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Old 27th Dec 2018, 12:17 am   #61
Jolly 7
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Default Re: More Chinese AM radio kits

There is no hiss from the speaker at all after bridging back the test points. I would wonder what purpose the test points really serve if the radio fails to work in spite of the correct current readings across all five of them
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Old 27th Dec 2018, 7:25 am   #62
Neil Purling
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Default Re: More Chinese AM radio kits

I would like to ask any other Forum readers: Can you see the oscillator waveform on the emitter of the first transistor as well as trying the test with another radio?
Just wondering if we can help member Jolly 7 and I can file the information for future reference.

Jolly 7: What test gear do you have? If you have a signal generator, does it output at audio frequencies as well as RF?
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Old 27th Dec 2018, 8:57 am   #63
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I have a Heathkit RF-1U. I know how to get RF out of it, but not sure if I need RF or AF to test the audio stages of my radio and what dial knob settings to use if AF is required. There is an AF out socket and the RF out socket too. Please advise. I have also asked this question under the vintage test gear thread.
P.S. I don't have an oscilloscope yet.

Last edited by Jolly 7; 27th Dec 2018 at 9:07 am.
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Old 27th Dec 2018, 11:24 am   #64
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Default Re: More Chinese AM radio kits

Like I have said before my HX102 works perfectly and apart from slight adjustment of the tuning preset caps no further alignment was needed. I enclose scans of the circuit and a scan of the radio. In my previous posts the chinese translation clearly state the osc coil is black!
All you need to do to check if the amplifier is working is turn the volume control to maximum and touch the wiper with a uninsulated screwdriver you should hear a 50Hz hum out of the speaker which will vary if you turn the volume control.
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Last edited by Davewantsone; 27th Dec 2018 at 11:42 am.
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Old 27th Dec 2018, 12:44 pm   #65
Jolly 7
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Default Re: More Chinese AM radio kits

Ian and Graham, thanks for your guidance with the correct settings for my RF-1U signal generator. I heard no output from the radio after connecting the test probes to the centre of the volume control pot and the earth of the PCB. Just to verify that my signal generator is working, I connected it directly to the speaker and could hear a tone.
This therefore makes me think if one or both of the audio output transformers could be faulty. I did test the audio preamp and output 2N2222 transistors before soldering them in and they were fine.
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Old 27th Dec 2018, 8:07 pm   #66
Neil Purling
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Default Re: More Chinese AM radio kits

Dave: Regarding the driver & o/p transformers. Does the diagram suggest which goes where? I assume that the windings of each are wrapped in different coloured tape and maybe a resistance test would show which is which as well.
I was just wondering if Jolly 7 got them in the wrong position.
Jolly 7: Have you tried poking around the IF strip from stage to stage with 465Khz to see how far the signal gets along the chain?
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Old 27th Dec 2018, 8:34 pm   #67
Jolly 7
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Extremely happy to report that my HX108-2 is finally up and running. The problem was the yellow output transformer and it happened to be only one of two components I didn't meter before soldering. When I desoldered and measured it, the secondary coil read 6 megaohms !!

Luckily I had a spare kit and used the output transformer from there. The correct reading for the secondary of the output transformer should only be 2 ohms.

Here is the final transistor lineup:
V1: 9018G
V2: 2N3904
V3: 2N3904
V4: 2N3904
V5: 2SC945
V6: 2SC945
V7: 2SC945

I used better quality electrolytic and ceramic capacitors but did not change any values.
A big thank you to everyone who helped me with this project, which I was almost going to bin. I will attempt to align it at a later time as I can hear many stations without.
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Old 27th Dec 2018, 8:43 pm   #68
Jolly 7
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Default Re: More Chinese AM radio kits

Should it also be of interest, the primary coil of the output transformer has a resistance of 11 ohms. The readings between the centre tap and either end of the winding should be 5 to 6 ohms.
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Old 27th Dec 2018, 9:44 pm   #69
Davewantsone
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Default Re: More Chinese AM radio kits

In my earlier post(number 7) I listed the colour of the various components for the circuit diagram that I had for the HX108-02
I have just looked at the circuit diagram and
B1 is the ferrite aerial coil
B2 is the black/grey can
B3 is the white can
B4 is the yellow can
B5 is the green can.
B6 is the green audio driver transformer
B7 is the Red audio output transformer.

