Hello All,
I can understand two separate transistors for mixer/oscillator in a Superhet radio. But how does one transistor do the job of two? If this is true then why were two triodes or a pentagrid converter required years ago? Why wasn't it done with one triode in AM Broadcast band radios? With tubes, due to the higher frequency of FM two tubes worked much much better than the combined pentagrid converter.
But transistors work at higher frequencies. Please explain the single transistor circuit to me, or please let me know where I can find an article about it online somewhere.

Thanks,

Dave

It's an interesting question that I didn't know either.. so I goggled around and here's what I found.

Basic bipolar transistor mixer circuit - signal applied to different transistor electrodes

It is this transistor mixer circuit that forms the basis of many circuits within transistor radios using discrete transistors. Often a self oscillating mixer is used, where a single transistor circuit based around this configuration acts as an oscillator and mixer.

Self oscillating bipolar transistor mixer circuit
as used in a typical discrete component transistor radio

More info can be found here:
http://www.radio-electronics.com/info/rf-technology-design/mixers/bjt-transistor-mixer-multiplier.php

Dave,
From memory, think it's called an "Autodyne Converter". Try Googling that.

marv

:Hello All,
: I can understand two separate transistors for mixer/oscillator in a Superhet radio. But how does one transistor do the job of two? If this is true then why were two triodes or a pentagrid converter required years ago? Why wasn't it done with one triode in AM Broadcast band radios? With tubes, due to the higher frequency of FM two tubes worked much much better than the combined pentagrid converter.
: But transistors work at higher frequencies. Please explain the single transistor circuit to me, or please let me know where I can find an article about it online somewhere.
:
:Thanks,
:
:Dave
: