Mysterious power situation

[funkgang49]

Hope someone can help me figure out why my amps jewel light suddenly won't light up:
I sat down at my work bench this afternoon ready to continue working on a fuzz pedal circuit that I was working on yesterday and flipped on the power switch of my amp and the jewel light didn't come on as well as none of the tubes filaments lit up, hmm? Flipped it back off, standby was already in off position, and reached around to check the IEC power cable connection - it was ok however I noticed the rectifier tube was hot but not lit!? Rut-row! I unplugged everything and flipped over the chassis, drained the caps, pulled the fuses - they looked ok but I replaced them anyway - removed and replaced the jewel light bulb with a new one, popped in a different rectifier tube, and hooked-up my DMM to measure DC volts at each filter cap.

I turned on the power switch and all voltages are right on - all tubes lit up, flipped on the standby - amp sounds fine and is currently running no issues, sounds great. The jewel light, however, still won't light up?
Any ideas?

[xtian]

Have to suggest the obvious: check AC voltage at the lamp socket. This is a lamp powered by the heater circuit, right?

[funkgang49]

Yup, heater circuit.
It has been awhile since I've measured the AC - DMM to AC volts, Ground lead clipped to main chassis ground point, Hot lead to either filament leads from Power trans.?

[billyz]

I have had issues with the cheaper Chinese lamp assemblies. I only use the higher grade ones now, only cost a buck or so more.

[funkgang49]

Hey Billyz,
So you think it's just the lamp assembly?

I've had this one installed since Oct. 2014. Its from a batch of 5 or so that I bought about 6-7 years ago from C.E. Dist.

[Phil_S]

Yup, heater circuit.
It has been awhile since I've measured the AC - DMM to AC volts, Ground lead clipped to main chassis ground point, Hot lead to either filament leads from Power trans.?

No. To measure VAC, clip one meter lead to each filament lead. No ground involved. Your heaters aren't getting anything. Either it is the PT or there is a break in the filament circuit. It could be that one of the filament leads is somehow detached inside the transformer housing. Such a thing can be fixed.

[billyz]

CE Sells or used to sell both lamp assemblies, the cheaper chinese ones are the problem. It could be some other issue though. If its wired like a fender and the filament powers the tubes but not the lamp and the bulb is good, must be the lamp holder. I have no idea why the filaments did not light up at first . Check the the heater leads. Is the heater winding center tapped ? Filaments wired in series ? Maybe a shorted bulb at first and now its open so it lights up the rest of the filaments.

[funkgang49]

No. To measure VAC, clip one meter lead to each filament lead

Thanks Phil.

I measured 6.4vac which is right where it should be - installed new lamp assembly (Aeronautical Electr. Co.,Chicago-Billyz) and replaced bulb but still no lighty?

Attached is the spec. sheet for the Power Trans.

*Note; there is no Green/Yellow wire or Red/Yellow. The Green/White from Filament tap & Red/White from B+ are grounded at Main Power section ground point.

[John_P_WI]

What's the voltage at the lamp fixture?

You are sure the replacement bulb is good and 6.3 vac rated?

Most likely there is a bad solder / broken wire...

[funkgang49]

What's the voltage at the lamp fixture?

I measured the voltage at the fixture - juncture of transformer filament leads & filament heater wires to tube sockets. This connection is new since I installed the new lamp assembly.

I'll resolder each individual tube socket connections. Visual inspection everything looks good.

[Stevem]

I have had many a bulb ( even new )who's filament still looked 100% , but was open, so do not let that fool Ya !

If you have a seperate filament wire run to that lamp socket then the only other thing that could be taking place is that one of the wire terminations at the socket, or that socket wires feed end is only doing so by two strands of wire, or internally the wire is doing the same!
A meter only needs to pull very very little current for it to read and make you think all is well but the two strands of wire can not pass the needed current to power up the bulb !
I had a hard refresher lesson on this some 40 years ago with what I though was a failed electric fuel pump on my race car.
The pump would not work back at the fuel tank even though I had 12 volts showing up fine.
Then when I would spend 25 minutes ( 3 times over! ) to dismount the pump then hook the pump up across the cars battery it would run fine time after time!
In the end a bad frayed crimp connection that I had done in hurry was the cause!

[funkgang49]

Words of wisdom Steve - I will recheck and cut back wire ends as well as resolder!

Thanks!

[funkgang49]

You nailed it Steve! I had previously extended the filament leads from the transformer so I removed the shrink tubing, disconnected existing wire splices and recut, reconnected, and spliced in new leads and - voila!
Jewel light lights.

Thanks Steve!