6-valve all-wave radio with spiral dial tuning.
The Stella model 38 'Aquila' used a diamond-shaped point of light to indicate the frequency, in a system probably called "Spotlight Spiral Dial" tuning (based on the wording of an advert from a Stella agent). Only one currently known cabinet design, which is a standard looking tombstone.
For more information on the model, see the Columbus version.
The diamond shaped point of light is generated by two aluminium discs with opposing spiral-shaped slots cut in them. They rotate independently of each other and in sync with the tuning gang in order to produce a hole where the two spirals meet that indicates the position of the tuning gang.
Intermediate Frequency: 456kc/s
Frequency Bands: 3
Chassis Notes(most schematics can be clicked to download a full size version)
Service information RCNZ_-_model_38_-_6V_AW_AC_-_1937.pdf
Take note regarding diode load resistor value:
3-band (all-wave) chassis covering broadcast (550 - 1500kHz), Intermediate SW (2.1 - 6MHz) and SW (6 - 18MHz).
The chassis uses a unique spiral dial tuning system with an effective tuning distance of over 2 feet and fast / slow tuning to provide fine control of the frequency. The dial assembly consists of either a red-tinted spiral line of light or a red dot (depending on brand) that indicates the frequency on a novel trio of spirals for the three bands. The band selector slightly rotates the system so that the dot or the end of the line aligns with the correct band.
The spiral tuning system is complex, and unless its been restored it always seems to be broken on sets found today. Repairing and setting the dial up takes some patience and trial & error, and while there is indication in the model 38 service documentation that there was to be a service bulletin from RCNZ for the dial assy, it has never been sighted.
Repair of the dial plates often requires the plates to be separated (on a lathe is easiest), then the old and normally torn / unglued paper to be removed and a new piece made. The red cellophane is often damaged as well and will most likely need replacing.
Note that the following images are from the rebuilding of the Pacific variant of the model 38, which used a line of light, not a diamond shaped spot. This was achieved with a leaf-shaped cutout on one plate rather than a curved line. Also note that one layer of cheap red cellophane (used here) is probably not enough and two layers would probably provide a better red shade - a thicker material like the colour gels used in stage lighting might provide better results as well.
Dial assembly split - new hand-cut black paper template shown top left
New paper and cellophane glued in place ready to reassemble
Dial plates rebuilt, showing operation
It appears like the original dials used chain, possibly to eliminate any chance of stretch and to ensure accuracy of the pointer - however nylon dial cord has been used successfully in recent repairs. The dial cord runs from the tab at the outside edge of the back of the plate around the pulley then around the central bakelite spiral pully (which should be free to spin on the shaft) 2½ times then to the arm on the wave-change switch which should be roughly 45º above horizontal from the shaft when switched to the middle band to give correct actuation - this will require experimentation. Ensure the dial cord sits in the right place on the central pully so it doesn't run off either end, and watch the spike that it seems to have - purpose unknown?
Dial cord and return spring shown in position
Dial assembly remounted and strung
Note use of an aligator clip to hold the cord in place while getting the length and position of the lever correct
Restoration of the dial assembly is a lengthy process, but well worth the effort.
General Construction Notes for Radio Corporation of New Zealand Ltd:
The first digit of the serial number typically indicates the year of manufacture of RCNZ chassis' (although not the decade - that requires a little knowledge of the valves, construction, etc). Sets from around 1934 onwards were often (but not always) constructed in a distinctive pressed 'baking pan' style chassis, seemingly unique to RCNZ.
Model codes beginning with a 0, for example the model 051, are Osram valve versions of the model without the leading 0. Technically the 0 should be an O (for Osram), however the digit 0 was used throughout the site before this fact was discovered.
The E suffix indicates a magic eye option is fitted (in models which were available with or without, such as the model 25).
A and B suffixes appear to be simply updates to the current model, R also appears to be simply an updated model ('R'edesign, perhaps?)
P indicates either a permanent magnet speaker version of a model which also came with an electromagnet speaker (the model 26 for example), or a portable model (like the model 694P).
N and M indicated miniature valve versions of a model which started with all (or a mix, ie: model 5) of larger valves. One of these two codes may indicate a transitional mixture of octal and miniature - clarification is required.
S often indicates a stereo model. It can also indicate 'self-biased' in the transition period between back-biased and self biased sets where there were models with both methods employed (53S for example)
Finally, other suffixes and prefixes make occasional appearances in the RCNZ lineup - like the 66W (a variant of the long-running model 66) and the 75XA (a 10-valve version of the model 75 with a separate amplifier chassis).
|1937||Columbus model 38 'Spiral Dial'|
|1937||Pacific model 38|
|1937||Courtenay model 38 'Opera'|