26-09-2016, 03:22 PM
One Valve VHF that I built today.
It is a bit untidy on the front end (left hand side) at the moment, because VHF is rather "touchy" to say the least, and using my usual tactics of guesswork, it didn't work initially, although it hissed a bit when I poked a screwdriver down the coil. After making a smaller (very rough) coil, and reducing the capacitance across it from 10pF to 5pF, and attaching a 12-inch rod aerial made from a brass rod stuck in the end of a large crocodile clip, I was rewarded by picking up a broadcast station quite well when poking the screwdriver in the coil again. The coil will need to be remade neatly, and maybe a socket for a rod aerial added. Also, provision for a screw tuning device that pushes a metal rod into the coil in a controlled manner. The components consist of a 955 acorn valve, a 1M resistor, two 10pF capacitors in series to get the required 5pF, a 47pF, capacitor, a .0047pF capacitor and a 100pF capacitor. The output transformer in an LT44. The two coils are wound on empty 1 1/4mm glass fuses in standard holders. These were pure guesswork, I don't even know what swg wire I used, but just filled up the glass area between the ends. (I will check their value after I have the whole thing working as I wish). It is powered by a 6 Volt sealed lead acid and 54 Volts made up from six 9 Volt batteries in series. A few brass nuts & bolts and double solder tags. May be a bit wasteful on brass nuts & bolts, but I got a 1 Kilo tin full on Ebay some time ago for a very low price, and a few days later, picked up another load on a car boot sale.
It will make an unusual and dandy little set once I have tidied up, but now it is working, I have got fed up of it for maybe a couple of days. No doubt it will amuse some of you!
Bob
It is a bit untidy on the front end (left hand side) at the moment, because VHF is rather "touchy" to say the least, and using my usual tactics of guesswork, it didn't work initially, although it hissed a bit when I poked a screwdriver down the coil. After making a smaller (very rough) coil, and reducing the capacitance across it from 10pF to 5pF, and attaching a 12-inch rod aerial made from a brass rod stuck in the end of a large crocodile clip, I was rewarded by picking up a broadcast station quite well when poking the screwdriver in the coil again. The coil will need to be remade neatly, and maybe a socket for a rod aerial added. Also, provision for a screw tuning device that pushes a metal rod into the coil in a controlled manner. The components consist of a 955 acorn valve, a 1M resistor, two 10pF capacitors in series to get the required 5pF, a 47pF, capacitor, a .0047pF capacitor and a 100pF capacitor. The output transformer in an LT44. The two coils are wound on empty 1 1/4mm glass fuses in standard holders. These were pure guesswork, I don't even know what swg wire I used, but just filled up the glass area between the ends. (I will check their value after I have the whole thing working as I wish). It is powered by a 6 Volt sealed lead acid and 54 Volts made up from six 9 Volt batteries in series. A few brass nuts & bolts and double solder tags. May be a bit wasteful on brass nuts & bolts, but I got a 1 Kilo tin full on Ebay some time ago for a very low price, and a few days later, picked up another load on a car boot sale.
It will make an unusual and dandy little set once I have tidied up, but now it is working, I have got fed up of it for maybe a couple of days. No doubt it will amuse some of you!
Bob
