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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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5th Sep 2018, 2:52 pm | #1 |
Tetrode
Join Date: Nov 2011
Location: London, UK.
Posts: 90
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Bearcat BC-220 FB
Hi all,
I was given a dead Bearcat BC-220 FB scanner several years ago, which I've just got around to checking. It looks like the transformer's primary winding is open circuit, hence showing no signs of life when powered on. It can be powered from an external 13.8V DC supply but for convenience I intend to repair the internal mains supply, if possible. According to the service manual, the power specifications for the scanner are "117Vac 20W, 13.8Vdc 9W". Translating that to a 230VAC mains supply (UK) I presume the transformer wattage would be unchanged at 20W. My question is if I replace the internal transformer would a transformer with the following specifications suffice: 230VAC 20VA 8v-0-8V with tappings? The service manual states the output from the original transformer is 16VAC; however, there are three tappings soldered to the PCB, which I presume are 8V-0-8V. Service manual: http://www.repeater-builder.com/unid...20-svc-man.pdf Thanks Ade Last edited by 3Phase615V; 5th Sep 2018 at 3:03 pm. |
5th Sep 2018, 5:32 pm | #2 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
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Re: Bearcat BC-220 FB
I hope somebody hasn't connected it to 240V instead of 115V and burnt out the transformer. That may have overloaded the radio circuit. Might be best to give it a check on 12V just in case the radio has been damaged before changing the transformer. You will need to half the value of the original mains input fuse if powering it from 240V instead of 115V. Check polarity of the 12V input socket as sometimes these were reversed. i.e centre pin negative not positive. I like Bearcat scanners. They seem to be well designed and perform well.
Alan. |
5th Sep 2018, 6:00 pm | #3 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,935
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Re: Bearcat BC-220 FB
It has been checked out 13.8V DC and appears ok.
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5th Sep 2018, 6:04 pm | #4 |
Tetrode
Join Date: Dec 2012
Location: Andover, Hampshire, UK.
Posts: 85
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Re: Bearcat BC-220 FB
I have one of these which was supplied fitted with a 240V transformer for the UK. Output is centre tapped. There is a mod that allows switching between AM and FM.
John |
5th Sep 2018, 7:33 pm | #5 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
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Re: Bearcat BC-220 FB
Whoops, mis-interpreted the remark on DC power.
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5th Sep 2018, 9:02 pm | #6 |
Tetrode
Join Date: Nov 2011
Location: London, UK.
Posts: 90
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Re: Bearcat BC-220 FB
Yes, sorry, perhaps I should have made it clearer that the radio is the 240VAC version, according to the two-pin power socket label. The radio appears to power on okay through the DC input at 13.8V but I've had to disassemble, clean, lubricate and reassemble the on/off volume and auto/squelch pots as they were both functioning poorly. The DC input is just a red lead to a positive spade connector input and a black lead to a solder tag on the case.
So regarding a replacement transformer, a 230VAC 20VA 8V-0-8V with tappings would be suitable? That's interesting regarding the AM/FM mod. I'll take a look into that one once I've got the transformer sorted. |
7th Sep 2018, 2:38 pm | #7 |
Heptode
Join Date: Nov 2009
Location: London, Ontario, Canada
Posts: 675
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Re: Bearcat BC-220 FB
Hi Ade,
A 8V - 0V - 8V transformer would give you only about 10.5VDC unloaded. For 13.8VDC you would need something more like a 10V - 0V - 10V transformer. Regards, Peter Last edited by orbanp1; 7th Sep 2018 at 2:45 pm. |
8th Sep 2018, 3:39 am | #8 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,343
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Re: Bearcat BC-220 FB
The mains transformer generates 16v DC unloaded according to the description in the manual, 8-0-8 or even 10-0-10 is not going to cut it.
You would be looking closer to 12-0-12. This 16v is is not used to run anything directly in the rig, it is regulated to 5, 9 and 11v internally. |
9th Sep 2018, 12:46 am | #9 |
Tetrode
Join Date: Nov 2011
Location: London, UK.
Posts: 90
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Re: Bearcat BC-220 FB
Thanks Peter and Terry. I can see that I mistakenly quoted the service manual stating 16VAC output from the transformer, which of course caused an underestimation of the transformer output.
I think I will go with a 12V-0-12V transformer as you've suggested, Terry, as, as a friend advised, some margin for ripple voltage would be wise. |
9th Sep 2018, 2:14 am | #10 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,343
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Re: Bearcat BC-220 FB
Good luck, let us know how you get on with the repair.
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10th Sep 2018, 1:29 am | #11 |
Tetrode
Join Date: Nov 2011
Location: London, UK.
Posts: 90
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Re: Bearcat BC-220 FB
Yes,will do. Thanks Terry and all.
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