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G4WYZ MikeyP · 25th Feb 2018, 12:45 pm

Phase Detector -again!

The original fault on the Phase Detector was no varactor voltage, Q16 U898E was replaced with a 2N3819 resulted in the correct voltage tuning range of 3.6 – 14.8 volts.

Then the flaky PSU folded again it had folded a number of times, although the 2N3055 always worked when tested, it was replaced with a new one and all the issued ceased.

Unfortunately the -6volt supply failed and took this circuit out. all the DC coupled bi-polars transistors were changed except the dual n-channel JFET.

Now works, but the tuning voltage is to high, the first thoughts to increase the value of R63 which is a voltage dropper, since the current drawn by the two varactors is 1.82µA the resulting resister would be large.

The dual-gate n-channel JFET E412/U412 (Q1) is effectively being used as a fast analog switch, does anyone have any ideas how to alter the tuning voltage?

All suggestion would be very appreciated.

73’s
Mike G4WYZ
NB This has been a looooooong term project.

25th Feb 2018, 12:45 pm	#1
G4WYZ MikeyP Triode Join Date: Nov 2012 Location: Chorley, Lancashire, UK. Posts: 21	Racal 9081 phase detector problems. Phase Detector -again! The original fault on the Phase Detector was no varactor voltage, Q16 U898E was replaced with a 2N3819 resulted in the correct voltage tuning range of 3.6 – 14.8 volts. Then the flaky PSU folded again it had folded a number of times, although the 2N3055 always worked when tested, it was replaced with a new one and all the issued ceased. Unfortunately the -6volt supply failed and took this circuit out. all the DC coupled bi-polars transistors were changed except the dual n-channel JFET. Now works, but the tuning voltage is to high, the first thoughts to increase the value of R63 which is a voltage dropper, since the current drawn by the two varactors is 1.82µA the resulting resister would be large. The dual-gate n-channel JFET E412/U412 (Q1) is effectively being used as a fast analog switch, does anyone have any ideas how to alter the tuning voltage? All suggestion would be very appreciated. 73’s Mike G4WYZ NB This has been a looooooong term project.