Sunday, May 31, 2009

Stereo quality amplifier

Late last year I started building a Wireless World Quality Amplifier.  The original design for this amplifier (mono) was published in 1934 and it became the reference British hi-fi amplifier - holding this position until the Williamson replaced it in 1947.

As my intention was always to create a useful working piece of equipment I was going to need a preamplifier suitable for use with modern sources - OK maybe LPs aren't considered modern any longer.

The solution was to build a stereo pre-amplifier to the 1950s Mullard design, but subsituting 1930s style octal valves for the 1950s 9 pin EF86s.  Plus I needed to add a phase splitter.   Six of the the excellent EF37A  made a quality pre-amp.  Now I just need to complete the cabinet.

Wednesday, May 13, 2009


Although computers were developed during (and slightly before) WWII, they weren't widely available. Most likely they weren't even capable of many of the things we use computer for today. But there are other ways of doing real time data processing and even simulations.
How about this -

Tuesday, May 12, 2009

Designed for repair II

Here's another example of a piece of test equipment designed for repair.

From gadgets
This is a painted brass plate from the rear of a signal generator. It shows the complete circuit diagram on the left and operating instructions on the right.   Of course it makes lots of assumptions - e.g. not everyone can read circuit diagrams,  and there were many perfectly good substitutes for the valves used.  The positions of valves are shown, but there's no indication of normal voltages to be found in the circuit - the easiest way of locating a fault.  Even so much better than is generally provided today.