Rick May <[EMAIL PROTECTED]> made an utterence to the drakelist gang
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Hello Rien,
You were 100% correct. The problem was Q702, the dual gate FET on the 2nd mixer board. I place a small ferrite bead on the drain side of R712 and the oscillation disappeared. Strange that this would show up after using the radio for 24 years. Also strange is that the oscillation would not occur when the aluminum cover over the IF boards was removed. This made trouble shooting rather difficult. Thanks for the help.
73' Rick KC0HH Lamar, Co.
R.van Trotsenburg wrote:
"R.van Trotsenburg" <[EMAIL PROTECTED]> made an utterence to the drakelist gang ---------------------------------------------------------------------- Hallo Rick, I have had the same problem in my TR7. It was caused by a parasitic oscillation of the dual gate FET Q702 in the 2nd mixer board. It was resolved by inserting a small ferrite beat in the drain circuit of the FET. This does quiet down the FET, without effecting the rest of the amplifiers performance. The easy way to do this is by lifting the 68ohms resistor R712 at the drain side of the board and slipping a small ferrite bead (3x3mm) over the wire end and solder it back in the board. May be you have to use a new resistor because the wire end can be a bit short in length. After that the problem never appeared again in my TR7. In two other TR7's I have done this modification for preventive reasons. Let me know if you are successfull.
Rien PA0TRT
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