UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Reply
 
Thread Tools
Old 29th Dec 2018, 11:22 pm   #81
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

I am in the process of building my second HX108-2. The ceramic capacitor marked 103 measured 10 nF on my component tester, so that was fine, but two samples of the ones marked 223 measured 40 to 42 nF. Not sure how critical that is but as per the circuit diagram they are out of spec and I won't be using them.
Jolly 7 is offline   Reply With Quote
Old 30th Dec 2018, 8:52 am   #82
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

I suppose that you are checking everything after the grief the last one gave you?
Will you be using the supplied transistors or the 2N3904?
You said the radio performed especially well.
Neil Purling is offline   Reply With Quote
Old 30th Dec 2018, 9:20 am   #83
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

For V1 through to V4, I will be using 2N3904s. The second kit didn't come with any sort of AF transistor, so I will be using S8050s from my own stock and if they work, might experiment with some AC127s to see if they work too. It was nice to buy some of the latter from a shop recently while abroad.
I may run out of the 223 caps but have ordered some more.
Jolly 7 is offline   Reply With Quote
Old 30th Dec 2018, 3:01 pm   #84
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

In the diagram the driver & o/p pair are specified as 9013H.
I was supplied with a trio of 2SC945G. Before I fitted them I wanted to know whether they are a good match to the specified type. They test as having a hfe of 230, 263 and 264 on my DMM.

Last edited by Neil Purling; 30th Dec 2018 at 3:13 pm.
Neil Purling is offline   Reply With Quote
Old 30th Dec 2018, 11:53 pm   #85
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

In my radio V1 through 4 are 2N3904.
V5 is a 2SC495G, the one with the highest hfe.
V6 & 7 are a pair of 9013 taken from another kit that had a hfe of 250 & 251 respectively.
Upon switching on it was barely audible, but then I got out my signal generator and gently tweaked the white, yellow & black cores to a peak by ear at 460-465 Khz.
Then I was seeing if I could get a broadcast & I have!
It needs more fiddling I suppose.
I really want to get it into the case & try some speakers to see if there's one that sounds any better than the one supplied with the kit.
Neil Purling is offline   Reply With Quote
Old 1st Jan 2019, 12:09 pm   #86
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

When Shango066 made the HX-6B he also took it to the abandoned mining site, his low-signal test site.
I wonder how he could tell what he was listening to going by the camcorder's sound pickup.

I was just wondering if you used the 2N3904 in the HX-6B in place of any 9018 it would increase the performance.
Is there anything that you can do in order to introduce some 'top-cut' to a transistor radio?
In a valve radio I would put a capacitor between the anode of the o/p device and chassis of around 0.01uf.
Neil Purling is offline   Reply With Quote
Old 1st Jan 2019, 2:13 pm   #87
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

There is something not quite right with the audio preamp and output stages of the HX 108-2. My first one has stopped working. It will only give scratchy sounds and no tone when the middle of the volume pot is connected to the AF out of my signal generator. I changed all output transistors, but no luck so far.

I could verify that the RF section is working by bringing it close to a second radio, where from I could hear a beat frequency. Maybe one of the output transformers are internally shorting or something ?
Jolly 7 is offline   Reply With Quote
Old 1st Jan 2019, 4:28 pm   #88
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

I suspect poor quality control of the audio driver and output transformers, green B6 and yellow B7 respectively in HX 108-2. For one sample I tested, which worked for a while, B6 had a 230 ohm primary but the second sample only 175 ohm. The secondaries of the two samples I tested were also in wide variation of each other.
In relation to B7, for which I found a defect in one of my samples referred to in an earlier post, the correct reading for the primary would appear to be 12 ohms with a centre tap of approximately 6 ohms. The secondary should be in the region of 2 ohms.

This is a question in relation to the matching of the audio output transformer and the supplied speaker. Is a 2 ohm audio output transformer a good choice for an 8 ohm speaker ?

