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July 21, 2010 - 3:37pm
#1
My valves just went cold!
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Off top of my head, blown fuse or blown transistors. Is the power cord plugged in all the way?
Thanks geoff, but the amp still has power - indicator light and vu meter still working, just the valves wont warm up
To start off, do the filaments light? If not I would trace the filament circuit back to the power supply, and check for opens. If the filaments light, I would check the B+ supply for high voltage and possible open circuit.
Cheers.
thanks steve,no the filaments don't light up,when it happened as the sound died away the filaments went out - I do have a spare amp ,and i'll check out the circuits asap
One of my favorite webpages - no longer available - was titled "Experiments in Electrocution".
When you begin tracing circuits do remember there has been as much as 650V coursing through a tubed amplifier. Tube amps can hold that voltage for quite a long time. Remove any rings, don't touch anything if you don't know what it is you're touching and whether or not it can bite you, never touch across two components or one component to chassis ground and keep one hand in your pocket at all times - this is important, don't give the voltage a clear path from one hand to the other through your chest and across your heart. Never put your hand inside an amplifier that is powered up. You might want to have someone standing by if you get into the amp. If you get shocked and held there, tell them not to grab you or they will become part of the circuit. Give them a 2X4 and tell them to use it to knock you off the amp if the worst happens.
http://antiqueradio.org/dimbulb.htm
Check first for internal fuses. All the above precautions apply when you reach into an amp for a blown fuse.
thanks jan, I did carefully pull the amp apart after 24 hrs. Could'nt see any visual clues - burnt area etc...My skills don't extend to checking with multimeter etc, so this amp will end up as landfill, as I have 2 spares ( last 2 units in shop paid $50 each) You gets what you pay for!!! Will look for a decent old marantz etc in 2nd hand shop.
Sorry to hear of the demise and no repair, but quite understandable. Hope things go well looking for the Marantz.
Cheers.
The only reasons I can guess as to why all filaments would fail to illuminate but other circuitry appears to come alive would be if the filament transformer failed (unlikely) or if the filaments are wired in series and one failed (much more likely). Take the tubes to a shop with a tube tester to find the culprit (or eliminate this theory).
Into the wayback machine, Sherman, we have to make good time to find this device.
Ok, to avoid the PITA of finding a tube tester, you can just get an ohmmeter and check for continuty on the filament pins. The pinouts may be found here - http://bustedgear.com/res_Tube_pinouts.pdf.