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 Hints and Kinks

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Cliff Jones
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PostSubject: Hints and Kinks   2012-02-04, 3:58 pm

Went to the antique mall and came up with a couple of Ideas.
Antenna insulators for long wire antennas are getting hard to find at a reasonable price so why not use Telephone glass insulators Cool $2-$3 each
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Need some shunts for meters? Well look no further than a toaster or electric Dryer (Hair or clothes). They all use Ni-chrome wire for the heating element. And has a positive temperature or neutral coefficient.

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PostSubject: Want better sounding small speakers?   2012-02-11, 7:38 pm

Hints:
Sometimes that radio sounds tinny, it can be caused by dust and metal between the speaker coil and magnet. Clean the residue out very carefully, sometimes just blowing air can solve the issue, but most of the time it takes tedious work to remove those metal filings. One way is to use scotch tape to touch and hold the filings. Once the voice coil is clean there are a couple of solutions to help prevent this from happening again. Usually the 3 to 4" speakers have a light felt covering the area to prevent dust. To improve this situation is to take a flat piece of plastic and cut it to just cover the speaker voice coil hole. You can take a pencil and a fibre or metal washer as a template and draw the outside edge of the washer onto the piece of plastic or heavy cardboard. Then either use scissors or a razor blade box cutter to cut the circular pattern on the plastic.

When finished cutting the disk, add a thin coat of silicon or rubber cement on the outside edge of the speaker coil. Carefully put the plastic disk over the adhesive while centering the disk. let the adhesive dry before testing the speaker and reinstalling.
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On larger speakers cut a ping-pong ball in half and do the same thing. The dome created thus will act as a return cushion and also act like a dome tweeter at higher frequencies improving the audio range of the speaker.
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Another Hint to improve the bass response in smaller speakers is to use an audio output transformer connecting the primary wires to 110Vac. Of course hook the secondaries to the speaker voice coil. The 60cycle hum will exercise the cone to create more travel (flex) in the speakers cone excursion. I would think 12 hours should be sufficient.
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Another thing is to use a small heated soldering iron to burn away some of paper edge to remove the edge stiffness. It should be equalized in to 4 quadrants to prevent the speaker from being misaligned. (I have not done this myself yet, but it sounds like a winner)

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PostSubject: Re: Hints and Kinks   2012-02-12, 12:05 pm

Another method for removing dust & debris from a speaker is to carefully brush the dust from the cone with a small brush or use VERY low pressure air. Remember that paper cones deteriorate over the years and heavy dust build up usually expedites this deterioration, so use extreme precautions so that you don't cause any further damage. Remove the voice coil cover (if you speaker has one). Place a towel or large rag on a flat surface and lay the speaker face down on it. Let the speaker play at a moderate volume overnight. This will allow the debris to gently vibrate out. Replace the coil cover as Cliff described.
If there are metal shavings around the voice coil, you can use a magnetized screwdrive to lift out the shavings. Be very careful that you don't puncture the speaker or damage the coil.
Dave
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PostSubject: Re: Hints and Kinks   2012-02-12, 1:26 pm

Very good advice I never thought of laying the speaker down trick. Thanks! Cool

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PostSubject: Re: Hints and Kinks   2012-02-13, 5:33 am

Learned that from an old NRI course. BTW here's a link to download a free and complete set of NRI course books.
4shared.com/file/niujJcwA/complete_nri.html

And a RCA repair course.
4shared.com rca_radio_repair_course_ocr.html

Dave
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Cliff Jones
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PostSubject: Re: Hints and Kinks   2012-02-13, 11:46 am

If you would like you can post those links in our Radio Related Links forum topic. Thanks

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PostSubject: Do you have a Scope and Tube-tester?   2012-02-13, 1:33 pm

Some of the older scopes were lacking in the calibration of settings for voltage.
However if you have a Tube tester you have a reference that is easily available. It has Filament voltages.
If you want to use them as a reference, just remember to do a little math. To calibrate the P-P voltage. If you need to read a 200 volt source and you don't have one. you can use the tube tester and set it on the 70 volt position for the filament. Multiply 70Vac ( actually 71.5 Vac-rms) by 2.8 to get 200 Vac P-P

If you don't have graticule's on the scope, then use a grease pencil and mark the screen so you have a mark at 0 inches and 4 inches, then make a mark at exactly 2 inches then between this center, mark 1 inch marks top and bottom of the center marks. These become your reference for full screen deflection boundaries of a a 200 volt P-P sine-wave. So if you need to check an ac voltage of less than 200 volts this will be your screen reference. When you set this up you only want the vertical gain set to make this adjustment. After this don't move the gain control. Make sure the horizontal adjustment is set at 0 (Zero).

So now reading the scope the lines represent (starting at the bottom line marked) 0volts then 50volts then 100volts then 150volts then the top mark represents 200volts (all as P-P voltages). So if you have a voltage half way between the 150 and 200volts you know it is 175V P-P.

Your tube tester is know a valuable ac voltage reference in comparison to buying an expensive AC reference voltage source. Now remember this isn't rocket science, this is for the poor man radio mechanic type person. So you can use the 5 volt filament as 14Volts P-P and 10Volts as 28.2 Volts P-P.
One of the reasons for using only the Vertical line and not using the horizontal gain is that without the horizontal you can see smaller spikes that exceed the voltage are more discernible on the faint peaks as the sweep doesn't steal some of the trace to see a whole screen which makes the vertical line more visible.

You can use the voltage divider in the scope to customise the voltage ranges to suit your needs of voltages.

Idea Idea You can use those to set up your reference voltage, also if you have an old tube tester you could tear it apart and save the filament transformer as a multi-voltage DC power-supply.

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