Last edited by Jolly 7; 1st Jan 2019 at 4:34 pm.
Jolly 7 is offline   Reply With Quote
Old 1st Jan 2019, 7:16 pm   #89
Davewantsone
Pentode
 
Join Date: Dec 2011
Location: Wigan, Greater Manchester, UK.
Posts: 133
Default Re: More Chinese AM radio kits

When using an ohmeter you are only measuring the D.C. resistance of the coil or winding. The coil will have an "ac" impedance "Z" which will consist or R and XL the inductive reactance which will vary with the frequency of the output voltage. for both the transformer and the speaker!
Davewantsone is offline   Reply With Quote
Old 1st Jan 2019, 10:08 pm   #90
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

I decided to isolate the audio output transistors and transformers from the circuit board to try and find the fault. For this purpose, I used a homebrew mono amplifier that runs on a 9V battery. My guess was right and the radio works and tunes fine as it should using my external amp. I might use the board to make a larger superhet or maybe transplant it into a non-working desktop radio. It should be easy enough to make wired connections for a larger tuning cap and volume control pot.
Attached Thumbnails
Click image for larger version

Name:	IMG_20190101_194835.jpg
Views:	79
Size:	103.0 KB
ID:	175556   Click image for larger version

Name:	IMG_20190101_195034.jpg
Views:	74
Size:	92.9 KB
ID:	175557   Click image for larger version

Name:	IMG_20190101_194953.jpg
Views:	60
Size:	62.7 KB
ID:	175558  
Jolly 7 is offline   Reply With Quote
Old 2nd Jan 2019, 12:11 am   #91
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

Maybe you can get better alternatives to the driver & o/p transformers?
Eagle LT44 and LT700 I believe, or clones of same. The problems you have had only confirm my suspicion that the kits are made up from QC reject parts. How else could you get one of these kits for less than six pounds delivered to your door?

Did you find the board to be a tight fit in the case?
The side of the board looks like it isn't going to fit in w/o fouling the moulded posts for the battery terminals. I am being very wary about how much force I use, like it is going to explode shards everywhere.
Neil Purling is offline   Reply With Quote
Old 2nd Jan 2019, 12:23 am   #92
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

I did have a look at miniature audio output transformers on ebay, so might purchase them at some point.
The board is indeed a very tight fit. I was pulling the cabinet with my left hand and trying to push the PCB in with my right. One of the tabs got marred but the other one held the PCB in place. I didn't try to fit the battery terminal in place as I was using a temporary double AA battery clip.
One of the other annoying problems I had was with one of the IF transformers. When I was adjusting it (using proper tools), the core slipped quite a bit down in the can. I was ultimately able to bring it back up carefully to where it should be, but was afraid it might break.

Last edited by Jolly 7; 2nd Jan 2019 at 12:37 am.
Jolly 7 is offline   Reply With Quote
Old 2nd Jan 2019, 9:43 am   #93
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

Jolly 7: I had that happen to me with the IF can. As a result I am very careful with the adjustments now.
I use a cut down & filed plastic knitting needle, which is non-conductive & non-inductive.
Neil Purling is offline   Reply With Quote
Old 2nd Jan 2019, 8:14 pm   #94
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

When those ceramic capacitors are in tuned circuits I guess it would be wise to substitute your own. People do exactly that. You don't need much error when the component is of a low value to mess up the oscillator.
Neil Purling is offline   Reply With Quote
Old 2nd Jan 2019, 10:11 pm   #95
Philips210
Octode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 1,510
Default Re: More Chinese AM radio kits

Hi

I bought two of the HX108-2 kits at different times and have just had a look through the contents.

There are subtle differences on the circuit diagrams, not in the actual circuit, but rather in the additional information.
In kit 1, the kit is described as HX108-2 on both sides of the sheet. The IF and oscillator transformers have the normal bold colours (see pic 1). The driver transformer is coloured green and the output transformer is coloured yellow.

In kit 2, the kit is described as 108-2 on the circuit diagram side of the sheet and XH108-2 on the board layout side of the sheet. (note the transposed X and H). The IF and oscillator transformer colours are more pallid (see pic 2). The oscillator transformer could be mistaken for being brown in colour.
Again, the driver transformer is green and the output transformer is yellow. (see pic 3)
My aerial coil has suffered some impact damage and may be unusable in this kit.
Maybe kit 2 is a copy of kit 1 by a different supplier.

