Re: {Collins} 75s1 PS Hum



If you are using a relatively new set of head phones to do your listening with - it might be the head phones. Many of the new ones will hear all the way down to 30 cycles or so. Way below what that radio was designed for. Therefore, you are listening to what is normally there anyway.

If so, try a speaker that was designed for the radio - the low cutoff will usually be several 100 cycles.

I have been trapped by that problem several times!

Howard K5JCP

On 10/12/2017 10:57 AM, Karl Bridges via Collins wrote:
I'm fighting the same issue in a non-Collins receiver right now. It's been
suggested it might be a tube short so start substituting tubes one by one
going back from the end of the audio chain until the issue resolves. And I
assume all the PS caps are correctly installed.

On Thu, Oct 12, 2017 at 8:29 AM, George Cortez via Collins <
collins@xxxxxxxxxxxxx> wrote:

I continue to work on the 75s1. It has some hum on rx. I replaced all the
power supply caps with sprague atoms. The hum persists. Any other ideas?
Perhaps some electrolytics down the audio chain?
George NE2I
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