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-   -   More Chinese AM radio kits (https://www.vintage-radio.net/forum/showthread.php?t=152165)

Neil Purling 9th Dec 2018 11:43 pm

More Chinese AM radio kits
 
Has anyone bought a kit KX-168.? It has six transistors & runs off a single 'D' cell.
I did & I am sure that the supplied circuit diagram has some major mistakes. I haven't managed to get any sound further than a feint hiss. Injecting 455Khz by means of a coil of wire rested over the set's own tuning coils didn't yield a peep. I am sure that the Osc and IF components are given the wrong colour id for where they are in the circuit. That is based on the assumption that red means oscillator and the other two in order ought to be White and Black
This KX 168 diagram had them as Black,Red & White which agreed with an image of an a assembled board on the listing.
I am sure that there is something odd about the depiction of the AF stage too.
I bought several on the assumption I therefore had bits to spare & I have had zero joy, even when I used the Red, White Black sequence instead.:-[
I checked the values of the resistors as I assembled the radio for any that were out of tolerance, but could not do the same for the capacitors.
The above kit uses three 9018's as osc & IF, a 9014 as driver & a pair of 8050's as o/p pair. If it did work I wonder just how loud it would ever be with just 1.5V.
This KX 168 is one that you do not see on ebay or Aliexpress. They came via an intermediary from China internal market.

When looking at peoples assembly of the HX-6B kit I see a minor variation inside the case where the pair of AA cell are to the right of the speaker & are not above & below it.It just means that one way the cells are free to rock about and make the radio stop playing.
[Unless you pad the back of the case with toilet paper.]

MrBungle 9th Dec 2018 11:59 pm

Re: More Chinese AM radio kits
 
I never got the original ones with the 2xAA batteries working. The driver transistors got hot and nothing happened!

Jolly 7 10th Dec 2018 1:06 am

Re: More Chinese AM radio kits
 
Of the three different Chinese pocket radio kits that I assembled, the first one with MW and FM works fine. The second one, an HX108-2, never worked and the third, a ZX921, barely works but makes loud squealing noises.

I intend to try and make another HX108-2 in the coming weeks to see what might have gone wrong.

Jolly 7 10th Dec 2018 2:00 am

Re: More Chinese AM radio kits
 
In relation to the correct sequence of coils for the KX168, I too found that the black coil has been depicted as the oscillator at least on one website. This is very odd as the standard AM oscillator colour code should always be red afaik, even though there can be variations between red oscillator coils. I have never seen a red coil being used as the first IFT.
On my PCB and instructions, the oscillator coil was marked as 红 (Hóng), which is red in Chinese.

Neil Purling 10th Dec 2018 7:49 am

Re: More Chinese AM radio kits
 
I looked at a Web list of colours in Chinese to be sure about what wound component went where, but as I said I can't test capacitors to see if they are within 20%, or whatever tolerance they ought to have around their printed value.

I have done a HX-108 before with the same degree of success that member Jolly 7 had.
One of the KX-168 cooked the o/p 8050's. Dunno why, as in every instance I used long, thin-nosed pliers on the transistor legs as a heat-sink when soldering them in.
It makes me wonder about whether some of the parts are rejects or out of spec stuff that failed QC and therefore you have the odds stacked against you from the start.
The one that had the faint audio hiss wouldn't give a tone even when I injected the signal by physical connection. The black IFT usually has a broader peak than the white one. The cores are usually somewhere near to correct. Enough that you get the hiss of the mixer & IF strip even if you don't get stations. I triple-checked whether I had the ferrite rod coil's connections correctly wired as well. It makes me wonder whether the IF coils were junk.

Davewantsone 10th Dec 2018 10:24 am

Re: More Chinese AM radio kits
 
I have built around 3 of these Chinese radios. Two AM/FM using a ZN414 for the AM which only gave poor performance on the MW band. FM worked fine.
About 3 months ago I built a HX 108 and that works fine. The trouble is that all the instructions are in Chinese so I had to do some detective work to work out where the 4 tuning cans would go. The position for the cans is as follows looking at the component side of the board with tuning capacitor in top LHS the tuning cans form a square Top LHS Grey top RHS White Bottom LHS Green Bottom RHS yellow. Mine worked first time. The only problem is keeping the 1.5V cells in place!


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.

Neil Purling 10th Dec 2018 6:19 pm

Re: More Chinese AM radio kits
 
I forgot that on the HX 108 the can colours are slightly different. I would refer to Shango69's build of one on YouTube.
I was drooling over that tasty signal generator he has: Yum yum.
He took the HX 108, the HX-6B, with a tasty hot-rod Arvin transistor set for comparison on weak fringe signals to a abandoned mining settlement. I don't remember the name of the original video of the DX trip. There's bits tacked onto the constructional videos, but nothing of the HX-6B and HX 108 side by side.

Has anybody else here bought one of those KX-168 kits?
I won't say where from, since they are only a intermediary.

I thought that it must be my incompetence that is why I have had such a poor success rate with these kits. It is reassuring that I find others have had the same poor luck with them.

I assume that the AM-FM kit Davewantsone made was the Paensonic. I always found the AM side appalling. I assume it is due to the proximity of the copper-clad PCB affecting the Q of the coil because everything is squashed together. The case is somewhat like a Sony, the number of which I do not know.
The weird name is seems chosen to make you think of another major brand. The FM side does work, but the tuning is like balancing on a knife edge which is placed on the beam of a see-saw.

There are other AM-FM kits & they use a really fine-pitch IC you have to solder to the rear face of the PCB rather than it insert in a socket. It is at this stage I think i'd need a Antex soldering iron specifically for small work or needle-point bits for my 25W Weller iron. The IC does everything and there are few other bits apart from the coils for the AM IF strip. I don't know there is a discrete audio driver & o/p stage or not.

