Quote:
Originally Posted by Ed_Dinning
Hi James, looking good
Lots of Mil stuff (1154/55) used this trick to provide a bias voltage, often had a cap across the resistor for smoothing.
Connecting HT - to chassis can cause all sorts of problems and damage valves etc.
Cheers, Ed
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Hi Ed
The big capacitor in the design is that very cap - it's even mentioned in the AP.
I've met another stumbling block in testing the main receiver. The same resistors are in fact housed in the Pilots Control unit. I only have the later version of this unit where they removed the Glide function (coming in on a fixed field strength line). The original unit switched between AGC and no AGC the new unit doesn't! Thus the bias resistors have disappeared from that unit and this explains why the later receivers connected all the cathodes to 'Earth'. Also all the pot values changed!
In the attached pics you can see that the pots are really very different from what you might expect. With no chance of finding any other such a device I decided that I might be able to 're-stuff' the existing odd pots. So I fiddled about trying to open then up and to my surprise and delight found that the pots consist of a casing and inside a perfectly normal pot! My cunning plan is now a more conventional re-stuff!!
I suspect that as the pot thread has a sort of rubber seal then this casing is intended to seal the pot from the effects of water/damp. A sort of waterproof casing.
Now I have to stop work on the main receiver and restore the control unit - again bringing it back to the 'A' version! Well almost anyway.
Cheers
James