Quote:
Originally Posted by turretslug
I'm encouraged by the interest in the DF section too- I gather that it was an innovative and effective design at the time, so it's good to see it appreciated! Shame that magic eyes generally are an endangered species though.
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Its a general observation that amateurs have taken equipment and imposed on it their own set of requirements, with zero interest in the history or original purpose of the equipment. Hence the general ripping out of the DF section - if not all the components - then at least the valves, apparently to save heater and HT current.
A proper appreciation of vintage equipment, in my view, is to first understand why the equipment was designed and produced - and to get a grasp on that original requirement. Then try and return the equipment to as near original as possible, and see how well it fulfilled that requirement.
Given that we are talking about power supplies for the R1155 in this thread, I've always found it remarkable that the original supplies were pretty basic affairs - either hefty rotary converters or huge great mains power supply units, with large metal rectifiers and very heavy multiple choke smoothing.
Interestingly there isn't a stabiliser anywhere in sight. Certainly not in the power units, and not in the set either. So one can get away with a very basic power unit - for modern purposes, a simple transformer, full-wave or bridge rectifier, followed by resistance/capacitance smoothing is good enough for the 210V HT rail. As far as I recall the HT current doesn't vary very much as the R1155 is used, so there won't be large variations in HT voltage. And that in turn will reflect on the local oscillator being "stable enough".
That's further helped by the IF being some 4.5kc/s wide at -6dB points, with no fancy features like a crystal filter to demand a highly stable LO. No idea how good the set was on CW, but the matching transmitter, the T1154, chirps like mad on CW. With a transmitter that bad, why bother stabilising the receiver?!
Richard