Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jim on November 18, 2014, 09:53:23 pm
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I am looking into a buddy's Blues Jr which stopped playing--no blown fuse. The tubes were not glowing but 3.37V AC was present on each heater leg with the tubes in.
HV was good. Removing the tubes unbalanced the situation where 2.5V AC was on one side and 3.9V AC on the other. Also with the tubes out the pilot LED glows--with tubes in the LED does not glow. New tubes do not change a thing. Why won't the tubes light? Looks like a low current situation but I expect a little something. I am exited by the prospect of gutting this amp for the Doug's new boards but right now I just have to fix this thing. (plus my buddy is a cheap guy......) I feel like am misunderstanding something very basic. Any help is appreciated. Jim
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The tubes were not glowing but 3.37V AC was present on each heater leg with the tubes in.
The correct way to measure filament voltage is across the filament pins, not from each pin to ground. IOW, to measure the filament voltage for a EL84, put one meter probe on pin 4 and put the other meter probe on pin 5. What do you get when you do this?
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What he said ^
Also, if those Green leads really come to plug-terminals like the drawing implies, yank both connectors and measure what come out of the transformer, green-to-green. (Use Clip Leads!! Don't try to hand-hold meter probes on live parts, especially two live parts, especially floppy live parts.)