Blaupunkt Pop 70 radio transistor query - UK Vintage Radio Repair and Restoration Discussion Forum

Nukeybrown · 24th Jun 2017, 3:24 pm

The above set seems to have an issue at bottom end of bass , hard to describe but its like it distorts right at the bottom. Have used diff speakers and still the same. I know sound issues are hard to pin down but ive checked majority of the bass circuit except for the transistor. On the schematics the transistor is showing as bc108c but in the set it has a bc172c. I have got bc108c in my box of many things but the bc108c is tin pot transistor and the one that is in is silicon black. Looks original but not 100% sure. So my question is are they the same? Or comparable, which one is preferable? Could this be my bass issue. Thanks for any help. There are a lot of tin pot transistors on the board but only 2 of the bc172c , the one in the picture and also one slightly further up the top of the picture.

AC/HL · 24th Jun 2017, 8:27 pm

They're both NPN general purpose transistors, both the same gain band, so there's nothing really to choose between them. A look at the print side should prove whether they're originals or replacements.

Biggles · 24th Jun 2017, 11:06 pm

Regarding the fault, it may be worth feeding some audio from another source into the audio amp around the volume pot just to check whether it is actually the amp causing the distortion. I have had faults that cause distortion from tuning issues or in the detector stage.
Alan.

Andrew2 · 24th Jun 2017, 11:25 pm

Likewise, Alan. The electrolytics on the AGC line often go low in value and cause distortion on heavy bass. I've had this problem on quite a few early transistor models.

paulsherwin · 25th Jun 2017, 11:30 am

It is very unlikely that a transistor fault would cause these symptoms.

The electrolytics on the right of the photo look a bit unhappy, but it may be caused by the lighting.

Nukeybrown · 25th Jun 2017, 10:04 pm

Yeah thats just lighting paul, they have plastic sleeves around them

24th Jun 2017, 3:24 pm	#1
Nukeybrown Heptode Join Date: Jan 2016 Location: Gateshead, Tyne and Wear, UK. Posts: 504	Blaupunkt Pop 70 radio transistor query The above set seems to have an issue at bottom end of bass , hard to describe but its like it distorts right at the bottom. Have used diff speakers and still the same. I know sound issues are hard to pin down but ive checked majority of the bass circuit except for the transistor. On the schematics the transistor is showing as bc108c but in the set it has a bc172c. I have got bc108c in my box of many things but the bc108c is tin pot transistor and the one that is in is silicon black. Looks original but not 100% sure. So my question is are they the same? Or comparable, which one is preferable? Could this be my bass issue. Thanks for any help. There are a lot of tin pot transistors on the board but only 2 of the bc172c , the one in the picture and also one slightly further up the top of the picture. Attached Thumbnails

24th Jun 2017, 8:27 pm	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Blaupunkt Pop 70 radio transistor query They're both NPN general purpose transistors, both the same gain band, so there's nothing really to choose between them. A look at the print side should prove whether they're originals or replacements.

24th Jun 2017, 11:06 pm	#3
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Blaupunkt Pop 70 radio transistor query Regarding the fault, it may be worth feeding some audio from another source into the audio amp around the volume pot just to check whether it is actually the amp causing the distortion. I have had faults that cause distortion from tuning issues or in the detector stage. Alan.

24th Jun 2017, 11:25 pm	#4
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,038	Re: Blaupunkt Pop 70 radio transistor query Likewise, Alan. The electrolytics on the AGC line often go low in value and cause distortion on heavy bass. I've had this problem on quite a few early transistor models. __________________ Andy G1HBE.

25th Jun 2017, 11:30 am	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,966	Re: Blaupunkt Pop 70 radio transistor query It is very unlikely that a transistor fault would cause these symptoms. The electrolytics on the right of the photo look a bit unhappy, but it may be caused by the lighting.

25th Jun 2017, 10:04 pm	#6
Nukeybrown Heptode Join Date: Jan 2016 Location: Gateshead, Tyne and Wear, UK. Posts: 504	Re: Blaupunkt Pop 70 radio transistor query Yeah thats just lighting paul, they have plastic sleeves around them