These kits seem very good value considering what you get for your money including the carriage. When I get time, I'll have a go at building them.

Regards
Symon
Attached Thumbnails
Click image for larger version

Name:	IMGP7675.jpg
Views:	50
Size:	78.5 KB
ID:	175653   Click image for larger version

Name:	IMGP7676.jpg
Views:	48
Size:	78.2 KB
ID:	175654   Click image for larger version

Name:	IMGP7679.jpg
Views:	41
Size:	65.5 KB
ID:	175655  
Philips210 is offline   Reply With Quote
Old 2nd Jan 2019, 10:19 pm   #96
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

@Symon: when you get a moment, do you mind posting the resistance readings of the primary and secondary windings of the green and yellow audio transformers. I just wanted to compare them with mine. Thanks
Jolly 7 is offline   Reply With Quote
Old 2nd Jan 2019, 11:31 pm   #97
Philips210
Octode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 1,510
Default Re: More Chinese AM radio kits

Hi Jolly 7

I've just checked the resistance of driver and output transformers in both kits and have attached the readings in the pic below.

I was quite surprised to see there is considerable variation between the transformers in both kits. I don't know which set is considered to be as expected but going by the pallid IF transformers in kit 2, then I might be inclined to trust the readings in kit 1 as opposed to kit 2.

In the garage, I have some Eagle LT44 driver and LT700 output transformers. I'll check the coil resistances sometime tomorrow. These are physically larger than the ones in the HX108-2 kits though.

Regards
Symon.
Attached Thumbnails
Click image for larger version

Name:	hx108-2 tx res001.jpg
Views:	62
Size:	96.8 KB
ID:	175677  

Last edited by Philips210; 2nd Jan 2019 at 11:47 pm.
Philips210 is offline   Reply With Quote
Old 2nd Jan 2019, 11:54 pm   #98
Jolly 7
Hexode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 393
Default Re: More Chinese AM radio kits

Thanks Symon. Much appreciated. My readings for the green driver transformers are broadly in line with yours for the two samples I tested. However, I had a yellow output transformer which had a secondary in the megaohms range and didn't work at all. The replacement yellow transformer, which worked for a while, has a secondary coil of 2 ohms (primary 11 ohms, 5+6). This has now given up on me, as you may have gathered from my previous posts.

Please let us know if you decide to use your Eagle transformers instead of the kit ones. I was also wondering what would be the acceptable resistance readings for the radio to work without breaking down.

Last edited by Jolly 7; 3rd Jan 2019 at 12:02 am.
Jolly 7 is offline   Reply With Quote
Old 3rd Jan 2019, 2:28 pm   #99
samoca58
Triode
 
Join Date: Sep 2014
Location: Ringwood, Hampshire, UK.
Posts: 17
Default Re: More Chinese AM radio kits

I wonder how this speaker from one of my 108-2 kit passed QC. The dome is way off centre...
The picture is not taken from an angle.
Admittedly I haven't connected it up yet.!
Attached Thumbnails
Click image for larger version

Name:	IMG_20190103_132201.jpg
Views:	64
Size:	71.3 KB
ID:	175717  
samoca58 is offline   Reply With Quote
Old 3rd Jan 2019, 4:39 pm   #100
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,966
Default Re: More Chinese AM radio kits

Don't expect miracles. Wonky vegetables may be perfectly OK, but not wonky speakers.

I have encased my radio. The PCB went into the slots with no problems. I have not used the OEM speaker... At this point I must give a big thank you to Forum member 60 oldjohn who, very generously gave me a little Elac speaker of just over 2" in diameter. There are never any clamps. The usual method is hot-snot. I had to get creative with the back of the case to accommodate the magnet bell.
Attached Thumbnails
Click image for larger version

Name:	HX108-2 a sml.jpg
Views:	64
Size:	50.5 KB
ID:	175733   Click image for larger version

Name:	HX108-2 b sml.jpg
Views:	61
Size:	55.0 KB
ID:	175735  
Neil Purling is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:20 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.