Armstrong 600 series tuners and receivers - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

PaulR · 19th Dec 2020, 7:16 pm

I set mine to 20mA and all seems well. One unit still has the original 2N3055 output transistors but I replaced them on the other one with 2N3773s as a couple had blown and both are fine with 20mA.

I thought that the 0.47 resistors on mine had drifted which was another reason I replaced them but I think they were probably ok and my multimeter wasn't able to measure such a low resistance accurately.

stevehertz · 20th Dec 2020, 6:51 pm

Quiescent current now set. Before doing so I applied contact cleaner to the pots and gave them a good end to ending. Then I applied Electrolube and did the same again, nice and smooth and full contact end to end. QC set at a stable 20mA on both channels.

Regarding the lack of AM, I took the output from the AM board and fed it to my Bose Soundlink Mini powered speaker. Tellingly I could tune in to quite a few stations. Not so sure if the level was correct, but I was certainly able to get enough boost from the Bose to listen to the stations, something that is not possible in the receiver itself. So, it would appear that the AM board is working 'at least ok', but for some reason the signal it is not getting through to the preamp and power amp. Investigations continue.

Trevor · 20th Dec 2020, 7:58 pm

If you look into an earlier post I did say the you could have used the amp to test itself i.e. take a signal from the Am board to the amp maybe to the vol control if you have your scope it should be a simple matter to trac the signal through any way well done you are making progress
regatds Trev

stevehertz · 20th Dec 2020, 8:21 pm

Can someone provide a clear close up photo of the wiring on the top side of the 'AM' switch please? I'm not sure if mine has been got at in the past. I'd like to check the colours of the wires, which terminals they go to and how many on each post. Thanks.

I've also noticed that on shots of the above on the internet, although they're not close up like I need, some 626 sets have an electrolytic cap across a couple of the terminals.

stevehertz · 28th Dec 2020, 1:17 pm

I'm making very slow (no?) progress in trying to find out why I'm not able to get AM on this set. I have taken separate signals from the diode switching board as they come in from both the FM tuner and the AM tuner boards. When feeding these into my Bose Soundlink Mini powered speaker, the FM signal is much louder than the AM one. I can tune in to stations in AM and listen to them on the Bose. This suggests to me that the signal level coming from the AM board is very low for some reason. The AM tuner is 'working' but the signal level is low. I'm down to measuring component values on the AM board, and I have tested the six transistors out of circuit and they all test ok.

PaulR · 28th Dec 2020, 2:21 pm

Fishing in the dark here but is the power supply to the AM board ok? I have had problems with bad interconnect solder joints on these. Neither of mine have AM unfortunately.

stevehertz · 28th Dec 2020, 3:19 pm

Quote:

Originally Posted by PaulR

Fishing in the dark here but is the power supply to the AM board ok? I have had problems with bad interconnect solder joints on these. Neither of mine have AM unfortunately.

Hi Paul, some time ago I did a voltage check of that nature, but probably best if double check.

PaulR · 28th Dec 2020, 4:49 pm

I am very far from being an expert but the thought occurred to me as a similar problem has just arisen on an item of my son's.

stevehertz · 2nd Jan 2021, 5:01 pm

I've found a fault on the AM board and I thought it would cure the lack of AM. It didn't. There's a 0.1uf disc ceramic cap on the output of the AM board and it was considerably leaky. Changing it made no difference, still no AM.

There's quite a few caps on the diode switching board that are depicted on the schematic as 'normal' caps ie not electrolytic types, yet electrolytics are fitted. Other caps are depicted as electrolytic types and are fitted as such. Confusing. Looking at photos of other sets on the internet, they too have electrolytics fitted where the schematic shows normal, non-electrolytic caps. Any thoughts on this?

PaulR · 2nd Jan 2021, 6:34 pm

I have often wondered why electrolytics were sometimes used when the same value of non-electrolytic are available. Maybe larger value non-electrolytics became more available during the production run.

Radio Wrangler · 2nd Jan 2021, 6:59 pm

Maybe someone is using the ESR of an electrolytic to cure an instability. It's not an obvious or well known bodge, but it happens.

David

stevehertz · 4th Jan 2021, 6:35 pm

At last, I've found the fault. Looking at voltages around the preamp and diode switching board, there were many that were way too high and just didn't add up, for example the voltages at both ends of a resistor being virtually the same. Similarly, the voltages on all three pins of transistors not only being very similar, but high at around 30V. No voltage drop means no current is flowing, so something is open circuit. Eventually I checked the 'voltage' from the end of a resistor that was (supposed to be) connected to chassis. It too read 30V, not zero! Clearly the chassis connection was adrift somehow. Checking around I eventually noticed that a short section of PCB track was missing. I hadn't spotted it previously because the 'ghost' of the track was a very similar shade of green to the other tracks that were covered in a green lacquer. Re-instating the link with a length of single strand copper wire brought in AM loud and clear. Actually, there was another short link of 'earth' track missing from the DIN tape socket that I also replaced. The problematic missing piece of track can be seen in the top right hand corner of the two photos here.

