DSL50 Heater Problems

[dpm309]

I have a DSL50 that is having issues cutting out. Thought I fixed it a couple of years ago by cleaning all of the jacks, switches and beefed up the grounding on the 4/8 ohm outputs. I did notice that the heaters on V1 and V2 stopped glowing when it cut out. Tapping on the tubes brings them back up again so I am now thinking cold solder joint or something with the heater power supply for V1 and 2. This amp uses DC voltage for the heaters on 1 and 2 and AC on the rest of the tubes. Anyone ever run into this? Also for some reason I can't get the amp to cut out when I have the chassis upside down in my chassis cradle. Only cuts out when placed upright which makes me further think it could be a cold soldered joint. My next step is to pull the boards and check the solder joints.

[pompeiisneaks]

Sounds like a very good assessment.  Like you said, when you invert the chassis, the weight of the tubes on the socket could cause any bad solder connections to falter.  Quickly re-soldering the connections is an easy test and you can check if it resolves the issue.  I think its pretty common on the more sensitive stages to elevate the heaters on DC to get less chance of induced hum, so not shocking. The only other issue is that maybe the tubes you're seeing fail have issues in their heater elements, but I'd guess that's a lot less likely per your explanation. 

I've never run into this specific case but have just gotten done fixing a bad connection on one of my builds yesterday, and man it can be frustrating.

~Phil

[dpm309]

Found at least one cold joint on the bridge rectifier. Re-soldered all 4 legs and inspected the entire board for any more issues. Put it all back together and have been running it for about 30 minutes with no issues. Hope this does the trick.

[pompeiisneaks]

excellent news!