30-10-2020, 05:37 PM
Hi.
Rather than hogging Amie's thread I thought I'd show this circuit remade into one of those Chinese kit radios.
Spurred on by Amie's thread I looked at the feasibility of cobbling the Philips radio on the Chinese PCB. As the component count is low it was easy to fit 3 transistors and a handful of components on the board.
Youll see in the photos how simple it is in comparison to the superhet kit.
Some observations with the reflexed circuit of the EE8 is that the reception is better with the antenna coil the opposite way round ie with the 5 turn pick up coil at the end of the bar. In the Philips circuit the HFC choke is damped with a 15k resistor, removing this increased output on both weak and strong signals, just snipped on my set. The 1N60P doesn't perform well in the way its wired in the original circuit but adding a reversed diode from its anode to ground makes a big difference to output again on all signal levels. Different diodes give different audio response, the OA79 is very good as is a unknown one that performs very well in a crystal set. Again the 1N60P is the worst with the resultant very toppy. The best combination is a 1N60P in place of the original OA79 and the unknown one in reverse with the OA79 a very good second place.
The other thing that made a big difference is a simple wire from the collector of the AF114 bent over the main tuning coil, moving it from half way of the coil to the pick up winding the reaction can be nicely controlled with boost at the LF end of the band when over the pick up coil.
A small slider knob will be made into the back cover for reaction adjustments.
As I've just set this up for headphones three transistors is extremely loud on my local and the other BBC stations from Westerglen, selectivity isn't too bad but its really sensitive when you adjust the feedback wire. Last night I received 5 foreign stations mainly Spanish and French, no sign of Caroline but I didn't receive it on any set. It out performs the proper Chinese superhet on the bottom of the band which is correctly aligned.
Nice bit of fun and a usable radio.
Rather than hogging Amie's thread I thought I'd show this circuit remade into one of those Chinese kit radios.
Spurred on by Amie's thread I looked at the feasibility of cobbling the Philips radio on the Chinese PCB. As the component count is low it was easy to fit 3 transistors and a handful of components on the board.
Youll see in the photos how simple it is in comparison to the superhet kit.
Some observations with the reflexed circuit of the EE8 is that the reception is better with the antenna coil the opposite way round ie with the 5 turn pick up coil at the end of the bar. In the Philips circuit the HFC choke is damped with a 15k resistor, removing this increased output on both weak and strong signals, just snipped on my set. The 1N60P doesn't perform well in the way its wired in the original circuit but adding a reversed diode from its anode to ground makes a big difference to output again on all signal levels. Different diodes give different audio response, the OA79 is very good as is a unknown one that performs very well in a crystal set. Again the 1N60P is the worst with the resultant very toppy. The best combination is a 1N60P in place of the original OA79 and the unknown one in reverse with the OA79 a very good second place.
The other thing that made a big difference is a simple wire from the collector of the AF114 bent over the main tuning coil, moving it from half way of the coil to the pick up winding the reaction can be nicely controlled with boost at the LF end of the band when over the pick up coil.
A small slider knob will be made into the back cover for reaction adjustments.
As I've just set this up for headphones three transistors is extremely loud on my local and the other BBC stations from Westerglen, selectivity isn't too bad but its really sensitive when you adjust the feedback wire. Last night I received 5 foreign stations mainly Spanish and French, no sign of Caroline but I didn't receive it on any set. It out performs the proper Chinese superhet on the bottom of the band which is correctly aligned.
Nice bit of fun and a usable radio.
