Anyone here every do no solder wire twist circuits?

[gary350]

I am having trouble with these circuit boards so I decided to do wire twist. I have not done wire twist in 40 years. I no longer have my wire twist tools so I had to do this with tiny needle nose plyers. It turned out ok. The wires grip best if the part leads have been tinned with solder first.

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[JimB]

If you mean "wire wrap" connections, yes, I have built one or two things using that technique.

However, what you are showing here, I can only think that they are dry joints in the making.
The tinning wil oxidise and you will have poor/intermittent/no connection.

JimB

 

[KeepItSimpleStupid]

I think your talking about wire wrap pins. They are square pins. You should solder those connections.

 

[audioguru]

The four edges of wire wrap pins cut into the wire wrapping around them to provide a good connection.
Wrapping wire around a round pin makes a poor connection that gets worse when the wire and pin oxidise.
Twist-on electrical wire connectors tightly squeeze the wires together and maybe cut into the wires and hold them together to make a good connection.

 

[ronsimpson]

Wire wrap

 

[atferrari]

Wire wrap

Please, don't talk to me. I still have to wire the last two ICs.

I wonder how was testing that...!

Some twenty years ago I had the chance to see a computer (all TTL wire wrapped) partly disassembled by the technician in charge of maintenance. The cost was 6 digits in USD. Used to process hydrographic (and equivalent) data.

Still recall, the main cause of failures: connectors & pushbuttons.

 

[KeepItSimpleStupid]

Yea, fixing that sort of stuff is difficult, but it was reliable. I worked on a Kevex Auger/SIMS that was wire-wrapped. The unit was pretty old and it lost one color.
Come to find out, it was one WW pin that was supposed to be soldered to the PCB which was power or ground.

 

[gary350]

It has been 40 years since I have done wire wrap I don't remember if pins were square or round. I can not remember anything about the wire I used back then other than is was small and multi color insulated wire. I notice my wire slides off the round capacitor wires so I soldered them and I soldered the wires to the IC. My 1/4 watt resistor wires are perfect size wire to wrap directly to other things.

The Electret mics do not work on any circuits. I removed the mic replaced it with a 8 ohm to 2000 ohm transformer and an 8 ohm speaker. It works but it oscillates, probably because the 2 speakers are only 12" apart.

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[audioguru]

An electret mic has a positive terminal that is powered from a series resistor (try 10k ohms) from a filtered positive voltage and the metal case terminal should be connected to 0V. It has a DC voltage on its positive terminal so it needs a coupling capacitor to the input of a preamp. The LM386 is a power amp, not a preamp when there is a 10uF capacitor between its pins 1 and 8 then it should produce some mic sounds or feedback sounds.

Your 15V supply will cause an LM386 to overheat, use 6V or 9V instead. The 50uF output capacitor value is too small since it passes only high audio frequencies above 400Hz, no bass sounds. use 470uF (43Hz) or 1000uF (20Hz) instead.

 

[ccurtis]

The old wire-wrap connections were very reliable, even in high humidity and vibration conditions. The post corners formed a gas-tight connection with the wire into which air cannot enter, so the connection remains oxidation free even in wet and humid environments. The contact area is so small that pressure of the wire against the post corner is thousands of PSI, maintaining the gas-tight connection in high vibration environments. I am aware of aviation equipment made on large wire-wrapped backplanes that is still in service after over 25 years. The biggest problem with them is sometimes the insulation of a wire routed through the maze of posts would chaff against a post corner if the wire was routed too tightly and eventually cut through. The problem was especially difficult because they were often intermittent.

 

[gary350]

The circuit shows 15 volts but I am using a 9 volt battery.

I probably had the mic connected wrong I did not know it has a + and - polarity.

For my application the 50uf cap might work better at about 100uf I need this amp to read Hz of a running engine. The engines I need to test run about 200 Hz to 400 Hz. I can do the math and get in the ball part but I need to know the real run frequency of the engine. The output of this amp will go to my meter I hope it can read frequency from the amp if the mic can pick up the 120 db sound of the engine pulses.

I will try the mic again across the 10 resistor. I can move the volume control between pin 1 and 8 with the capacitor.

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[audioguru]

An electret mic might not work if it has a 10k volume control directly in parallel. The mic must be powered (it has a junction field effect transistor inside) from a series 10k resistor from a filtered voltage (I show a 1k resistor and a 47uF capacitor as a filter) then it must use a coupling capacitor to the volume control that can be parallel with pin 3 of the LM386 amplifier.

The 1.2k rheostat between the capacitor in series with pin 8 and pin 1 adjusts the gain from 20 to 50 times which is just a small change of level.

Your pulsejet engine looks like it is VERY hot!

