FT101E -100 volts bias ?

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FT101E -100 volts bias ?

Postby VE2PBC » Tue May 14, 2019 9:25 pm

Hello, I have a Yaesu ft101e and I always wondered why Yaesu indicte on its rectifier Board (PB-1076b) an output at -100 volt DC. In reality it produces a voltage of more than -160 volts DC. 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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Re: FT101E -100 volts bias ?

Postby w6nfu » Sun May 19, 2019 2:23 am

Sure looks normal. Both voltages, -100 and +160 are derived from the 120-V secondary winding of the power transformer.
-100 goes to a regulator MJ(6) and out on Pin 2 for Bias to V2 and V3, the 6JS6C power output tubes plus to Pin 3 on the Accessory Plug.
+160 goes to the Grids of V2 and V3 (Pins 3 and 11) plus to Pin 6 of the Accessory Plug, perhaps to power the external VFO or ?

Is this what you have?

I'm no expert on the FT-101's, but do have all the Fox Tango Club annual books and notes by Milt Lowen, used when I had a trusty FT-101 back in 1971 thru 1975. If interested in a special FT-101 Series alignment and service information that is displayed pictorially on four pages that can be taped together and back to back, I'd be glad to email them to you. It saves wading thru pages of the manual and was a good resource way back when. The FT-101 is a great radio.
Dave - w6nfu
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Re: FT101E -100 volts bias ?

Postby VE2PBC » Mon May 20, 2019 2:11 am

Thanks Dave for taking the time to answer me, my reading with my DMM at the -100 Vdc output of the rectifier board is -169 Vdc exactly the same value as my output 160 Vdc rectifier board (169 Vdc). An amateur radio on another forum told me that was a mistake from Yaesu, He should have entered -160 Vdc on the board and in the schematic of the service manual instead of -100 Vdc. It was explained to me that the two outputs -100 Vdc and 160 Vdc come from the same secondary winding of the power transformer. I am interested in the information published by Fox tango it would be appreciated to send me by email. lpbourdeau@videotron.ca. Thanks again. Louis Philippe 73 VE2PBC
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Re: FT101E -100 volts bias ?

Postby w6nfu » Mon May 20, 2019 3:32 pm

Louis,

Very interesting measurements on your FT-101. Are you able to adjust the BIAS normally?
I just sent you an email with the four pages of FT-101 Alignment info attached, designed by Frank W. Sechrist W6AIY and edited by Milton Lowens WA2AOQ, publisher of the Fox Tango Club Newsletters back in June 1975. I believe both are now deceased.

Hope this helps,
Dave - w6nfu
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