go around. With over 10k in stock we offer a 1 each price of only $3.95 and it drops to $2.50 ea for a whole case of 100 at a time. See our tubes at SurplusSales.com
Let’s skip the paradoxical complication of a wireless connection and the questionable sound reproduction of antique radios and go right from source to speaker. No limitation of 5 Kc on the top end that AM stations are subject to. No misaligned IF section that misses the detector pass band. No risk of leaky filter condensers and torn paper speaker cones. Let’s just put a little gain and some impedance matching between the source and some good, wide-range headphones or speakers. Worst case; hide the good speaker in the antique radio.
While the 6888 is kind a power hog on the filament side it is definitely a pussycat on the plate side with moderate if not low voltages and current required. Because of this it shouldn’t need some exotic hand-wound high plate impedance transformer to match the load. A couple of thousand Ohms ought to do it.
As a voltage regulator, another great idea for this pentode, it should be nearly indestructible and will probably out-last the resistors in the circuit. It would have considerably more current capacity than a VR-150. We will be happy to post on this site any project using the 6888 and give credit to the author.