I am still looking for a centre tuning meter for this set, if anyone can help please see my separate wanted ad: https://www.vintage-radio.net/forum/...d.php?t=173805

PaulR · 4th Jan 2021, 7:28 pm

Well done, Steve. Presumably the track was there at some point in the past?

stevehertz · 4th Jan 2021, 7:36 pm

Quote:

Originally Posted by PaulR

Well done, Steve. Presumably the track was there at some point in the past?

Well yes it must have been. There's evidence of a burn on the aluminium chassis below that area so somehow someone has caused a short resulting in those two lengths of track vaporising.

Trevor · 4th Jan 2021, 8:37 pm

Nice one well done So pleased that you have sorted it
these things come with a lot of history and wear the scars of their past Some times all it needs is hard work
Trev

stevehertz · 4th Jan 2021, 9:34 pm

I bought the receiver described as working in need of some TLC. Quite an understatement as it turns out. I haven't mentioned lots of other faults and problems. But anyway, I'm getting there and this AM fault was proving to be a major hurdle. Ironically I had previously checked that the PCB's chassis terminal was connected to chassis - it was - but you don't think that the track going from that terminal has been atomised!

Trevor · 5th Jan 2021, 10:07 am

it seems to me a device with a live earth fault was connected at the tape din socket this then blew oc the earth connection via the din socket etc I used to be in the hfi trade and came acros this on a few occasions
Trev

PaulR · 5th Jan 2021, 10:17 am

What about doing a "success story" about all the work you have done on it? It would make interesting and informative reading.

stevehertz · 5th Jan 2021, 11:07 am

Nice thought Paul, but in truth, most of the 'talk' on this thread is about me bumbling around trying to find a fault. There's lots of threads on here about restoration work on the 600 series as I found out when doing a search for the same. Not really got time at the moment. For one, this set still needs a lot of work and of course the mountain of other non-wireless stuff that I have to do. Plus a dozen or so sets to work on. You know how it is. Thanks to all who have provided help.

Radio Wrangler · 5th Jan 2021, 11:58 am

It is one of the gross unfairnesses of our universe, that an awkward fault which seems so intractable at the time and which takes serious perseverance to track down, suddenly becomes another 'oh, that' once it's been understood.

This thread is the saga of some good work, and the perseverance needed to keep on going and not lose track of reality when things seem to have stopped stacking up. It comes to a successful conclusion and Steve has a cute little amp to show for it.

Engineering is mostly about problem solving. Once solved, problems always seem smaller than they really were. Consequently, at the annual review, it is hard to impress bosses that you did something significant :-(

David

19th Dec 2020, 7:16 pm	#61
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,237	Re: Armstrong 600 series tuners and receivers I set mine to 20mA and all seems well. One unit still has the original 2N3055 output transistors but I replaced them on the other one with 2N3773s as a couple had blown and both are fine with 20mA. I thought that the 0.47 resistors on mine had drifted which was another reason I replaced them but I think they were probably ok and my multimeter wasn't able to measure such a low resistance accurately. __________________ Paul

20th Dec 2020, 6:51 pm	#62
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers Quiescent current now set. Before doing so I applied contact cleaner to the pots and gave them a good end to ending. Then I applied Electrolube and did the same again, nice and smooth and full contact end to end. QC set at a stable 20mA on both channels. Regarding the lack of AM, I took the output from the AM board and fed it to my Bose Soundlink Mini powered speaker. Tellingly I could tune in to quite a few stations. Not so sure if the level was correct, but I was certainly able to get enough boost from the Bose to listen to the stations, something that is not possible in the receiver itself. So, it would appear that the AM board is working 'at least ok', but for some reason the signal it is not getting through to the preamp and power amp. Investigations continue. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

20th Dec 2020, 7:58 pm	#63
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: Armstrong 600 series tuners and receivers If you look into an earlier post I did say the you could have used the amp to test itself i.e. take a signal from the Am board to the amp maybe to the vol control if you have your scope it should be a simple matter to trac the signal through any way well done you are making progress regatds Trev

20th Dec 2020, 8:21 pm	#64
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers Can someone provide a clear close up photo of the wiring on the top side of the 'AM' switch please? I'm not sure if mine has been got at in the past. I'd like to check the colours of the wires, which terminals they go to and how many on each post. Thanks. I've also noticed that on shots of the above on the internet, although they're not close up like I need, some 626 sets have an electrolytic cap across a couple of the terminals. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

28th Dec 2020, 1:17 pm	#65
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers I'm making very slow (no?) progress in trying to find out why I'm not able to get AM on this set. I have taken separate signals from the diode switching board as they come in from both the FM tuner and the AM tuner boards. When feeding these into my Bose Soundlink Mini powered speaker, the FM signal is much louder than the AM one. I can tune in to stations in AM and listen to them on the Bose. This suggests to me that the signal level coming from the AM board is very low for some reason. The AM tuner is 'working' but the signal level is low. I'm down to measuring component values on the AM board, and I have tested the six transistors out of circuit and they all test ok. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

28th Dec 2020, 2:21 pm	#66
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,237	Re: Armstrong 600 series tuners and receivers Fishing in the dark here but is the power supply to the AM board ok? I have had problems with bad interconnect solder joints on these. Neither of mine have AM unfortunately. __________________ Paul

