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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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2nd Dec 2020, 7:47 pm | #21 |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Starting to think that the tuning cap is trying to pull the LO to low and its stalling hence the noise,
Messed about peaking it up and its a sensitive little radio when compared to some other radios i have
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2nd Dec 2020, 8:42 pm | #22 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,063
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Re: HX108-2 AM radio kit problem
In my radio, I did not use any of the supplied 223 ceramic disc caps as most were way out of spec. Maybe the ones in the RF section are suspect and causing some sort of tracking mismatch/ instability ? I would try substituting those. Also the newer HX108-2 kits seem to have different tuning caps compared to the set I built.
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2nd Dec 2020, 9:03 pm | #23 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Quote:
The lowest marking on the dial is 530khz , But you can go lower as the tuning cap still has a bit of play in it before it end stops, Which makes me think the LO is being pulled to low hence the noise. P.S The tracking is pretty much spot on Jay
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Help!! I've been electrocuted by a glass thing that glows Last edited by Radio Scotland; 2nd Dec 2020 at 9:10 pm. Reason: more info |
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2nd Dec 2020, 9:31 pm | #24 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: HX108-2 AM radio kit problem
Looking at the schematic shown upthread, I note the absence of a padding-capacitor - which would im[ply to me that the tuning-capacitor would need to have different angle:capacitance profiles for the 2 sections.
In days-gone-past there was a Jackson Bros. tuning capacitor with one set of vanes giving 208pF the other set 176pF just for this reson. You say you substituted a different capacitor - do you know if this had the right angle:capacitance profile for both the ferrite-rod signal-frequency stage and the local-oscillator? If it's not tracking properly, you could find either the LO or the ferrite-rod end up tuned perilously close to the IF [or its 2nd harmonic] at which point interesting things are likely to happen. |
2nd Dec 2020, 9:46 pm | #25 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Quote:
Cheers Jay
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Help!! I've been electrocuted by a glass thing that glows Last edited by Radio Scotland; 2nd Dec 2020 at 9:48 pm. Reason: extra info |
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9th Dec 2020, 10:04 pm | #26 |
Dekatron
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,422
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Re: HX108-2 AM radio kit problem
These all suffer with the same issue. I've made two and no matter what I've tried the problem persists. I think it's down to the PCB layout or the IF bandwidth is too wide in addition to the higher IF frequency. Fortunately only Spirit Radio on 549Khz is the only station that's readable here in Scotland just comes through with no instability but only just. I think you will have to live with it TBH.
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10th Dec 2020, 12:05 am | #27 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: HX108-2 AM radio kit problem
Parasitic oscillations.
David
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11th Dec 2020, 10:01 pm | #28 |
Tetrode
Join Date: May 2013
Location: Enniscorthy, County Wexford, Ireland.
Posts: 74
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Re: HX108-2 AM radio kit problem
100 nf across electrolytic between power rails ei7ka.
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15th Dec 2020, 6:30 pm | #29 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Quote:
I'll try the 100nf cap as suggested and report back, Cheers Jay
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15th Dec 2020, 10:03 pm | #30 | ||
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,063
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Re: HX108-2 AM radio kit problem
Quote:
Can you receive Algeria on 531 kHz and Kossuth radio Hungary on 540 kHz on your set ? Mine can and both stations are very strong right now. It's just after 9 PM. |
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15th Dec 2020, 10:14 pm | #31 | |||
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Quote:
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16th Dec 2020, 6:02 pm | #32 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,586
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Re: HX108-2 AM radio kit problem
I note on the diagram in #6 that the first transistor has an 'G' suffix while all the others have 'H' suffixes. Is this actually carried through into the kit contents, do you get one 'G' and the rest 'H' or are they all just the same type?
If none of them are marked differently to the others there is likely to be some variance in the hfe values for each, so maybe just try swapping the first transistor for one or two of the others to see if that makes a difference? |
16th Dec 2020, 6:55 pm | #33 | |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,063
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Re: HX108-2 AM radio kit problem
Quote:
The more recent kits may now be supplied with 9018Hs. |
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16th Dec 2020, 6:56 pm | #34 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Quote:
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Help!! I've been electrocuted by a glass thing that glows |
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28th Dec 2020, 10:51 pm | #35 |
Diode
Join Date: Dec 2020
Location: Lasi, Romania.
Posts: 3
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Re: HX108-2 AM radio kit problem
My HX-108 have same motorboat oscillation problem....it is very sensitive but the audio is low quality..
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1st Jan 2021, 4:14 pm | #36 |
Nonode
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,087
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Re: HX108-2 AM radio kit problem
Is the thing over-sensitive or is the PCB badly designed?
I was just wondering if it would be stable if the same radio components were built up on strip-board instead. They still sound appalling. Maybe they also need better driver & output transformers as well as well-matched output transistors? |
7th Jan 2021, 11:48 am | #37 |
Dekatron
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,422
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Re: HX108-2 AM radio kit problem
Hi.
I think for the price and the purpose of these kits as a learning aid, we really cannot be too critical. Many years ago we had the likes of the excellent Philips EE8/20, amongst others. These days learning aids like this have all but gone, the Chinese Kits are not ideal as there is no explanation as to the circuit nor decent construction details but they are better than the zero learning aids made in the UK. They do work but not what we expect as more experienced hobbyists. So I don't think we should be so critical of them.
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7th Jan 2021, 2:39 pm | #38 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
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Re: HX108-2 AM radio kit problem
I have made a couple of these kits and spent some time 'playing' with them. I also have aligned them with an RF signal generator. In addition, a couple of friends have also made them.
So, my thoughts are they really are excellent little kits. I did the usual recommendation and tested all the parts prior to building, and one of mine has really excellent performance. (apart from the obvious audio limitation of a tiny speaker) It easily out performs my Tecsun radio for pulling in stations and is great fun for DXing. I have received more stations with this set than many others. However - what I have found is that the supplied transistors vary considerably with performance. It has been suggested in the past that they may be 'rejects' and I would tend to agree. One of my friends builds just wouldn't work at all; no amount of messing and checking could get it to oscillate properly. After swapping out the oscillator/mixer transistor it burst into life, despite the original testing OK. I have put a number of the supplied transistors on my Peak semiconductor analyser and found considerable variations - hfe that vary from 18 to 265, leakage currents which vary between 0 and 0.7mA, and B-E voltage drops varying between 0.45 & 0.9V Clearly not ideal when trying to get a set to work! I would suggest swapping at least the oscillator transistor and maybe the 1st IF one and see if that helps. |
15th Feb 2021, 10:57 pm | #39 |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: HX108-2 AM radio kit problem
Just a quick update on this, I haven't had a chance to work on the radio since posting this thread, But i recently dug out the first one i built and it doesn't have the same problem, (Could have sworn it did) Although it does have the mandatory scratchy tuning cap
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17th Feb 2021, 1:10 am | #40 |
Nonode
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,087
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Re: HX108-2 AM radio kit problem
Can you actually get a better quality tuning capacitor & what values should be used?
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