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Author Topic: FT101E -100 volts DC bias ?  (Read 973 times)
VE2PBC
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« on: May 15, 2019, 01:07:50 PM »

Hello, I have a Yaesu ft101e and I always wondered why Yaesu indicte on its panel rectifier (PB-1076b) an output at -100 volt DC. In reality it produces a voltage of more than -160 volts. In the schematic of the service manual, the output -100 volts DC and 160 volt DC are produced by the same voltage doubler. is this normal? Louis Philippe. 73 VE2PBC
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HAMHOCK75
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« Reply #1 on: May 15, 2019, 07:21:25 PM »

It's a mistake on both the board and in the manual. If you look at the schematic the -100 VDC and the +160 VDC are half wave rectifiers off the same 120 VAC transformer winding. The only difference is the diodes are opposite in direction. So the correct labels should be +/- 160 VDC not +160 VDC and -100 VDC.
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VE2PBC
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« Reply #2 on: May 15, 2019, 08:07:31 PM »

Thank you Hamhock75, happy with this answer, I thought that the two capacitors C4 and C2 that do not have the same value of micro farad could influence the negative voltage. thank you again Louis-Philippe 73
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HAMHOCK75
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« Reply #3 on: May 16, 2019, 01:03:15 AM »

Quote from: VE2PBC
thought that the two capacitors C4 and C2 that do not have the same value of micro farad could influence the negative voltage

I think you meant to say C7, C8 in parallel ( both 22 ufd, 250 WVDC ) filtering the +160 VDC versus C2, C1, and R8 ( C2 = 22 ufd, 250 WVDC, C1 = 22 ufd, 160 WVDC, and R8 = 6.8K ) filtering the -160 VDC.

C4 is part of the regulated +6 VDC for the VFO.

Just noticed that this is only your second post. Welcome to eham.net!
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VE2PBC
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« Reply #4 on: May 16, 2019, 01:18:46 PM »

Hello, I was referring to the rectifying board. The two capacitors of the circuit +/- 160 volts DC, C2 (.0047 uf / 1.4 Kvolt) and C4 (.01 uf / 500 volts) not going the same value in uf I thought that could explain the error of -100 volts. indicated on the board. I appreciate that you take the time to give me information, there are not many people who have experience on these old platforms. Thank you. Louis-Philippe 73
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HAMHOCK75
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« Reply #5 on: May 16, 2019, 02:20:46 PM »

I see now what you meant. Those capacitors are not intended to filter the 60 Hz related frequencies so they have little effect on the DC voltage. They serve mostly to keep higher frequencies created by the FT101 from going back out and onto the AC line. C2 is across the transformer secondary so it affects high frequencies on both the +/-160 VDC's. C4 is only across the +160 VDC output.
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VE2PBC
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« Reply #6 on: May 17, 2019, 01:06:19 PM »

I now understand the use of these capacitors. One last question then how did the Yaesu engineers calculate to get the outputs at +/- 160 VOLTS DC from 120 volts AC?
(Volt ac X Volt rms = Volt dc) ?
Louis-Philippe 73
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HAMHOCK75
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« Reply #7 on: May 17, 2019, 01:39:20 PM »

Good question. Like this.



The transformer output is 120 VAC ( rms ). Which is +/- 170 Vpeak. The rectifiers conduct up to the peak voltage which is then stored on the capacitors reduced by losses due to the diode junction voltage, resistance in transformer windings, current drain from loads etc.
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VE2PBC
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« Reply #8 on: May 18, 2019, 07:07:25 PM »

Super as an explanation, if I understand your information, my DMM gives me a reading AC value RMS and DC reading AVG value. The load connected to the output of the rectifier (ex: 160 volts) determines its voltage that I measure with my DMM. If this is O.K I just update my knowledge with your help. Louis-Philippe 73. Thank you
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HAMHOCK75
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« Reply #9 on: May 19, 2019, 11:30:38 AM »

Yes, that is correct. For large signals, this is the model for the diode where the output voltage is proportional to the input voltage. For small signals, it changes, the output voltage becomes proportional to the square of the input voltage which allows diodes to be used as power detectors and mixers.
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