Is there anything people usually have good luck in making?

Restoration73 10th Dec 2018 7:58 pm

Re: More Chinese AM radio kits
 
You won't be unlucky with this one, aimed at the education market

https://www.elenco.com/product/amfm-...ic-transistor/

tri-comp 10th Dec 2018 10:09 pm

Re: More Chinese AM radio kits
 
1 Attachment(s)
Neil, I'm sure you already have this but it may give everyone here a better chance of helping out.
Good luck,

/Torben

Davewantsone 10th Dec 2018 10:23 pm

Re: More Chinese AM radio kits
 
Quote:

Originally Posted by Neil Purling (Post 1100100)
I assume that the AM-FM kit Davewantsone made was the Paensonic.

Yes the radio was a Paensonic. I used to use the Zn714 IC in my electronic classes when my students would build a radio with amplifier all powered from a 1.5V cell. The selectivity with the Zn714 was always poor even with a ferrite rod of around 6 inch length. The thing I liked was that the students could wind the aerial coils for both medium and long wave and just use a slide switch to change wavelengths. The amplifier was a class A output consisting of 3 BC107 (or BC547) driving a 8 ohm loudspeaker. (I got the circuit from Practical Wireless or Electronics sometime in the 1970's) When working the sound quality was good but not too loud which was an advantage when you had 20 students doing the same thing!

Neil Purling 11th Dec 2018 1:24 am

Re: More Chinese AM radio kits
 
tri-comp: Have you built one of those KX168? Did it work?
Three of four are duds. Even the one that had slight hiss from the audio stage was not passing IF strip noise, nor did it seem to have a running oscillator. It wouldn't pass a 455Khz tone.
Goodness knows why.

tri-comp 11th Dec 2018 7:53 am

Re: More Chinese AM radio kits
 
No, I haven't built this radio.
I've looked at the circuit and see one potential problem:
Compairing on-line datasheets for the 9018H transistor with the PCB legend I would suggest the transistor has reversed Collector/Emitter connections.
If the drawing of the components layout is shown topwise of course.
Much easier to see with the PCB in hand.
I suggest you check this out.
I haven't checked the other transistors but I wouldn't be surprised if they all have the same pin-out, i.e. all transistors are rotated 180-degrees out of order.

/Torben

Neil Purling 11th Dec 2018 8:46 am

Re: More Chinese AM radio kits
 
I believe that the printed sheet depicted in the PDF document shows the board from the print side.
You are right about the board leading one to insert the transistors incorrectly.

I still find the arrangement of the coil colours weird. I believe that is another mistake.
The circuit agrees with that of the HX-6B around the oscillator at least. The component values are different of course due to the differing supply voltage. On the KX168 diagram I still think they have made another mistake and L2 ought to be Red, B1 white and B2 Black.
Therefore the set would still never work if assembled as per the PDF document's images.
If that is the case it is inexcusable to leave such errors on the printed information.>:(

If I had cottoned onto this earlier I would have had at least two spare kits.:-[
The kits were dirt cheap, but I wasted time assembling them.

michamoo 11th Dec 2018 4:37 pm

Re: More Chinese AM radio kits
 
I bought the Paeansonic kit (Looks like the Sony ICF-40 ) radio a few months ago. I have built it and it does work but AM selectivity is rather poor and half the band is spoiled by hash. The FM side of things also works with good sound quality but tuning is rather sharp as has been said but also has an annoying mute that cuts in on anything much less than a full signal. Fm reception also seems overly affected by proximity of your hands while trying to tune.
Somebody suggested that the hash on AM was being generated within the FM sections which remain active even while switched to AM reception and could be cured by fitting a double pole switch. I still need to try doing that modification. I also hear it is possible to disable the FM mute but i need to look into that too.... Jon

Davewantsone 11th Dec 2018 10:00 pm

Re: More Chinese AM radio kits
 
The HX 108 out of interest only uses a supply of 1.3V (2 slicon diodes via a resistor to drop the 3V supply) for the RF and IF stages. It is only the driver and output transistors that get the 3V. I removed a 1.5V cell and shorted the connections so the radio only got 1.5V. To my surprise it worked quite well with a good amount of volume!
Out of interest I pad the radio with the circuit diagram sheet!

Neil Purling 12th Dec 2018 1:19 am

Re: More Chinese AM radio kits
 
I have got a HX108, not yet assembled of course.
There is also a HX108-2A. It has an 8 pin IC in it, the function of which I suggest is for the entire audio stage as there are only four discrete transistors in it. Naturally I had to have one.

Neil Purling 12th Dec 2018 10:19 am

Re: More Chinese AM radio kits
 
What are the near equivalents to the 8050 output transistors in the KX168?
I am just wondering in case I assembled the last kit & or any others KX168 I may buy & they got 'cooked'.

I would have thought that power o/p isn't going to be beyond 0.2W in a feeble thing like the KX168.
Because it has only 1.5V max supply voltage. You wouldn't expect 'loud', without the sound being awful in a thin cased thing like this.

Guest 12th Dec 2018 3:45 pm

Re: More Chinese AM radio kits
 
Quote:

What are the near equivalents to the 8050 output transistors in the KX168?
I would say anything the right way round (NPN PNP) in a similar package.

MrBungle 12th Dec 2018 4:52 pm

Re: More Chinese AM radio kits
 
S8050's are pretty hefty little transistors. 2N4401 gets my vote although Ic(max) is much lower.

Some of the cheaper Chinese transistors are pretty good.

Neil Purling 12th Dec 2018 5:20 pm

Re: More Chinese AM radio kits
 
I am determined to make that last KX168 and have it work. The way the coil colours are marked seems to be totally wrong for it to stand any chance of functioning if you make the radio as the sheet says.


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