Re: uBitx just started transmitting a loud hum #ubitx-help

 

James,

The hum you mentioned is in TX or RX mode ?

In RX mode there should be no DC voltages on Q6.

Raj

At 11/04/2018, you wrote:
Raj, just to clarify, that scope was on the collector of q6 with the 4v wave form. The base had only shown much less voltage. The collector had DC voltage as well (somewhere around 10v but I forgot to measure it exactly last night) which is about what I would expect.

The mic input to the base of q6 does have DC of around 1 or 2V again I didn't measure it exactly as it looked about right for the voltage divider bias made up of r61 and r62.

As pointed out, there may well be a grounding issue elsewhere, which would/may explain hearing audio on transmit at the beginning, but at least the culprit for the hum was related to the electret mic.

Just to clarify, haven't measured current of rig yet on tx but it is less than 3A as my fuse is intact.

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