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1966 Cessna 150F Radio Voltage Problem/Question

2011-03-23 22:09:10

1966 Cessna 150F Radio Voltage Problem/Question

Here it goes... This is driving me crazy, and I have looked almost everywhere for an answer. Even the local radio shop does not know...

I have a 1966 Cessna 150F that has a RT385 marked 28 volts on the rear, and it has been working in this aircraft since before I purchased it. It finally has decided to "take a dump" and the plan is to replace it with a TKM. So far, so good... The aircraft has 1 each 14 volt battery, and the voltage readout on the rack connector is showing 26 volts with the engine not running. Did Cessna install a voltage doubler so that 28 volt radios would work? I have several maintenance manuals, but for the life of me everything I find shows that this aircraft is 14 volts. Hope I did the right thing, but ordered a RT385 replacement from TKM smile

Thanks in advance,
Jack "Puzzled" Sharp

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2011-03-25 08:13:15

Re: 1966 Cessna 150F Radio Voltage Problem/Question

Get a multi-meter, find the power cable going into the radio, in most cases it would be red, or red with a stripe, measure from that to ground. If the reading truly is in the 24 - 28 volt range, there is a conveter in the system somewhere. By-pass this for radio power if installing a 12 V radio, just take power from anywhere in the buss that reads 12 V. The other option is that the voltmeter in your A/C has been re-wired to read double voltage. In that case, just plug it in and remember the double reading when interpreting the meter in-flight.

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2011-03-25 16:34:06

Re: 1966 Cessna 150F Radio Voltage Problem/Question

Thanks for the reply. I know there is 28 volts on the radio buss because I had already measured it.Was it normal for Cessna to install a converter on that year, and if so where do they mount it. We can not find one. I may have to start at the radio tray and start tracing backwards smile