Final check not happening

[harrislp]

I'm guessing the voltage at T5 is now higher than it should be?

No, it is still reading 84V, same as it was before. terminal 1 is still 154V though.

 

[harrislp]

I switched the diodes around and the same diode that wasn't working before is now not working in the other position, so I guess I have a dead diode. I have emailed Eileen asking for a couple of new ones, is this the correct protocol?

 

[harrislp]

Hello, I'm back again!  8)

Got the replacement LEDs (thanks Eileen for your excellent service) and soldered them in, they both lit up. Excellent. I measured all the voltages and they checked out, did the voltage check on the headphone jack and it was fine. Then I went back and checked the resistances and they all checked out, except the ones with the star in the manual (1,2,4,5 and 13) all showed O.L (outside limits). All the other resistances checked out.

Should I be worried about this, or is it okay? I need to be sure before I plug any headphones in, i'm paranoid after I burnt out a driver in my Beyers after not properly checking the output voltage of the headphone jacks after the initial build.  :'(

Thanks,

harris.

 

[ssssly]

If the voltages on the tubes check out you should be fine.

Enjoy some tunes.

 

[harrislp]

I plugged in some headphones and it worked great for a bit but then it felt weird, like the headphones were getting voltage or something, the same as it did when I burnt out the driver. I turned it off and tried to turn it back on again but the LED has stopped working, on the A8 pin as it did before. I still have one spare LED but I don't want to put it in just so the whole thing happens again. Is it plugging in the headphones that is causing the LED to short out? It was working okay before I plugged in the headphones. The voltages are back to how they were before I replaced the faulty LED (see earlier post), so there's definitely something wrong. It's  lucky I live on the ground floor or else this thing would be in many many pieces. What am I doing wrong that this thing will not work! Very frustrated. What should I try next?

 

[Paul Birkeland]

So terminal 1 now has high voltage again?  Do both sides of the 12AU7 glow?  If one of the LED's isn't lighting, then either that side of the tube isn't getting heat, the LED isn't properly soldered, or the 22K resistor between T1 and T2 isn't properly soldered.

Plugging in the headphones will have no influence on the LED's, the headphone output it on the opposite side of the circuit, isolated by the 6080 and coupling caps. 

I wouldn't just replace the LED again, there is some evidence that this wasn't the problem to begin with.  Check the connections and components that go to A4/5, A6, A7, and A9.

 

[harrislp]

I took a picture of the unit when it is on. I don't think the 12AU7 is working properly, there were two filaments that lit up before the LED blew out but now that doesn't seem to be the case. I'll try reflowing and resoldering again after work and see how that goes, but this one is the most puzzling to me of the myriad problems I've had with this thing. It seems to work for a bit and then get overloaded or something. Thanks for your help, hopefully it's just another soldering issue.



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[Doc B]

Try pulling the 12AU7 tube and measuring resistance across pin 4 and pin 9, and then across pin 5 and pin 9. Those are the two halves of the heater. Each should read low ohms.

 

[harrislp]

I got around 6.5 ohms each for these two measurements, Doc. I assume that's normal?

 

[Doc B]

Yeah, that means the tube heater is OK. So if one half is not lighting there may be an issue with the tube socket or the wires connected to pins 4,5 and 9. Or the heater might be working OK and just looks odd. The next check should be to see if you measure 6 volts or so from B4 to B9 and from B5 to B9.