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May 2011

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Sun, 8 May 2011 18:09:10 +0300
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Sorry! Lapsus keyboardii! Of course, 995 Hz not kHz! It was not a MW 
transmitter!!!

Brian

On 08/05/2011 13:47, Brian Ellis wrote:
> Sorting out some old junk, I came across the first object I ever made
> with a transistor, dating back to 1955. In order to calibrate some
> telecomms gear in the field, I needed something portable. I made a
> couple of signal generators producing 0 dBm into 600 ohms at what was
> then 1 kc/s (now 1 kHz). These were 100 x 64 x 25 mm, including a 4.5 V
> "flat" battery. This was before PCBs (or even transistors) became
> mainstream, so the wiring was component to component. The transistor was
> a point-contact germanium type, made by a company in Newmarket, that
> cost a fortune, at the time (£20, if I remember correctly, half a
> graduate engineer's monthly salary!) and was so delicate that they
> failed if you looked at them hard. They had to be soldered in at the end
> of 30-50 mm leads with special short-circuiting heat sinks clipped to
> the wires. Looking at it, I was astounded at the appearance of the
> solder joints, somewhat corroded, but VERY ugly. Then I remembered the
> 100 W soldering irons we were using at the time, bare copper chisel bits
> from about 8 mm diameter stock, filed into shape several times per day.
> I thought it was a wonder I could solder anything so small with those
> tools. Of course, thermostats were not even thought of in those days.
> Temperature? Goodness knows, it was never measured, but I would
> guestimate close to 400°C.
>
> I know this device was used in several countries and my colleagues and I
> used them for several years. The brass case of the survivor is bashed
> and the paintwork reflects a hard life.
>
> I thought to myself that it was undoubtedly buggered. I couldn't find
> the right battery locally but asked my daughter to bring one out from
> Switzerland at her next visit. I could see the switch was physically
> broken, so I short-circuited it. I then reassembled it with the battery
> and found that IT WORKED! I made up a load of a 560 ohm + a 39 ohm
> resistors in series. Checking the output, it was amazing: 0.775 V RMS,
> spot on 0 dBm at 995 kHz!!!! Not bad after 56 years! Maybe rotten, ugly,
> uncontrolled, overheated, solder joints are not so unreliable as one
> would imagine!
>
> Brian
>
>
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