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 Post subject: Re: Assistance requested with a superhet build.
PostPosted: Aug Thu 26, 2021 12:38 am 
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Joined: Mar Sun 22, 2020 5:56 am
Posts: 2041
Location: Arvada, CO, 80004
6BA7
6SB7Y
7Q7
5750
6WC5
5760

You can also probably use a 6AU6 in a Hartley configuration.

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 Post subject: Re: Assistance requested with a superhet build.
PostPosted: Aug Thu 26, 2021 9:40 pm 
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Joined: Nov Thu 04, 2010 5:49 am
Posts: 674
Location: Albany, NY
A 6AU6 as a mixer would be an autodyne mixer, right? I was reading about something like that earlier today.

I've come across two "interesting" superhet circuits that I can't quite figure out.

In the circuit below note the adjustable capacitor going from the first grid of the 6SK7 to the plate. The text explains that this is used to feedback some of the RF back into the grid creating a feedback loop and thus regeneration. R14, which is connected from the cathode bias resistor to ground, supposedly controls RF gain as well as regeneration once the set is in a state of regeneration. I've never seen this done before. Is this an actual valid solution or just one of those "what were they thinking?" ideas that appeared in radio experimenter magazines back in the day.

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The circuit below has a few things that I find strange. The mixer is made regenerative through what looks to be an electron coupled oscillator arrangement due to the tickler winding being made between the filament return and ground. The regeneration is being controlled through the screen grid voltage. I've seen reports of regenerative mixers but most of what I have heard is that they cause problems with pulling. However, these experiments generally involved the tickler coil being configured in an Armstrong configuration. Would this ECO arrangement cause less oscillator pulling?

The second thing that strikes me is the grid leak detector situated in front of the mixer. Wouldn't that cause detected audio to appear at the plate of the pentode section of the mixer? How would that get through the IF can?

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