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Old 20th Dec 2018, 1:24 am   #41
michamoo
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Default Re: More Chinese AM radio kits

A a circuit with a 500Hz multivibrator modulating a 455kHz ceramic oscillator.
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Old 20th Dec 2018, 11:26 am   #42
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Default Re: More Chinese AM radio kits

Earlier this year I designed and built this gadget to be the only tool required to properly align the Oscillator, IF & RF sections and also test the sensitivity of transistor radios. All the circuitry and mechanical construction is documented. I have not persuaded anyone to build it as a kit...yet, it is a bit time consuming to make as a one off.

http://worldphaco.com/uploads/The__H...nsanalyser.pdf
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Old 21st Dec 2018, 3:34 pm   #43
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Default Re: More Chinese AM radio kits

Four posts moved to a new thread: https://www.vintage-radio.net/forum/...d.php?t=152481
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Old 22nd Dec 2018, 12:10 pm   #44
Neil Purling
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Default Re: More Chinese AM radio kits

Thank you for moving the posts.

Back to the KX168: This is the last of the four I bought.
I discovered on assembly exactly as specified in the diagram that the audio stage has a feint hiss.
Sitting the PCB on top of a coil that was being injected with a 455Khz signal gave me a 1Khz tone from the speaker that I could peak up with B1 & B2.
I have no evidence that the local oscillator is running. It appears that I have made a mistake in wiring the coil. I will let you know if correcting it makes any difference
The wires are coloured red, blue & plain. The plain wire is the top end of the long winding. The red wire is connected to the negative track. Finally: The blue wire goes to the base of BG1 via C2. That blue wire is the connection between the two sections of L1.
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Old 22nd Dec 2018, 4:56 pm   #45
Neil Purling
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Default Re: More Chinese AM radio kits

Correcting the mistake did not make any difference.
I can inject a signal directly to the collector of BG1, (at very low level). Then I tune the cores for best sound level by observing the signal on the 'scope arriving at the top of the volume pot.
Has anyone made a KX168 kit?
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Old 23rd Dec 2018, 9:54 pm   #46
Neil Purling
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I should have said: "Made a KX168 that worked!. It just would not oscillate, not even when I swopped the black coil for a red one. I find it hard to believe the radio would ever work with the coils apparently in the wrong positions. Were you just lucky, or did you buy one ready-built? Yes, you can buy them ready made.
The KX168 was a vast disappointment, but the case has greater depth and uses a slightly larger diameter speaker. The PCB of the KX168 has different dimensions to that of the S66E and HX-6B, so you can't swop the boards and run the circuit from a CR123 battery.

There's another kit, called BSE818 that has a deeper case. It is still the six transistor type, but seems to have a push-pull o/p. The kit uses a pair of 'D' cells. That one also appears to have the odd order of coils. We'll see what happens when it arrives.
I am also awaiting a variant on the HX108-2 'long' superhet. The HX108-2A replaces the audio stages with a 8-pin 2822 IC.

Last edited by Neil Purling; 23rd Dec 2018 at 10:06 pm.
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Old 25th Dec 2018, 12:35 am   #47
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Default Re: More Chinese AM radio kits

I bit the bullet and ordered a ready-made KX1688.
I have wasted that much already on the dead ones.The ferrite coil connections were revised and agree with the diagram. It irritates me why I never heard a peep from any of the four I built. Why wouldn't the local osc run

I extracted the 9018H that was the mixer osc & tested it. It has a hfe of 115, which is close to the figure for other spare examples I tested. By contrast a 2N3904 gave an hfe of 321
It made me wonder about using one in the sole IF amplifier stage of an example of the six transistor kit type HX-6B or as the mixer/osc.

BTW: I just got a near-new Antex XS25 soldering iron, so I can't blame my tools in future.
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Old 25th Dec 2018, 8:56 am   #48
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Default Re: More Chinese AM radio kits

Quote:
Originally Posted by Argus25 View Post
Earlier this year I designed and built this gadget to be the only tool required to properly align the Oscillator, IF & RF sections and also test the sensitivity of transistor radios. All the circuitry and mechanical construction is documented. I have not persuaded anyone to build it as a kit...yet, it is a bit time consuming to make as a one off.

http://worldphaco.com/uploads/The__H...nsanalyser.pdf
Nice gadget, if you ever get any pcbs made I would buy one.

Peter
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Old 25th Dec 2018, 9:10 pm   #49
Neil Purling
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Default Re: More Chinese AM radio kits

If some other Forum members had attempted this kit with a similar lack of success then i'd know it isn't me being exceptionally cack-handed.
When I have 0 out of 4 kits work I wonder whether it is just me. I figure I wasted twelve UK pounds & that is enough to make this Yorkshireman very uncomfortable indeed.
Right now I am wondering about getting a shovel and upturning the dustbin to recover the other 3 corpses and learn something from my mistakes.

