Tubes do not glow anymore [resolved]

[Edhead]

Hello,

I am looking for some advice for my issue where the tubes don't glow anymore.

My 3.0 kit has been working for a few months now. But about 2 months ago, there was one time where the tubes didn't glow when I turned on the switch. I just toggled the switch again and then it worked. I didn't pay much attention and then moved on. Then 2 weeks ago, it happened again but this time it took multiple tries to toggle the switch to have it working again. Then a few days ago, while I was listening to my music with it, all of a sudden the volume was fading to 0 within a couple seconds and the tubes stopped glowing. Now I am not able to have the tubes working.

This morning I took a closer look at the wiring. I use a tweezer to tab all the connection points and everything seems very solid to me. I check the resistance again according to the manual and the readings are all good. I was planning to check the voltages, but it seems like one of the requirements is to have the tubes glowing first, so I didn't proceed with the voltage check.

The fuse was not blown. I also tried swapping the tubes but no luck. Would it be possible that the tubes themselves failed?

Any advice would be much appreciated! Thanks!

Ed

[Paul Birkeland]

Can you post some build photos? 

The glowy bits inside the tubes are fed by pins 1 and 12 on each socket, and this comes from the H terminals at the back of the amp.  You may have a loose connection somewhere in that chain, or possibly a loose connection from the incoming mains power.

[Doc B.]

One possibility is the power switch was damaged from too much heat during soldering. With the amp unplugged from the AC mains wall outlet you can take a multimeter set to the ohms scale and put one probe on each terminal on the power switch. Switched to the off position it should read infinite resistance across the terminals and switched on it should read very low resistance like a few ohms. If you get that low resistance in the on position as expected, try gently wiggling to switch rocker side to side and see if the reading jumps to infinity and back to a low reading. That would indicate that the switch overheated during soldering and the contacts inside are a little loose. In that case replacement is the best bet. You can order a switch from the online store. If the reading holds at a low resistance in the on position even with a tiny bit of side to side wiggling of the rocker the switch is OK.

[Edhead]

Thanks for the quick response, Paul and Doc! I didn't expect a reply on a Saturday!

I checked the switch and I got infinity when it's off and 0 ohm when it's on. The reading did jump a bit a couple times while it's On but I think that's due to the movement of the probes as I don't have the clip style probes. So I guess it's not the switch.

Attached are some photos of my build. Please let me know if there is any particular area I should be focusing on. Thanks!

Ed

[Natural Sound]

A few things you can check while waiting for PB and Doc B to get back with you. Do you have enough solder on the MBRF745 diodes (H2L to H7L)? There isn't a good camera angle that shows this area clearly. These diodes rectify the DC for the heaters. You also might want to check the connections on the 5W resistor on 30L and 31L.

Good luck!

[Paul Birkeland]

What are your voltages on H2, H5, H4, and H7, 30, 31, 32?

[Edhead]

Thanks Natural Sound!

I double checked the connections you mentioned and noticed 30L has enough solder but it's broken off though. When I pushed the 5W resistor a bit, I could see the pin and the solder moving away from the plate!

I soldered 30L again and it's working again now Thanks everyone for your help. Much appreciated!

Ed

[Natural Sound]

Good job!. I'm glad you are making music again.