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Old 3rd Mar 2016, 11:34 am   #94
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: HMV 653 Broadcaster all wave.

RE: Working out wattage etc, there are various ways, it's all down to the info that can be gleaned from the manual (or actual measurements) If the voltage developed across the resistor is known then that voltage squared divided by the resistance will give the power dissipated, as will determining the current through the resistor then multiplying that current by the voltage developed across the resistor, as will squaring the current flowing through the resistor and multiplying that current by the resistance.

In the case of R3 & R7 no voltage difference information is given in the manual but the current is given so in that case the quickest way to determine the power dissipated is to square the current then multiply by the resistance.....So now we've gone through the three methods of arriving at a result (power) with the information that's been available, all basic stuff but well worth remembering.

Soldering wires etc neatly is down to practice, for removing wires components etc I use a desoldering pump, desoldering wick, usual tools etc in whatever combination, for doing screened cable strip off the outer insulation to whatever length is required and unpick the braid, twist the braid tight but not tight where it contacts the inner insulation, the solder tag(s) should be well prepared, they need to be clean and tinned, some folks tin the braid and the inner conductor some don't, I never do unless it's old stock stuff that's oxidized, prepare the inner conductor, feed the ends of the braid and inner conductor through the solder tags by about 3 mm or so then bend them over and under, make sure everything's sitting proper and not under strain and that nothing's going to pop off, that way both hands will be free during the soldering operation, a quick solder with a hot iron and the jobs done.

The characteristic impedance of the cable (75 ohm or whatever) will make no difference in this case. The characteristic impedance of a cable is given in ohms but it can't be measured with a ohmmeter, for audio use the main parameter, signal wise, is the cables capacitance per meter but only on longer runs where the source impedance is high, the lack of voltage rating for the screened cable wouldn't affect anything in this case.

For RF work things can change, transmission line is a whole different subject in that respect, but if you are interested then the following video is well worth watching:

https://www.youtube.com/watch?v=I9m2w4DgeVk

As is this:

https://www.youtube.com/watch?v=DovunOxlY1k

Both are classics.

This post might cross.

Lawrence.
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