Having followed this thread with interest, I decided to take up the challenge and order a HX108-2 kit. Once the kit arrived my first action was to test every component and record the various measurements.
The doubtful components were the capacitors as others have found – the electrolytics all had ESR’s which were a little high, and the disc ceramics were out of spec, even applying the worst case tolerance of +80% -20%. I sourced suitable replacements from my stock.
The supplied transistors were 4x 9018G and 3x9013H, so no 9018H for V3, V4 and V5, again something which others seemed to have experienced. However the gain figure for the transistors was within that specified, so I decided to use them in the kit, using the highest gain 9018G for V1, and close matched 9013H's for the output pair V6 and V7. The diodes are all 1N4148 as supplied, and tested ok.
The oscillator and IF transformers all showed continuity and reasonable inductance measurements, and the Chinese letters on the schematic translated as B2 – Red, B3 – Yellow, B4 – White, and B5 – Black.
All resistors supplied were within the ±5% tolerance.
The audio transformers were identified as Driver – Green, and Output – Yellow, and primary and secondary windings checked for continuity – both measured ok.
The kit went together well and once completed was powered and tested with a DMM across the five bridging points. All measurements agreed with the values shown on the schematic. The bridging points were then soldered with a wire link, and everything assembled into the case.
Switch-on resulted in a speaker hiss and tuning brought in a few stations. The frequency was a little high against the tuning scale, but adjustment of the ferrite rod antenna/coupling coil position, trimmer capacitors and oscillator transformer corrected that. The IF transformers were peaked for maximum audio output. I was surprised by the level of audio output - given a 3 volt supply voltage, and the sound quality was very acceptable from the tiny loudspeaker. Altogether very pleasing for a £5 investment.
