First Radio Build - 12V HT system - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

Herald1360 · 2nd Aug 2017, 5:47 pm

6 (+ve) looks OK. 5 (output) looks bad, should be around half rail. Has the capacitor between it and the speaker been missed out? Connecting direct through speaker to ground could explain.
7 (Bypass) is plausible.

http://www.ti.com/lit/ds/symlink/lm386.pdf

bobskie · 2nd Aug 2017, 6:43 pm

I just checked and it's definitely connected to the 100uf electrolytic. It still reads at 0.60V.

Cameron

Herald1360 · 2nd Aug 2017, 8:54 pm

Hmm, circuit of LM286 stage? Is the biassing right?

Could just be knackered chip.

bobskie · 2nd Aug 2017, 9:32 pm

So should I just do a final check if my wiring then if nothing is wrong buy a new chip? Or is there anything else I can measure first.

Herald1360 · 3rd Aug 2017, 12:44 pm

A careful measure of every voltage on the LM386 pins might help.

A circuit showing us how you think it's connected up would be useful. The TI link I posted yesterday shows one way it could be connected up and work OK.

kalee99 · 3rd Aug 2017, 5:02 pm

Hi All,
This is the circuit I use for radio circuits. It keeps the rf well away from the amplifier.
Paul.

bobskie · 3rd Aug 2017, 8:07 pm

Quote:

Originally Posted by Herald1360

A circuit showing us how you think it's connected up would be useful. The TI link I posted yesterday shows one way it could be connected up and work OK.

It's connected up following the pin numbers on the document you send and using the circuit diagram I attached a few pages back. I will measure the voltages tommorow. It's probably something stupid but I'm new to building circuits rather than just repairing things following a guide. I have built a few things but this is the most complex. I really hope I can get it working

. Thanks for your help,

Cameron

bobskie · 3rd Aug 2017, 8:09 pm

Quote:

Originally Posted by kalee99

This is the circuit I use for radio circuits. It keeps the rf well away from the amplifier.

I'll keep that in mind for if I can't get this one working, it does look fairly similar to the one I'm using. Thanks for your help,

Cameron

bobskie · 5th Aug 2017, 6:10 pm

I got the voltages measured today with my new fluke 25

Here are the results:

Pin 1-1.28V
Pin 2-0V
Pin 3-0.053V
Pin 4-0V
Pin 5-0.60V
Pin 6-12.18V
Pin 7-6.37V
Pin 8-1.63V

I have attached another copy of the circuit diagram I used. Thanks for the help,

Cameron

2nd Aug 2017, 5:47 pm	#61
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: First Radio Build - 12V HT system 6 (+ve) looks OK. 5 (output) looks bad, should be around half rail. Has the capacitor between it and the speaker been missed out? Connecting direct through speaker to ground could explain. 7 (Bypass) is plausible. http://www.ti.com/lit/ds/symlink/lm386.pdf __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

2nd Aug 2017, 6:43 pm	#62
bobskie Hexode Join Date: Apr 2017 Location: Falkirk, Stirling, UK. Posts: 336	Re: First Radio Build - 12V HT system I just checked and it's definitely connected to the 100uf electrolytic. It still reads at 0.60V. Cameron

2nd Aug 2017, 8:54 pm	#63
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: First Radio Build - 12V HT system Hmm, circuit of LM286 stage? Is the biassing right? Could just be knackered chip. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

2nd Aug 2017, 9:32 pm	#64
bobskie Hexode Join Date: Apr 2017 Location: Falkirk, Stirling, UK. Posts: 336	Re: First Radio Build - 12V HT system So should I just do a final check if my wiring then if nothing is wrong buy a new chip? Or is there anything else I can measure first.

3rd Aug 2017, 12:44 pm	#65
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: First Radio Build - 12V HT system A careful measure of every voltage on the LM386 pins might help. A circuit showing us how you think it's connected up would be useful. The TI link I posted yesterday shows one way it could be connected up and work OK. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

3rd Aug 2017, 5:02 pm	#66
kalee99 Rest in Peace Join Date: Dec 2004 Location: Newcastle Upon Tyne, Tyneside, UK. Posts: 420	Re: First Radio Build - 12V HT system Hi All, This is the circuit I use for radio circuits. It keeps the rf well away from the amplifier. Paul. Attached Thumbnails

5th Aug 2017, 6:10 pm	#69
bobskie Hexode Join Date: Apr 2017 Location: Falkirk, Stirling, UK. Posts: 336	Re: First Radio Build - 12V HT system I got the voltages measured today with my new fluke 25 Here are the results: Pin 1-1.28V Pin 2-0V Pin 3-0.053V Pin 4-0V Pin 5-0.60V Pin 6-12.18V Pin 7-6.37V Pin 8-1.63V I have attached another copy of the circuit diagram I used. Thanks for the help, Cameron Attached Thumbnails