Among first steps of almost any radio restoration projects is to dismantle the unit, both to ease deeper cleaning and to gain access to the circuit for visual inspection and - later on - for realignment and calibration. So I did. Attached below please find a collection of pictures showing the internals of my new old Panasonic DR-22 (refer to Part 1 for some more background on this story).
The solder side of the main board with the front panel controls exposed
The nice old-style mechanics of the tuning scale
The component side of main board with the tuning capacitor well exposed
Luckily, it seems that the unit does not have suffered from any major fault or repair in its past life. Internally it appeared fairly clean and in good order. After having removed the five self-evident screws on the back panel (only one of them is "hidden" inside the battery compartment) and the knobs on the front panel (all but the main tuning knob), both panels can be easily separated from the main circuit board so exposing that nice piece of vintage electronics.
It is very good for us experimenters that the whip antenna, the battery compartment and the loudspeaker can be easily disconnected from the main board without having to use a soldering iron. The radio itself can still stand up without the front and back panels and it can be very easily serviced this way, with a minimum risk of causing mechanical damages. Well done, old Panasonic designers!
The back panel dismounted with connections for antenna and batteries
Unfortunately while separating the front panel from the main board, a piece of plastic detached from around the signal meter (circled in yellow in image below). The other small rectangular piece of black gummy plastic silently dropped from inside the radio while detaching the back panel. I couldn't find out where it came from. I hope to discover its original placement while rebuilding the set.
Now I'm waiting for a stick of the renowned CAIG DeoxIT D100L conctact cleaner and another stick of DeoxIT Fader F5 for potentiometers. After having recovered a good behaviour of switches and pots I will proceed with a realignment. Stay tuned for more RF-2200 restoration adventures!
The rear of the front panel with the loudspeaker
The timestamp above says (I suppose) December 24, 1977
The venerable front panel dismounted and ready for a careful cleaning
Some time ago I wanted to buy a vintage portable receiver for trying a bit of MW listening with good performances even without the need of external antennas or the complexities of software defined radio (SDR). I went through the web and read a number of reviews and finally I choose to look for a used Panasonic RF-2200. I liked its look very much and felt it was just the kind of radio I was looking for. I found one on eBay in fairly good conditions and at a reasonable price (compared to how much these sets are usually rated). Also important it was that that National Panasonic DR-22 (also known as RF-2200BS) came from Europe, without the additional costs for shipment and long processing time at customs that affect similar purchases from the U.S.. Being targeted for the european marked, the DR-22 was also equipped with an AC mains selector (220V/50Hz or 110V/60Hz) so it can be used in Italy (where I live) without the need of an additional AC-AC transformer.
Here below a photograph of the set as it was depicted on eBay:
When the radio arrived in my hands, I quickly tested it to find out if it was fully functional, what of course was partially unexpected, given the age of the receiver. While it looked fairly goon on FM (where it was possible to receive many strong signals from local broadcast stations), apparently it was almost deaf on medium wave and shortwave bands. I knew a common problem with these sets is bad contacts in front panel switches and potentiometers due to long inactivity, dirt and oxidation. So I tried to operate them a bit and something started to come out of the speaker. Well, at least it seemed that there were no major faults. The short video below shows these initial tests:
OK, even after having verified that (apparently) the unit didn't suffer from major issues, it was still apparent that MW sensitivity was quite low and the same it was in SW. Probably a realignment was needed to improve the overall performamce. Also, the switches and potentiometers required a deeper and more durable cleanup. The service manual was available in digital format from the web. It was to time to plan a restoration. More on next episodes of my RF-2200 restoration adventures.
Dopo mesi e mesi di lavoro, dedicandovi spezzoni di tempo a distanza anche di parecchi giorni uno dall'altro, finalmente ho deciso di considerare completata la costruzione del mio ricevitore a reazione.
Scrivo volutamente che "ho deciso" di dichiarare finita la costruzione, perchè in realtà sarebbe possibile apportarvi ancora diverse modifiche e fare ancora prove, probabilmente una lista molto lunga di possibili sperimentazioni. Ma sono giunto all'esaurimento delle energie e del tempo che ero disposto a dedicare a questa esperienza, per cui eccomi qua con queste note conclusive, a mostrarvi un paio di foto del ricevitore "finito" e un piccolo filmato di una prova appena fatta in tarda serata sulle onde medie.
Particolare interessante: il ricevitore, per come è stato costruito, coprirebbe la gamma di frequenze da circa 1300 kHz a circa 3700 kHz. Per portarlo più in basso, nel pieno delle onde medie, ho sfruttato un suggerimento di Bernd (non conosco il cognome) della lista regenrx di Yahoo: ho inserito un paio di bacchette di ferrite all'interno del supporto della bobina di sintonia e oplà, ottenuto il miracolo senza nemmeno dover accendere il saldatore.
La qualità delle foto non è buona, perchè sono state scattate al chiuso, di sera e senza l'uso del flash.
Lo schema del pannello frontale è quello riportato nel disegno qui sotto.
Nella seconda fotografia si vede anche l'alimentatore costruito per fornire tensione ai filamenti ed alle placche delle valvole del ricevitore.
Nel filmato ho cercato di evidenziare anche il leggero effetto passabasso di un filtro audio L/C passivo, che può essere inserito tramite il piccolo deviatore posto tra la manopola che controlla la reazione e quella che controlla il volume. Il deviatore ha tre posizioni: filtro inserito, filtro escluso e "mute" (che è la posizione centrale).
Nel mio piccolo, sottoscrivo e riprendo l'appello che il buon Andrea Lawendel ha lanciato dal suo blog Radiopassioni - in nome della ragionevolezza e della comune passione per la radio:
