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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 19th Dec 2015, 7:17 pm   #1
Laurdys's Avatar
Join Date: May 2009
Location: Stockton-on-Tees, County Durham, UK.
Posts: 154
Default Does this circuit seem reasonable?

I have a TV that I have previously tried to identify but to no avail (including a forum post) that has been got at in a massive way (almost nothing of the original circuit left). So I have been working on a circuit based on parts from other TV's I have circuits for, but I need to know if there are any problems with the circuit I have created. I have included circuit I've drawn as two *.PNG's (left and right half without overlap)
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If it can be built, it can also be fixed.
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Old 26th Dec 2015, 10:19 pm   #2
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Join Date: Jun 2006
Location: St Osyth, Nr Clacton, Essex, UK.
Posts: 1,327
Default Re: Does this circuit seem reasonable?

I admire your circuit drawing skills. Mostly I'm commenting to bump the enquiry. You ought to get more response in the TV section.

I don't understand all the semiconductor diodes at/near the front end but a TV expert would be better placed to comment. Similarly there's a semiconductor diode and half an EB91 feeding the audio output stage (maybe one for AGC and another for detection).

Can you connect it up stage by stage starting with the audio stage but taking care of all the heaters first?

I wish you good luck and hope someone else chips in.
Half my stuff is junk - trouble is, I don't know which half!
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Old 26th Dec 2015, 10:29 pm   #3
Join Date: Jul 2008
Location: Charmouth, Dorset, UK.
Posts: 3,497
Default Re: Does this circuit seem reasonable?

I can't see what some of these diodes do, what type of diodes are they? I too think your drawings are admirable.

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Old 26th Dec 2015, 10:40 pm   #4
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
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Default Re: Does this circuit seem reasonable?

On the audio side, it looks as if there is a semiconductor diode doing both the demodulation and AGC rectification jobs, followed by half an EB91 as the series noise limiter, highly desirable with AM at VHF. The AGC bias is fed back to the 1st (of two) EF80s in the audio IF chain, an example of AGC applied to a sharp cutoff valve.

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