FRG-7 - REPLACING LIGHTBULBS
The procedure is illustrated in pictures 1 to 9 above:
1. Removing the cover - 9 screws
2. Unscrew the panels, prise back the drum assembly...
3. ... and withdraw the panel of bulbs
4. The bulb panel assembly
5. With a rubber cap removed...
6. ... and the bulb illuminated
7. Unscrew the brackets for the main dial bulbs...
8. ... and lift a bracket clear with its bulb
9. Be sure to protect the tuning dial against damage when soldering. I used card and Sellotape
Preselector + 'MHz':
The panel holding the Preselector + 'MHz' bulbs unscrews from the top and can be eased, very gently, out of the drums. Soldering is then necessary.
The main dial bulbs can be withdrawn from beneath, and again require soldering.
The Preselector + 'MHz' bulbs are wire-ended types and were probably specified as 40 or 50mA at 12V, but they work at about 35mA 8.5V in the preselect and even less in the MHz positions due to the series resistors R13, 14. At this reduced current, they should last for ages.
They are covered in little rubber caps, and to fit in the caps, the replacements need to be 4mm diameter, sometimes known as 'T1¼' size, though without the caps any dia. up to 5.5mm could be used. I recommend that all four preselector bulbs be replaced in order to assure equal brightness.
The main dial bulbs were metal-cap pre-wired types, presumably rated at 12V 40-50mA, as they draw about 40mA at 10.5V. The bulb was 5mm Ø, and in order to fit the grommets which support them, I recommend replacement with LES 14V 50mA types, with the original wires soldered to the new bases.
WHITE LED REPLACEMENT
In the Yahoo FRG-7 Group Rob gives advice (Dec.2005) on replacing the dial bulbs with LEDs:
"Don't go for the 'super bright' LEDS, as they have a narrow focus for the light beam (you really want the light from the sides of the LEDS). You need the 2000/3000 mcd LEDS, and these will fit in the bulb slots in the MHZ and preselector drums - in fact, in the MHZ drum there is already a dropper resistor for the lamps - simply change this to about 560 ohms and replace the bulbs with LEDS while observing the polarity.
"If you are looking for the dropper resistor for the front lamp (the main tuning dial illumintation) it is on a small tag-strip mounted on the chassis behind and to the left of the tuning capacitor.
"5MM leds fit well throughout. I am also considering adding an extra LED to illuminated the S-meter.
"Overall this has been a successfull project. Only one thing may need refinement, the gel covers for the original lamps will not cover a 5mm led, and as a result here are some (barely noticeable) 'hot spots' of illumination on the dials (3mm LEDS however will fit inside them - this might be a option if this concerns you)"
Dimensional details of the main TUNING KNOB
JH - May 2016