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The Collection

November 8, 2011

The collection as of 4/14:
Please DO click on each picture, they display so much better…..
RFS Scope Collection 4:21 Main Bench
The wooden box on the wall at the right contains a 3KW isolation transformer with variac and ammeter. This increases safety at the bench and allows me to bring things up slowly whilst keeping an eye on the current draw. The size of the transformer allows me to run many items of test gear while working on a project, I do sometimes have two 500 series scopes on at the same time.
Note that the Bush radio is not the ubiquitous DAC90 but the quite rare AC91. This one was made in 1947. The differences are that the AC91 has an auto-former in place of a dropper resistor for the heater chain and a short wave band in addition to the long and medium wave bands. The auto-former is a far superior solution that dissipates much less heat which may be why the back is still in place! It also permitted me to set it up for operation on 120V by a simple tap change. Here is the schematic:

I have posted on the use of this radio with a two-valve am micro-transmitter here:
RFS Scope Collection Side Bench 4:14
RFS Scope Collection 4:14, Carts
RFS Scope Collection Corner
RFS Scope Collection Early Tek & HP
RFS Scope Collection Main

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4 Comments
  1. David Taylor permalink

    Amazing collection – interesting to see that a Bush DAC90A Bakelite radio c1950 has found a place on the shelves – they seem to get everywhere!!

    • Hi David.
      Thanks, I am glad you enjoyed it. The Bush radio is not as common as it appears, this one is an AC91 and it has an auto-transformer rather than a dropper resistor and could be set up for use here in the US simply by changing the line tap position on the transformer. The auto transformer may be one reason why it still has the original back, much less heat! It also sports a short-wave band in addition to the standard medium and long wave-bands.
      Richard Sears

      • David Taylor permalink

        Far better with an auto-transformer – much less heat dissipated than with a dropper!

        Have a great year in 2012 Richard!!

  2. mike permalink

    Ive a dac 90a which im going to convert, with a bush auto transformer from another chassis. I now know the connections. thanks!

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