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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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18th Jan 2022, 7:28 am | #1 |
Diode
Join Date: Dec 2021
Location: Preston, Lancashire, UK.
Posts: 6
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Hacker RP78 Working Current?
Hi folks, I managed to find a replacement BC465 for the RP78 as the original one was split. Fitted it, and checked the cap across the battery input. It works well enough on all bands, but is drawing around 80mA on FM at moderate volume. This seems high, any suggestions on anything else I can check etc? Thanks, Russ.
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20th Jan 2022, 1:08 pm | #2 |
Hexode
Join Date: Aug 2007
Location: S.W. London, UK.
Posts: 416
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Re: Hacker RP78 Working Current?
Hi Russ, I have a RP78 and have taken some measurements for you. The figures are for total current from the battery terminals at 9 volts.
FM mode tuned to a station; 23mA, Volume at minimum 25mA, Volume at my normal listening level 40mA+, Volume at moderately loud --------- AM mode tuned to a station; 19.5mA, Volume at minimum 21.5mA, Volume at my normal listening level 40mA+, Volume at moderately loud Your value of 80mA does seem excessive. As you have been working in the output stage it would be wise to check the output stage quiescent current setting. Vic |
21st Jan 2022, 3:56 pm | #3 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,668
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Re: Hacker RP78 Working Current?
__________________
-- Graham. G3ZVT |
23rd Jan 2022, 4:39 pm | #4 |
Diode
Join Date: Dec 2021
Location: Preston, Lancashire, UK.
Posts: 6
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Re: Hacker RP78 Working Current?
Thanks Vic, much appreciated. I'll have a look at it tomorrow. Apologies for the ignorance, but that will the pot on the output stage board? Cheers, Russ.
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23rd Jan 2022, 7:11 pm | #5 |
Diode
Join Date: Dec 2021
Location: Preston, Lancashire, UK.
Posts: 6
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Re: Hacker RP78 Working Current?
Tremendous progress! I tried adjusting the current with the pot, and it made no difference at all. So, I removed it from the board and checked the resistance, and it is fine. I took both electrolytics out of the board, tested them and the 1000uf was short circuit. Replaced with a decent used one (slightly smaller) and I've set the rest current to 23ma. It's singing away now! Happy days!
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