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PostPosted: 20 Jun 2015, 05:14 
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Hi, 1st post here, I've done some work with valves before - but mainly by following instructions, so I'm not very experienced.

I've built the kit (with all the supplied parts) but I'm not getting a peep of a sound out of it on either channel. My input is my mobile phone, which is supplying a measured (multimeter) voltage of 100-150mV - so I'm pretty sure i have a workable input.

The batteries are all new and I'm measuring 3.1V from the AAs and 18.9V from the PP3s.

Both LEDs are lit but I'm only getting 1.04V on the heater supply. Is that too low for operation? The both LEDs have 1.7V.

There is no sound at all even from light contact on the valves.

Any help appreciated.


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PostPosted: 21 Jun 2015, 23:09 
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Check the voltage across the chip.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 22 Jun 2015, 04:56 
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Looking from the bottom of the board I have:

0.72 0 0 18.7

0 0.72 0 0

That would put the 18V on an unused pin? The little notch on the op amp is on the side away from the AA batteries?


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PostPosted: 22 Jun 2015, 05:13 
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There we no unused pins. You may have the chip in backwards.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 22 Jun 2015, 07:55 
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I tried turning the chip around and switched the amp on and the op amp chip got very hot very quick!


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PostPosted: 22 Jun 2015, 16:44 
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I guess it was in the right way. I would have checked the voltage across pin 4 and 8 first to see if there was 18V. Are the tubes in the right way. The red dot should go to the square solder pad. Check this time before switching. Also check the electrolytic caps are in the right way. I have found if they are are not they act like a short cct.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 23 Jun 2015, 12:29 
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The valves are both in the correct way round and I'm pretty sure the electrolytic caps are the correct way round (the black line indicating negative are all pointing in the same way on the board.

You can see the red dot on the tubes and some of the caps on the photo


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PostPosted: 23 Jun 2015, 17:35 
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Tubes look right. Have you re-checked component on PCB to schematic. Are the right parts in the right spots?

These usually work first time. On the input have got the hot wire and earth round the right way?

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 27 Jun 2015, 07:46 
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I ordered some new op amps and when i replaced the one that was supplied with a new one it worked first time!


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PostPosted: 27 Jun 2015, 07:49 
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Mannakin wrote:
I ordered some new op amps and when i replaced the one that was supplied with a new one it worked first time!

I'm so glad you have to going. Not hard to imagine a faulty OPAMP.

So what do you think?

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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