28th Dec 2020, 4:49 pm	#68
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,237	Re: Armstrong 600 series tuners and receivers I am very far from being an expert but the thought occurred to me as a similar problem has just arisen on an item of my son's. __________________ Paul

2nd Jan 2021, 5:01 pm	#69
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers I've found a fault on the AM board and I thought it would cure the lack of AM. It didn't. There's a 0.1uf disc ceramic cap on the output of the AM board and it was considerably leaky. Changing it made no difference, still no AM. There's quite a few caps on the diode switching board that are depicted on the schematic as 'normal' caps ie not electrolytic types, yet electrolytics are fitted. Other caps are depicted as electrolytic types and are fitted as such. Confusing. Looking at photos of other sets on the internet, they too have electrolytics fitted where the schematic shows normal, non-electrolytic caps. Any thoughts on this? __________________ A digital radio is the latest thing, but a vintage wireless is forever..

2nd Jan 2021, 6:34 pm	#70
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,237	Re: Armstrong 600 series tuners and receivers I have often wondered why electrolytics were sometimes used when the same value of non-electrolytic are available. Maybe larger value non-electrolytics became more available during the production run. __________________ Paul

2nd Jan 2021, 6:59 pm	#71
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,903	Re: Armstrong 600 series tuners and receivers Maybe someone is using the ESR of an electrolytic to cure an instability. It's not an obvious or well known bodge, but it happens. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

4th Jan 2021, 6:35 pm	#72
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers At last, I've found the fault. Looking at voltages around the preamp and diode switching board, there were many that were way too high and just didn't add up, for example the voltages at both ends of a resistor being virtually the same. Similarly, the voltages on all three pins of transistors not only being very similar, but high at around 30V. No voltage drop means no current is flowing, so something is open circuit. Eventually I checked the 'voltage' from the end of a resistor that was (supposed to be) connected to chassis. It too read 30V, not zero! Clearly the chassis connection was adrift somehow. Checking around I eventually noticed that a short section of PCB track was missing. I hadn't spotted it previously because the 'ghost' of the track was a very similar shade of green to the other tracks that were covered in a green lacquer. Re-instating the link with a length of single strand copper wire brought in AM loud and clear. Actually, there was another short link of 'earth' track missing from the DIN tape socket that I also replaced. The problematic missing piece of track can be seen in the top right hand corner of the two photos here. I am still looking for a centre tuning meter for this set, if anyone can help please see my separate wanted ad: https://www.vintage-radio.net/forum/...d.php?t=173805 Attached Thumbnails __________________ A digital radio is the latest thing, but a vintage wireless is forever..

4th Jan 2021, 7:28 pm	#73
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,237	Re: Armstrong 600 series tuners and receivers Well done, Steve. Presumably the track was there at some point in the past? __________________ Paul

4th Jan 2021, 8:37 pm	#75
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: Armstrong 600 series tuners and receivers Nice one well done So pleased that you have sorted it these things come with a lot of history and wear the scars of their past Some times all it needs is hard work Trev

4th Jan 2021, 9:34 pm	#76
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers I bought the receiver described as working in need of some TLC. Quite an understatement as it turns out. I haven't mentioned lots of other faults and problems. But anyway, I'm getting there and this AM fault was proving to be a major hurdle. Ironically I had previously checked that the PCB's chassis terminal was connected to chassis - it was - but you don't think that the track going from that terminal has been atomised! __________________ A digital radio is the latest thing, but a vintage wireless is forever..

5th Jan 2021, 10:07 am	#77
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: Armstrong 600 series tuners and receivers it seems to me a device with a live earth fault was connected at the tape din socket this then blew oc the earth connection via the din socket etc I used to be in the hfi trade and came acros this on a few occasions Trev

5th Jan 2021, 10:17 am	#78
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,237	Re: Armstrong 600 series tuners and receivers What about doing a "success story" about all the work you have done on it? It would make interesting and informative reading. __________________ Paul

5th Jan 2021, 11:07 am	#79
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Armstrong 600 series tuners and receivers Nice thought Paul, but in truth, most of the 'talk' on this thread is about me bumbling around trying to find a fault. There's lots of threads on here about restoration work on the 600 series as I found out when doing a search for the same. Not really got time at the moment. For one, this set still needs a lot of work and of course the mountain of other non-wireless stuff that I have to do. Plus a dozen or so sets to work on. You know how it is. Thanks to all who have provided help. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

5th Jan 2021, 11:58 am	#80
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,903	Re: Armstrong 600 series tuners and receivers It is one of the gross unfairnesses of our universe, that an awkward fault which seems so intractable at the time and which takes serious perseverance to track down, suddenly becomes another 'oh, that' once it's been understood. This thread is the saga of some good work, and the perseverance needed to keep on going and not lose track of reality when things seem to have stopped stacking up. It comes to a successful conclusion and Steve has a cute little amp to show for it. Engineering is mostly about problem solving. Once solved, problems always seem smaller than they really were. Consequently, at the annual review, it is hard to impress bosses that you did something significant :-( David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done