Does this circuit seem reasonable? - UK Vintage Radio Repair and Restoration Discussion Forum

Laurdys · 19th Dec 2015, 8:17 pm

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)

llama · 26th Dec 2015, 11:19 pm

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.
Graham

Peter.N. · 26th Dec 2015, 11:29 pm

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

Peter

Synchrodyne · 26th Dec 2015, 11:40 pm

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.

Cheers,

19th Dec 2015, 8:17 pm	#1
Laurdys Pentode Join Date: May 2009 Location: Stockton-on-Tees, County Durham, UK. Posts: 154	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) Attached Thumbnails __________________ If it can be built, it can also be fixed.

26th Dec 2015, 11:19 pm	#2
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	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. Graham __________________ Half my stuff is junk - trouble is, I don't know which half!

26th Dec 2015, 11:29 pm	#3
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	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. Peter

26th Dec 2015, 11:40 pm	#4
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	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. Cheers,