Since I do a fair amount of designing and repairing of tube
based amplifiers,I decided to build a simple tube tester.It tests output tubes
such as 6L6,6550,EL84,EL34,and 6V6.The circuit is very simple.
A transformer powers the filament ,while the plate voltage comes from the
rectified and filtered power line.The switch in front selects the different
grid voltages needed for the
different tubes. I've found the tester very useful in matching output tubes for
amplifiers since it shows me the actual current through the tube.
The wood is redheart and the top is black acrylic.cost:$93.74
Here are some microphones that I have designed and built.
A.a scratch built ribbon mic.(shown in the center)
This is the first and probably the last microphone I will ever build from scratch.
Construction is pretty simple and straight forward.A thin piece of aluminum foil
is suspended between two steel bars with two very strong magnets behind them.
The output goes to a small step up transformer.
Even with the 20db preamplifier,E, I'm amazed how low the output is.The overall sound is good.the bass is low but the midrange has good detail and the treble is good.
Unfortunately, the ribbon element is mounted to the back of the enclosure which does ring on loud passages.Gluing a piece of thick rubber with silicon glue reduces the problem.
B.stereo electret microphone.
pair of electret microphone elements are mounted on a piece of acrylic suspended in a pencil holder I bought at an office supply store.A nine volt battery powers the circuit.Close up of the interior at the far right. sound:The sound is very good.Can be used for serious recording.
C.stereo dynamic mic.
This microphone uses two 1" dynamic elements.
The two elements are glued to a thick piece of plastic and held inside with
Like the stereo electret mic before,the top of the case is a pencil holder and the bottom is a paper clip holder I bought at a local office supply store.
sound: The sound of this mic is ok at best,I've tried many different elements and found them all quit disappointing in the sound.The only thing good I can say, is it doesn't need a power supply, and it was cheap to make.
D.stereo electret mic.
Two electret elements mounted on the left and right side
of a plastic case.A 9v battery powers the circuit.
This is a very good sounding mic. the bass is good and the midrange has very nice detail in it and the treble is very extented.the only negative point is the case is not a dead as I would like it,and it does color the sound a bit.
total cost for all mics $52.08
conclusion B was the best sound and can be used for pretty serious recordings.D was a close second ,the only different between this mic and B was that case doesn't color the sound.A the ribbon came in a distant third,it has a nice detailed sound but the output is just too low, the preamplifier I built boosts the output to a usable level but adds a noticable bit of hiss to the sound.Dead last was C.I've tried many elements and I found them all at different levels of disappointment.
All microphone sound tests were done with me playing my yamaha acoustic guitar at a distance of about 2 ft,with mics plugged directly into a TEAC tape deck.
My latest mic.I used very thin ,small loudspeakers that use a piezo cermaic diaphram element. They are very bad as speakers, but they make good mic elements.I epoxied them on some oak and mounted them in a blumlein pattern(crossed figure 8).It does have a little more hum than I like, but over all the sound is very good.
Another stereo electret mic.The elements are from digi-key.And I'm using
a regulated power supply in a seperate case,not a battery.The mic case is from an old mic from the 50's.The sound is very good.
Although I have many digital meters,I felt it would be interesting to have an
old fashioned analog meter. The design is about as simple as you can get.The meter
itself is a center type, this way I dont have to switch the leads around if
I'm measuring a negative voltage.The DC voltage ranges are:5V,50V,500v. And the AC
voltage range is:50V,500V.The top is acrylic and the wood is wenge.cost:$25.61
I've made many electronic projects,but never the components that make then up,so I decided to delve into this area.On the right, are some resistors I made.Making resistors is easy , there are many items that exhibit resistance. The two I used are conductive foam and nichrome wire.Nichrome wire makes very accurate resistors but not very large in value.Conductive foam create large values but are very difficult to get a exact value.Both are coated in an acrylic paint which when dry provides a nice protective layer.On the right is some capacitors I made.The 20 pf is 2 pennies with a thin plactic wrap material as the dielectric.The 800 pf and the orange cap is wax paper as the dielectric and aluminum foil as the plates.Each was a foot long and then wrapped in to a coil.Both the 20pf and the 800pf uses black paint as the protective layer while the orange cap uses wax.The last is a much larger value. I used a much wided and longer strip of wax paper.Its encases in a cigar holder potted with wax.
Many musicians have requested that I make a solid state version of the famed 5U4 recifier.This was very easy, I simply used 2 1N4007 silicon diodes in an octal base.The other is the same except I've included a 200 ohm resistor in series to simulate the natural resistance the 5U4 tube has.
click here for pictures of my vacuum tube collection.
Man's mind, once stretched by a new idea, never regains its original dimensions.