Fading Lamp?

[Packerswin14]

My home-built vibro champ seems to have developed an odd behavior.  After running for some time, the lamp goes out.  The amp still functions fine, but the lamp goes dim.  Shut it off, power it up again a while later, and the lamp burns bright again.  Leave it on for half an hour, and the lamp is out again.  The filament power comes from a PT I bought for this build, less than 15 hours on it, I'd say, including testing/startup and use.  Thanks, you guys are always helpful with the odd mysteries!

[HotBluePlates]

The amp still plays with the lamp out? Have you tried a new bulb?

How did you wire up the heaters and lamp? There are at least 2 ways, and if mixed, you might have problems.

[rafe]

When it goes out or dim take off the jewel and move the bulb around with your finger it should respond ...that will tell you that the bulb is not making good contact some of the new bulbs and perhaps some of the new sockets have very poor quality control. I used a NOS ge bulb to solve the problem in an amp of mine ...somebode else on the forum retensioned his....I hope that helps

[stratele52]

Check how many volts you have on your pilot lamp, bright and dim. Check also your tubes heater. You must have around 6.3 volts.  If your power transformer is not powerful enough the heater voltage drop under 6 volts

Or you have a bad solder on pilot lamp

[Willabe]

Someone here had this same problem a while back, turned out to be a bad -- new -- bulb. IIRC he got NOS USA made bulb and no more trouble.


                   Brad