ferguson: Ferguson (USA) model 12

Hello,

       I own a Ferguson - 12, but I do not know if it is the old or the new one. I have unmounted it from the case for drawing schematic and doing some minor repairs.
    It has 3 AF stages. The coupling between 1-2 and 2-3 are RC. The coupling between detector and 1st AF is by a transformer of the brand “Silver - Marshall”. Because the shape of transformer mounting and  connections I think it could not to be the original.
    In addition, I need some information about DC supply:
     The are four +B sources ( detector plate, RF , AF(1-2) stages and power stage. May be 22.5 for detector, 135 for power and ¿ what for AF and RF ?
    There is -C for grid returns of the 3 AF stages, the same for all three, two of them 201A and the last one of 112A type. For both tubes -C would be -9 volts if +B were 135. But 201A and 112A have a diferent DC wire.

    The reostat  is only conected to the RF amplifier (2 tubes). Then, all other tubes should work at battery voltage ( 6 or more volts) ?
    Finally, I suppose that -B is connected to ground. Ins this case, if +A battery is connected to -B, the grid return of AF would be to +A, not usual, I think. The grid of detector tube returns also to +A, but it is a 200A, and for this also seems to be wrong.

     I will be thankful for much any information or suggestion on this subject.

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Ferguson radios are quite rare and I don't know of another 12, but your questions can only be answered definitively by looking at another one.  I have uploaded the schematic of a model 8 to the relevant page, which should be visible after it has been approved.  Although the two models are very different mechanically, they are probably similar electrically.  

Your description makes me think your set has been modified.  You are correct in questioning the battery connections, as they don't make sense.  Also 1926 is fairly early for a resistance-coupled circuit.  It's very unlikely that Ferguson used a 200A detector tube.  There is no published description of a 12, but the model 10 used 01As, with an optional 112A output tube.

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Hello Alan,

    Thank you for your answer. I own your 3 valuable volumes about Radio Manufactures 1920's. It is one of may favorites readings. Congratulations.

    I am waiting that  schematic of 8 modell is available to decide on some connections to the power supply. For now I have replaced transformer (coupling detector - first AF) because it was open. I found an old Thordarson, probably of a similar time. Best regards.

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