Hope this helps.[/I][/I]
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Old 27th Dec 2018, 10:09 pm   #70
Jolly 7
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Default Re: More Chinese AM radio kits

There are obviously more than one version of the HX 108-2 in circulation. B1 in mine is similar to Dave's but my B2, B3 and B4 are yellow, white and black respectively. My audio driver transformer B6 is green, but my output transformer B7 is yellow.
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Old 27th Dec 2018, 10:17 pm   #71
Davewantsone
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It seems this must be the case with different colours for the various components.
My circuit diagram does state in Chinese the colours as I listed above.
Do the other HX108-2 use the same diagram as mine and what do they say the colours are for the various cans and transformers?
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Old 27th Dec 2018, 10:39 pm   #72
Jolly 7
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Here is the component layout for mine. The colours are in Chinese but I deciphered them and are as stated in my previous post. e.g. the oscillator coil is Hong i.e. red.
Another point of note is that Dave's oscillator and IFT cans appear to be smaller than my version. I bought all three of my kits in 2018.
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Old 27th Dec 2018, 11:15 pm   #73
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Default Re: More Chinese AM radio kits

What a shame so many of these very affordable Chinese radios don't work, or take fairly detailed electronics knowledge to get going.

They should be an ideal source of encouragement to young electronics enthusiasts. But how many keen youngsters have become disillusioned, disappointed and put off the whole electronics field, because they or some well-meaning friend bought something that turns out to be complete c**p. It was possibly excusable in the early days of transistors, but not in 2018 for goodness sake.

It doesn't exactly inspire confidence does it?

Ian
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Old 28th Dec 2018, 7:59 pm   #74
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I have started my assembly of the HX108-2 around the front end & I have been gratified to hear it heterodyne with the oscillator of a Benkson 323 adjacent to it exactly as samoca58 did.
So now I am going to assemble the rest of the IF strip to the detector.
There are differences in the arrangement of the coils: In mine it is red, yellow, white, black. The red & yellow are rather dull but you can tell perfectly well what they are.
The printed sheet is dated 2018.8.6, which I take to mean 8th June 2018.
Their Web site link works. Be careful to add the .cn on the end or you get a hard-core porn site.
The zxradio.com.cn site is not in English & I don't know if there are English pages.

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Old 29th Dec 2018, 10:46 am   #75
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Default Re: More Chinese AM radio kits

Thankfully Jolly 7 sorted their HX108 out.
The member also told me that they didn't get the higher gain 9018H transistors to go in the IF strip. Thus the use of the 2N3904.
I was just wondering if the 2N3904 would serve as a mixer/osc as well?
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Old 29th Dec 2018, 5:06 pm   #76
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Default Re: More Chinese AM radio kits

After reading this thread I purchased a couple of HX 108_2 kits. These arrived very quickly and I built one today. I have built similar radios from scratch in the past so was fairly confident it would work. The kit came with 4 X 9018G transistors and 3 different ones. Upon assembly the kit worked first time but was very insensitive and audio output was low. The If transformers we quiet well aligned already and I proceed to align the oscillator and aerial tuned circuits. This is were I discovered the problem the aerial tuned circuit sidi not appear to be any where near resonance. I will take a look at it later.

Dave
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Old 29th Dec 2018, 7:14 pm   #77
Neil Purling
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In the set of components there are three diodes. D1 & D2 are 1N4148. The other one is in the o/p stage. On my diagram D3 is given as 1N4118, which would be a Zener diode. However I was supplied with three 1N4148. If that is an error, then it was not the only one in the components. For C3 I ought to have had a 0.01uf but there were only 0.022uf & I looked at every single disc ceramic capacitor in case I missed it. I used one of my own stock.
Goodness knows if there have been revisions from the diagram. I don't read whatever Chinese language the leaflet is printed in.
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Old 29th Dec 2018, 7:21 pm   #78
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All my diodes are 1N4148s and the 608 ohm resistor is a 680 ohm, I assumed it was a typo. I had one ceramic capacitor that I couldn't read assumed that was the 0.01uF. I was impressed with the quality of the PCB .

Dave
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Old 29th Dec 2018, 7:32 pm   #79
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All my diodes were IN4148s too. I used my own ceramic caps including a 0.22 uF tropical fish one.
I also used all electrolytic caps of my own. An electronics engineer once advised me to use the same value but largest possible electrolytic capacitor that fits. And use low ESR ones too where possible.
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Old 29th Dec 2018, 8:58 pm   #80
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Default Re: More Chinese AM radio kits

My 108-2 kit has 3x 1n4148. D3 is a typo on the circuit diagram. C3 is 10n on the cct diagram and I actually had a 10n supplied. Looks physically the same as the 22n types supplied but has 103 marked on it. I doubt it's that critical.
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