 

[gary350]

The engine is very hot but it is hard to get an accurate reading to be used to calculate the run frequency of the engine. Online calculator of a closed tube needs the tube length and air temperature to calculate the Hz of a closed tube. Tube is 21"long and the engine is probably in the 1400 degree F range. Using an infra red temperature sensor it gives me all sorts of readings 800 to 1400 degrees F. Online calculator says 372 Hz for 1400 deg F. Let assume the engine runs at 372 Hz it will suck in 70 degree room temperature are 300 times per second so average air temperature inside the engine is 1400 + 70 / 2 = 735 degrees F that = 219 Hz. Until I know the real Hz of the engine I can not calculate the Hz of the reed engine reed valves. The valves can not flap in the wind like a flag in a tonado they must open and close smooth like the rockers on a rocking chair. Using Hooke's law of physics I can calculate the spring strength of the valves then using gravity and some gram weights I can find how much the valves need to open for them to have a frequency = to the engine. Once I know how far the valve can open I set the stop so they can not open more then they are allowed to open. Now the valves will run at the same Hz of the engine this does several things, it allows the engine to suck in a full load of air/fuel mix, allows the engine to fire with the valves closed, allows the engine to produce maximum power with no wasted fuel, and allows the engine to run with minumum damage to the valves.

All the factory made frequency transducers and detectors are plastic and low temperature so none of them will work. I would buy a Hz detector if I could fine one that can hold up to 1400 degrees F.

The mic has no polarity so I used my meter to ohm it out. I have it connected the correct way now. I changed the 50 uf to 250 uf the amp has a self oscillation problem. There is no resistor in series with the cap on pin 1 and 8.

 

[audioguru]

Hitler's V1 "buzz bombs" were the most dangerous when the buzzing stopped.
Audio feedback will not occur when a speaker is not connected to the output of the amplifier. Use your 50uF output capacitor to feed a 100 ohm resistor instead and connect your frequency meter to the resistor.

 

[tunedwolf]

What kind of engine?, or is this a hot tube ignition system for it?

 

[gary350]

What kind of engine?, or is this a hot tube ignition system for it?

That is a small pulse jet engine.

 

[audioguru]

The pulse jet engine is much less expensive than a jet turbine engine but has similar power and efficiency. I read about it in Google and saw videos of some radio controlled model airplanes flying extremely fast with a noisy pulse jet engine.

 

[gary350]

This is the tested and proven circuit.

After learning the Electret Mic has a polarity and getting it wired correctly with the 10k, 1k and 100uf cap it works. I am surprised this little Electret mic it has a good sound and good pickup.

Sound quality is very bad lots of distorted.

I removed the capacitor between pin 1 and pin 8 that made a very big inprovement in sound quality gain drops to 20. Volume control in series with cap was not very much improvement and different size caps are no help either.

The 10k variable resistor is useless, turn it just a little and there is no sound at all. So I replaced the variable resistor with a fixed resistor. I should have experemented with a 20k, 50k and 100k variable resistor.

The 10k resistor needs to be connected directly to pin 3 with no capacitor between pin 3 and the resistor.

The .1uf cap between pin 3 and the mic works perfect, I experemented with several other caps .1uf works best.

I experemented with the 100 uf cap at the ear phone, I changed it from 50 uf, 100 uf, 350 uf, 470 uf all this does is make the signal have lower Hz base sound and no effect of the bad quality sound.

30 years ago I use to know what the bypass capacitor on pin 7 is for but I can no longer remember and don't remember where too look it up. I removed the .05uf cap and sound quality appeared to be worse so I tried several caps even a 10uf then finally went with a .1uf cap.

After several parts swapping experements sound quality is 100% better. Sound is best with a brand new 9v battery.

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[audioguru]

EVERY electronic circuit needs a capacitor across the power supply. Yours is missing so the supply voltage is bouncing up and down with the output signal of the amplifier and it gets amplified and might even cause the amplifier to oscillate at a very high inaudible frequency that causes distortion. Use 100uF.

You removed the capacitor between pin 1 and pin 8 so the gain of the amplifier is very low (20 times) for a microphone input. Then the sound level must be VERY loud for the output level to be strong and then the mic might be overloaded.
If the output level is too high then the amplifier clips it causing severe distortion that happens with ANY amplifier. A brand new battery voltage is high so the maximum output level before clipping is also high.

The datasheet for the LM386 shows a 10uF capacitor from pin 7 to 0V.

 

[gary350]

Very good information. I need to get use to checking data sheets online. I keep trying to find information in old books. I changed the bypass cap on pin 7 to 10 uf. I added a 100 uf cap in parallel with the battery. Sound quality is very good and loud enough to amplify a pulse jet engine.

Small pulse jet engines run at a higher frequency than larger pulse jet engines. Some of the guy with engines say they are 130 to 135 db. The larger engines are in the 120 db range. My new improved 5 lb thrust engine is producing 7 lb of static thrust and probably 10 lbs of thrust at 200 mph.

I am leaving the amp with a gain of 20 it is plenty loud with ear phones. 120 db might be too loud if the amp chips I might get a bad reading on the frequency meter.