Ekco B37, another TRF receiver.

[Geordie McBoyne]

Here's another 1930s TRF radio receiver, the Ekco B37. This simple receiver employs three pentode valves, VP2, SP2 and PM22D.  The set performs well with the usual ten feet of wire for the aerial, selectivity is good but not as good as any of the Philips Superinductance receivers.
The power supply unit is something I cobbled up twenty years ago.  The mains transformer was removed from a scrap video recorder.   The fluorescent display winding on the transformer supplies 40 volts to a voltage doubler circuit. Because the HT current consumption is only 10milliamps or so the peak putput from the doubler is about 120volts, the correct voltage for the B37.  Other windings supply the LT and grid bias.  The design of the B37 demands that the 9volt grid bias is supplied from an isolated source, unlike many other receivers where GB+ is connected to HT-.
The LT supply regulator is an LM317.

Geordie McBoyne.

[Old Sparky]

That P.S.U. is a good way to re-purpose parts from a scrap item, Geordie, and also a good way to power a vintage battery-operated radio. No doubt some would comment on the lack of originality caused by the addition of that power supply, but, if it does the job, to me, as I'm sure, to you, that's all that matters. The nearest I've ever got to that is adapting a mains transformer from a Grundig Valve radio to power a Telefunken set in which the original Mains and o/p trannys had fried due to failure of the selenium rectifier and inter-valve coupling caps.

[Geordie McBoyne]

I'm finishing off a power supplier for the Ekco B86.  Most of the of the original components of an Ekco AC12 have been retained, the mains transformer, smoothing choke, smoothing block etc, also modern components such as an LM317T to supply a reliable 2 volts for the valve heaters.  

I'll post pictures of the completed unit.

Geordie McBoyne.

[Murphyv310]

Hi.
These VCR Mains transformers are so useful for making up power supplies.
I've a few projects in my head and fancy making up a supply with variable outputs for battery valves and the Rod Pentodes.
Idea's are for 1 to 4 volts DC variable and fixed stabilised outputs, also stabilised HT of say 60, 90, 120 and 160v

[Geordie McBoyne]

Hi Trevor,
I've plenty VCR mains transformers here if you need any.
Best one in use is an ex-Fisher VCR transformer which has a 55volt winding, add this to another winding and supply this to the HT voltage doubler and over 180 volts is available. That's sufficient headroom voltage for the series regulator transistor to provide 160 volts for the Philco model 295 "farmhouse" radio. A 60 volt supply is provided for the screen grids of the 1A4E RF and IF tetrodes. A separate transformer and regulator supply the -3 and -9 volts grid bias.

Geordie McBoyne.