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PA tubes changed from 6JS6C sweep tubes to 6146B following the QST article of May 1999 and
addendum (Hints & Kinks) September 1999. Original QST article by Roger Davis ZS1J.
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Yaesu FT-101EE |
Original Sweep tube sockets |
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Ceramic octal sockets The QST article was followed with some exceptions. 6146B tubes were not used, 6883B tubes were used instead. The 6883B is the equivalent of a 6146B with a 12 Volt filament. Each cathode pin was bypassed with a .002 2KV disc capacitor. Each screen grid was bypassed with a .01 3KV disc capacitor. C-16 to the RCA jack was removed to make room for bypass capacitors at the socket. Filaments rewired for 12 volts, each filament bypassed with a .01 3KV disc capacitor. None of the Yaesu capacitors removed from the PA sockets were reused. |
| 400 pf disc capacitor (Red circle) added to neut feedback in order to allow variable neut capacitor to be midrange when PA is neutralized. |
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20 pf Variable trimmer added across coil T-103 required to tune 10 meter band. |
| Schematic with new modifications indicated. 400 pf (Red) required in this transmitter to allow variable neutralizing capacitor (TC-27) to be within range. September 1999 QST addendum suggested 2000 pf. 20 pf variable trimmer (blue) added across T-103 to permit 10 meter tuning. C16 (Green) to RF out RCA jack removed since I do not use it and it provided additional room for ceramic octal sockets and bypass capacitors. |
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New PA Schematic. |
Neutralizing. |
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Remove screen grid voltage from PA, unsolder orange wire at feedthru capacitor. Replace sheet metal shields. Turn on AC and Filaments, terminate the antenna jack in 50 ohms, connect oscilloscope across 50 ohm load on antenna. With the transmitter on 10 or 15 meter band, key the rig (MOX in TUNE mode), advance the carrier control 1/3 to 1/2 rotation, peak preselect, Plate and Loading for maximum indication on the scope, minimize the scope display with the Neutralizing capacitor TC27. Re-peak the Plate and Loading for maximum indication, minimize display with Neut capacitor, repeat the process until Plate and Loading have no increase on the display when the neut cap has the display minimized. Shutdown the transmitter, discharge high voltage power supply voltages. Resolder Plate and Screen wires. If Neutralizing capacitor TC27 reaches full mesh or wide open, adjust the value of shunt capacitor across C11. 400 Pf worked on this transmitter, 2000 pf was the suggested value from the Sept 1999 QST article. |
| Other Changes Required. Following the completion of the modification, PA idle current was unable to be adjusted below 80 ma. The article suggests 60 ma idle current. On circuit board PB-1547, Reg & Calib unit, resistor R4 changed to 4.7k (Red), resistor R2 changed to 15k (Blue). The PA idle current can be adjusted from cutoff to 100+ma idle current. |
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