Quote:
Originally Posted by Hengist
The output stage is in the style of a late 50s / early 60s hybrid valve/transistor car radio.
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Wow, that is a really creative and interesting looking radio with lots of attention to detail. I have never seen a radio built like that, it is very impressive.
I have always been totally enamored with the hybrid car radio style audio design. Part of this is that the input impedance to the grid of the driver valve (typically an EF98) can be 10 meg ohms, and the class A output stage can drive a 4 ohm speaker, that is a huge impedance transformation, from just the two devices aided by the transformers despite the base current hungry output transistor.
I liked the hybrid and 12V HT valve idea so much I once built one, using an OC16 as the output stage. The only snag I found was that the ECH83's triode wasn't too good over 12MHz, so I had to abandon it for the L/O and use an MPF102 for the 5.7 to 18.2 MHz short wave band. The coils were hand wound, except the Miller IF cans.
Its also fun to work on "12V valve gear" where you don't get zapped! There is a photo of the superhet radio I made here:
http://worldphaco.com/uploads/THE_EF98-OC16_RADIO.pdf