23-07-2018, 01:35 PM
Thank you Trevor,
I built this up with my modules so a full circuit diagram, as such, does not really exist, but I attach photos showing the individual circuits. These are pretty much correct, although not showing the input tuned circuit. This is on the grid circuit, with a smaller winding for aerial connection. As in the photograph of the completed radio, the tuning capacitor has three sections, one for each RF amp.
The other tuning coils are not obvious. Following experience in replacing my hand wound heater choke inductance for my rod tubes, I started using those little (like resisistor colour band coded) inductors that can be bought. I tried them with oscillators and found them Ok. They were ideal for my miniature circuits with their low current operation. It just means they were not adjustable, and tapped inductance coupling would be messy. In more stringent applications a change of approach from the usual mutual inductance would be needed as well. The radio uses two of these. I do wind inductors. but bought ones are more predictable with tabulated data. I did wind the ferrite rod coils myself.
As I have mentioned elsewhere, I often don't go for minimalist circuits, although they can be far more efficient with all things considered. With a superhet I have a lot of thinking to do. There is the possibility of using rod pentodes (with the 1j37b as mixer etc), but do have a couple of ECH81's to hand as well. There are also thoughts of a double triode cathode coupled (Pullen) mixer and my mind even thinks to a double pentode balanced mixer that I see a skeleton of in one of my books (my mind wanders all over the place lol). I do have a couple of NOS double diode triode valves which would easily sort detection, agc and first audio. I do have some EF91's but, on test, they appear to be better at higher voltages than I generally use (although I am thinking of my usual 60V for early stages but 120V on output so the better voltage would be there). I need to do quite a bit of testing. Really things are in a big melting pot at the moment.
Tracy
I built this up with my modules so a full circuit diagram, as such, does not really exist, but I attach photos showing the individual circuits. These are pretty much correct, although not showing the input tuned circuit. This is on the grid circuit, with a smaller winding for aerial connection. As in the photograph of the completed radio, the tuning capacitor has three sections, one for each RF amp.
The other tuning coils are not obvious. Following experience in replacing my hand wound heater choke inductance for my rod tubes, I started using those little (like resisistor colour band coded) inductors that can be bought. I tried them with oscillators and found them Ok. They were ideal for my miniature circuits with their low current operation. It just means they were not adjustable, and tapped inductance coupling would be messy. In more stringent applications a change of approach from the usual mutual inductance would be needed as well. The radio uses two of these. I do wind inductors. but bought ones are more predictable with tabulated data. I did wind the ferrite rod coils myself.
As I have mentioned elsewhere, I often don't go for minimalist circuits, although they can be far more efficient with all things considered. With a superhet I have a lot of thinking to do. There is the possibility of using rod pentodes (with the 1j37b as mixer etc), but do have a couple of ECH81's to hand as well. There are also thoughts of a double triode cathode coupled (Pullen) mixer and my mind even thinks to a double pentode balanced mixer that I see a skeleton of in one of my books (my mind wanders all over the place lol). I do have a couple of NOS double diode triode valves which would easily sort detection, agc and first audio. I do have some EF91's but, on test, they appear to be better at higher voltages than I generally use (although I am thinking of my usual 60V for early stages but 120V on output so the better voltage would be there). I need to do quite a bit of testing. Really things are in a big melting pot at the moment.
Tracy
