A selection of old Radio Equipment

Sunday 19 October 2014

Practical Wireless August 1964, Transistor Tuner/Converter

 Practical Wireless Transistor Tuner/Converter

 
The Transistor Tuner/Converter described in the August 1964 issue was a one, two or up to five transistor frequency converter




It was in effect the front end of a normal radio set, with a traditional Denco Blue coil front end RF tuned circuit , tuned by VC1 


This fed a to the Base of the first OC171 (Tr1) and amplified and the signal appeared at the collector
and tuned again the the Denco Yellow coil with VC2

the output of this yellow coil is fed to base of the next OC171 (Tr2)
If you note Tr2 is also wired with a third Denco coil this time a white oscillator wired in a Self oscillating mixer circuit

Here's a clue, instead if changing the base current to make the transistor oscillate, The Output from the collector is fed back to the emitter to change that 




This mixer oscillator OC171 (Tr2) runs at 1.6 Mhz and the base of this transistor is fed with the received signal the frequency the converter is tuned to, the two mix and hey presto the out put appears

this can be fed directly to a Medium wave radio tuned to the converters output

As with all mixers a number of other mix frequencies appear at the out put car has to be used to tune the Medium wave radio to the correct one 


One set back of this set is the coils fitted were 3T range about 1.6Mhz to 5.5Mhz to cover the Long wave all the way to 10 mtrs the builder needed to purchase 5 ranges of coils and it cost a lot of money.


N.B
Denco made two types of Oscillator a White 1.6Mhs +- and Red 465Khz to run with each coil set
except there was no specifically made 1.6 Mhz Osc coil for the lower 1T range 



Denco made a range of IF transformers again for 1.6Mhs +- and 465Khz 

yes after changing a OC171 (leaky ) to a spare AF116 I had it works well 
now part of my collection




Sunday 12 October 2014

Practical Wireless November 1960, Pocket Superhet

Practical Wireless Pocket Superhet 


The PW Pocket Superhet described in the November 1960 issue was a 6 transistor and 1 diode pocket transistor radio designed for medium and long wave reception

Using germanium transistors through out, the OC44 in the front end was really pushing the technology with a

Transition frequency (ft),  8 MHz: 
a Forward current transfer ratio (hFE), min: 100
Maximum collector-emitter voltage (Uce), V= 12

as usual for the time period one slight mistake and the device was ruined and at 28/- each, that's 28 shillings or £1.40 in decimal currency, which would equal £28 each in today's money, so failure of a device would be a financial disaster.

Click here to see how poor the GB £'s value actually is now


Semi conductor line up
OC44 RF & Oscillator/mixer
OC45 1st IF
OC45 2nd IF
OA81 Demodulator & AGC
OC71 Audio driver
2 x OC72 Push pull Audio O/P
                                                                Power = PP4  9volt battery
                                                             Speaker 2 1/2" Celestion 3 ohm

I regularly use this site for Transistor Data


I am fairly lucky my dad sent off to Practical wireless for the case, seen here
and started buying the parts each week what actually happened is lost in time
but he never made it.





I have been left a mint case and a Circuit diagram supplied by an old friend
who's dad did make his 

                                                                     The Blue Print


I have all the parts to build mine

the Question now is

Shall I