BF173 transistor question - UK Vintage Radio Repair and Restoration Discussion Forum

greg_simons · 1st Jun 2019, 10:23 pm

As many here will know I'm restoring a thorn 2k, long job!, well I've got to the if strip and have to replace several bf173's that have rotted off the board, new ones have been obtained but,,,when inserted into my cheapo transistor tester it shows a diode strapped twist collector and emitter, a check with the meter shows the same, I thought they were just a bipolar device, can anyone explain and have I got the right devices, this should be something I know but don't I think!.
Greg.

vidjoman · 1st Jun 2019, 10:43 pm

Data sheet shows an NPN transistor with 4 legs - clockwise from the tab - base, emitter, collector, case.

ctc15 · 2nd Jun 2019, 7:59 pm

Hi Greg
The diode strapped between collector and emitter is the integrated screen to minimise the undesirable collector - base capacitance.
Keith

greg_simons · 2nd Jun 2019, 8:17 pm

Hi Keith
Many thanks for that info, it makes sense now, if it hadn't been for that cheap tester I wouldn't be asking the question, the project continues,,,,

greg_simons · 3rd Jun 2019, 8:19 am

Ok mods, looks like I have the answer to my question, I'd forgotten miller capacitance, this thread can be closed.
Greg.

1st Jun 2019, 10:23 pm	#1
greg_simons Octode Join Date: Jul 2004 Location: Evesham, Worcestershire, UK. Posts: 1,423	BF173 transistor question As many here will know I'm restoring a thorn 2k, long job!, well I've got to the if strip and have to replace several bf173's that have rotted off the board, new ones have been obtained but,,,when inserted into my cheapo transistor tester it shows a diode strapped twist collector and emitter, a check with the meter shows the same, I thought they were just a bipolar device, can anyone explain and have I got the right devices, this should be something I know but don't I think!. Greg. __________________ Picture, sound?, DOOR.

1st Jun 2019, 10:43 pm	#2
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: bf173 transistor question Data sheet shows an NPN transistor with 4 legs - clockwise from the tab - base, emitter, collector, case.

2nd Jun 2019, 7:59 pm	#3
ctc15 Pentode Join Date: Oct 2005 Location: Barnet, London, UK. Posts: 167	Re: BF173 transistor question Hi Greg The diode strapped between collector and emitter is the integrated screen to minimise the undesirable collector - base capacitance. Keith

2nd Jun 2019, 8:17 pm	#4
greg_simons Octode Join Date: Jul 2004 Location: Evesham, Worcestershire, UK. Posts: 1,423	Re: BF173 transistor question Hi Keith Many thanks for that info, it makes sense now, if it hadn't been for that cheap tester I wouldn't be asking the question, the project continues,,,, __________________ Picture, sound?, DOOR.

3rd Jun 2019, 8:19 am	#5
greg_simons Octode Join Date: Jul 2004 Location: Evesham, Worcestershire, UK. Posts: 1,423	Re: BF173 transistor question Ok mods, looks like I have the answer to my question, I'd forgotten miller capacitance, this thread can be closed. Greg. __________________ Picture, sound?, DOOR.