UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Chinese 1A2 Super Regenerative FM radio kit

Philips210 · 30th Dec 2018, 6:27 pm

Hi Mike.

I'm not really sure about the configuration of the 1A2 pentagrid valve but it seems a miracle it is able to work at broadcast VHF frequencies. So far though, I haven't been able to get to work above 102MHz and it was really struggling at that frequency. My experiments with the aerial found that about 48" was OK for the lower end of the band and about 18" for the upper end.

For the HT supply, I used my excellent 90V battery valve PSU https://www.vintage-radio.com/projec...y-set-psu.html

One thing that does need looking at is the operation of the 20k pot. There needs to be finer control over a more limited range. Also, the tuning capacitor would benefit from being an air-spaced type and a parallel low value variable cap for bandspreading and hence fine control. These would need to be fitted with longish spindles to mitigate hand capacitance effects.

One thing is for sure, there's no way the circuit will work as the supplied PCB has an error on the foil layout and the setting of the trimmer caps on the tuning cap need to be set up. I'm sure many people have been disappointed with this kit but it can work with a little bit of attention to the points mentioned. It's a pity there aren't any proper instructions with the kit. Also, I think the 1A2 valve as supplied is duff. It had corroded pins so wasn't a good sign. The heater is OK, maybe it has an impaired vacuum. I'll have to dust off my AVO VCM Mk3 and see what it says.

It's been an interesting little project and when time permits, I'm going to see if further improvements can be made.

Regards
Symon.

30th Dec 2018, 6:27 pm	#73
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,573	Re: Chinese 1A2 Super Regenerative FM radio kit Hi Mike. I'm not really sure about the configuration of the 1A2 pentagrid valve but it seems a miracle it is able to work at broadcast VHF frequencies. So far though, I haven't been able to get to work above 102MHz and it was really struggling at that frequency. My experiments with the aerial found that about 48" was OK for the lower end of the band and about 18" for the upper end. For the HT supply, I used my excellent 90V battery valve PSU https://www.vintage-radio.com/projec...y-set-psu.html One thing that does need looking at is the operation of the 20k pot. There needs to be finer control over a more limited range. Also, the tuning capacitor would benefit from being an air-spaced type and a parallel low value variable cap for bandspreading and hence fine control. These would need to be fitted with longish spindles to mitigate hand capacitance effects. One thing is for sure, there's no way the circuit will work as the supplied PCB has an error on the foil layout and the setting of the trimmer caps on the tuning cap need to be set up. I'm sure many people have been disappointed with this kit but it can work with a little bit of attention to the points mentioned. It's a pity there aren't any proper instructions with the kit. Also, I think the 1A2 valve as supplied is duff. It had corroded pins so wasn't a good sign. The heater is OK, maybe it has an impaired vacuum. I'll have to dust off my AVO VCM Mk3 and see what it says. It's been an interesting little project and when time permits, I'm going to see if further improvements can be made. Regards Symon.