Battery Radio Power Supply

[bobhowe]

Hi would it be possible to start a separate section for power supplies for battery radios as especially some radios have a multi voltage supplies . It would be a good to discuss how members have made them kind regards Bob

[boater sam]

It is very easy to assemble batteries to replicate the original types that will no longer be available using 9v or button cell stacks for HT and cylindrical cells for LT and GB.

[Doodlebug]

It so happens that 9 volt batteries can usefully plug into each other
in series!
In this way a plugged in stack of say 12 will give you 108 volts.
Be careful though, because if you plug in just over 20 batteries you have
a lethal supply which can kill !

[Ed_Dinning]

Hi Bob, see David about the use of old video mains transformers. I can let you have some circuits on my return.
I've also developed a small transformer a bit bigger than an OPT that can be used for modern battery sets (90V + 1.5 or 7.5V)

Ed

[bobhowe]

Hi Ed Thanks for the offer of circuits David has spoke to me about using a transformer from a VCR and he has built a power unit for his Philco 296 Farm Radio Set. I have seen a 90V 100W DC converter I will pm you the link . kind regards Bob

[Geordie McBoyne]

The Philco 295 battery radio receiver was designed to perform as well as a mains radio. To achieve this the HT voltage is 160V. The push-pull output stage employs a Brimar type 2103, a very rare valve in the UK. https://www.radiomuseum.org/tubes/tube_2103.html
I got lucky finding the ex-Fisher-Sanyo video recorder mains transformer which has a display driver secondary of 55volts, this added to other windings and a voltage doubler realised an output of near 180volts. A TIP49 transistor is employed as the series regulator to supply the 160volts for the output valve.
The same transformer supplies through an LM317 the 2volt filament supply. Another winding is used for the grid bias which is -3volts for the audio amplifier and -9volts for the 2103 double pentode output valve. Another LM317 regulates the grid bias.
The screen grids of the 1A4E RF and IF tetrodes a supplied with 60volts derived from the main HT line.

Geordie McBoyne.

[bobhowe]

Hi David good use of the VCR transformer some of these sets with multi voltages must have been expensive for batteries in they day never mind now makes sense in making a mains powered supply nice Philco 295 would have been top quality in its day kind regards Bob

[Geordie McBoyne]

The Ekco B37 receiver employs a battery eliminator which was intended for the much larger Ekco B86 superhet receiver. However, it was found the the 2volt filament supply which was derived from the charger winding on the original mains transformer was not capable of delivering the 1.25Amps demanded by the valves and dial lamp in the B86.
Filament current greedy TP22 frequency changer, VP210 IF amplifier, L21DD detector and audio amplifier and QPP valve type QP230.
The B37 is a simple three valve TRF receiver. Valves are Mullard VP2, SP2 and PM22A.

Geordie McBoyne.

[bobhowe]

Hi David I remember you showing me the Ekco B37and battery eliminator both of them performed very well kind regards Bob

[Geordie McBoyne]

Hi Bob,
despite being a simple TRF receiver the Ekco B37 has remarkable selectivity. Works well with the usual ten feet of wire as the aerial.
The power unit I'm using with this set has a separate mains transformer for the grid bias. The transformer can be replaced with one having two 9volt secondaries.
Then it will be possible to use the power unit with larger radio receivers such as the Ekco B86.

Geordie McBoyne.