I measured the resistors before insertion in case there were any out of spec parts, but I don't have the means to do the same with the ceramic capacitors. Some of the odd values I do not have. In at least one attempt I used my own ceramic capacitors.
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Old 25th Dec 2018, 11:36 pm   #50
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Default Re: More Chinese AM radio kits

Hi

Yes, the worry is whether the components are out of spec. In the 1A2 radio thread, I found the 33uH RF chokes to be very low in value typically 20uH so wouldn't be surprised if other components are sub standard.

I would certainly build yourself or buy a decent capacitance meter if experimenting with radio circuits. My capacitance meters and ESR meters have paid for themselves time over. An inductance meter is equally useful when building radio circuits.

Regards
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Old 26th Dec 2018, 3:35 am   #51
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Default Re: More Chinese AM radio kits

I have just finished building another HX 108-2 but like its predecessor it won't work. Most of the supplied ceramic caps were out of spec, so I used my own as per the circuit diagram. There were no supplied 9018H transistors, so I used 2N3904 as substitutes. Similarly I used three 2N2222s to replace the supplied 2SC945s for the audio stages. All the resistors were within spec and the IF and audio transformers tested ok for continuity. I have no idea why the radio still won't work.
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Old 26th Dec 2018, 7:58 am   #52
Neil Purling
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Default Re: More Chinese AM radio kits

Did you try & inject a signal at 1Khz into the top of the volume control?
If you get signs of life from the audio stages then backtrack with a 465Khz signal along the IF strip. The IFT's may be far out of tune, such was the case with the working example of the S66E on my bedroom shelf.
You did bridge all of the test points with solder?
I made that mistake with the S66E as well.
They must be buying up QC reject components for these kits. Make a tuned circuit with them & it's never going to work. But total silence is mystifying when you used so many of your own parts.
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Old 26th Dec 2018, 1:04 pm   #53
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Default Re: More Chinese AM radio kits

I have just started assembling a xh108-2 kit and have completed the mixer oscillator stage. I am relieved to hear it radiate to anther radio. The oscillator coil was more purple than red in this kit. In any case the osc coil Always is the one without a capacitor underneath 😊
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Old 26th Dec 2018, 2:02 pm   #54
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Default Re: More Chinese AM radio kits

You have had more luck than me, congratulations.This is how the oscillator and IFT coils should look from above and underneath. Red, yellow, white and black is the sequence I used for my HX108-2.
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Old 26th Dec 2018, 3:34 pm   #55
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Default Re: More Chinese AM radio kits

I had a hx108-2 for xmas which I will have a go at soon, I recently did a hx-6b and I was surprised at how sensitive it was. Can anyone post a link to the KX168 to purchase one?
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Old 26th Dec 2018, 3:43 pm   #56
Jolly 7
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Default Re: More Chinese AM radio kits

Quote:
Originally Posted by Neil Purling View Post
You did bridge all of the test points with solder?
Hi
I have just finished measuring the current across all the test points which I had bridged.
They do look within the specified ranges. I have attached a diagram with my readings. The reverse of this page has the circuit diagram (not attached) but does not look correct to me e.g. T1 and T2 look funny and the fifth testpoint is not marked with a cross.
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Old 26th Dec 2018, 4:08 pm   #57
Neil Purling
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Default Re: More Chinese AM radio kits

Jolly 7: That photograph is just what is needed.
If any of us gets one of these KX168 kits, or indeed any other they can at least be sure of the oscillator coil & remember I was dubious about the black coil being the oscillator.
So... If the supplied coils in the KX168 all have the capacitor, then there's no way that the kit could work.

Also, that tuning coil could be incorrect.
On the KX168 the ferrite rod coil has a large and a small winding.
The coil has only three wires.
Look at the diagram for the HX-6B and for the KX168. I know the HX-6B does work.
It looks as though there is something very wrong with the front end of the KX168 and that could be why is does not oscillate.
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Old 26th Dec 2018, 4:27 pm   #58
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Default Re: More Chinese AM radio kits

My oscillator coil
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Old 26th Dec 2018, 4:49 pm   #59
Jolly 7
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And here is my HX108-2. I've bridged all the testpoints after taking current readings. Maybe I'll try a different 8 ohm speaker.
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Old 26th Dec 2018, 5:46 pm   #60
Neil Purling
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Default Re: More Chinese AM radio kits

Jolly 7: Regarding your HX108-2.
No 'hiss' from the speaker before you put a signal in when at full volume?
Then you get nothing from it by injecting signals.
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