On Jun 24, 2022, at 11:28 AM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:

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Welcome to my bench.? Today, we will look at demonic possession of a BFO.

Recap: BFO doesn't work with switch in any of the BFO positions.? Notice short note when switching from BFO modes to AM, right at make & break of rotary switch contacts? AM works normally.

Replaced Q6, subbed C166, C163, and even T11.? Removed both screws holding down the BFO board and they're clean on the underside.? Continuity to the chassis is good.? R124, 141 are good. Checked C168, 166 and 163 with cap meter and Sprague TO-6

The only way that I can get the BFO to come on and oscillate is by shorting the switch contact that feeds the AM detector's voltage divider to the other contacts.? When I do that, the set works normally with expected AGC behaviour in each position.? All points that should be at ground/chassis potential are where they should be.? The germanium diodes all measure around 0.230 V.? T11 adjusts the frequency and it's in the range (a scope probe pulls the frequency a couple of kHz).

C162 appears to be a base bypass.? Unfortunately for me I don't have another .05 ceramic cap at the moment but did try a .047 film cap, with no change. The switch has been cleaned.

What am I missing?? It's probably something dumb but I am just not seeing it!

TNX & 73,

Steve Wedge, W1ES/4

Time flies like an arrow.? Fruit flies like a banana.

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