Cameo SC70.

[Geordie McBoyne]

Introducing the Cameo SC70 four valve portable radio.    The SC70 was released in 1947 and was manufactured by Rees-Mace, London.  No connection with RM Electric of Gateshead.
Valve lineup is: all Mazda Octal 2volt filament types, TP25, VP23, HL23DD and Pen25.
Before the set is connected up to a 2volt filament supply and 90 volts HT a few simple tests will be carried out.  Can't risk destroying those difficult to find valves.

From the Valvepage:    http://www.thevalvepage.com/radios/reesm...o_sc70.htm

Geordie McBoyne.

[Murphyv310]

nice one.

[Geordie McBoyne]

Haven't power the set up yet but rest assured the set is almost ready to do so.
Replaced all the waxies, four TCC 0.1uF which includes the coupling capacitor between the anode of the HL23DD and the grid of the PEN45.  The three others are decoupling capacitors, one across the HT line, the common screen grid supply to the TP25 and VP23 and the AVC line smoother.   Found to be leaky was the 0.01uF DC blocking capacitor between the slider of the volume control and grid of the HL23DD audio amplifier.
The output transformer was replaced sometime in the distant past.  A RadioSpares component which judging by it's light green colour was made by Elstone Transformers.
Unusual for this range of valves the Cameo SC70 was designed to operated from a 90 volt HT battery.

Geordie McBoyne.

[Geordie McBoyne]

The Cameo SC70 is a worker. Only problems experience were around the frequency changer stage. The local oscillator was dead on both wavebands, 'scope was connected to the tuning capacitor, nothing. Tried another TP25, still no results. The oscillator coils checked out OK. Decided to give the wavechange switch a squirt of switch cleaner, that did the trick. Now the set is a good performer and gives full coverage across the medium waveband, 530Khz to 1600Khz. LW is OK. In terms of sensitivity the Cameo is as good as the Pye 65A and 69A battery receivers but audio quality and power output is nowhere as good as the Pye sets. The Cameo employs a single PEN45 output pentode whereas the Pye 65/69A have a push-pull output stage using the Mazda QP25 double pentode.
The Cameo operates from a 90 volt HT battery and according to the data for the PEN45 valve the power output is only 195mW. 400mW when the HT is 120V.

https://frank.pocnet.net/sheets/146/p/PEN25.pdfV.

The QP25 double pentode will deliver 450mW from a 90 volt HT supply. Almost 1 watt @ 120V.
https://frank.pocnet.net/sheets/146/q/QP25.pdf

Geordie McBoyne.

[Geordie McBoyne]

Correction: The Cameo employs a single PEN45 output pentode whereas the Pye 65/69A have a push-pull output stage using the Mazda QP25.
PEN45 should read PEN25.

[Murphyv310]

Hi.
I was wondering about the PEN45 to be fair and its use in a battery set.