Peavey Butcher, no heater voltage!

[Mr_bibbles]

Hey Y'all-

I have a fairly simple issue (No heater voltage on either pre or power tubes) on a Peavey Butcher that's stumping me. As I understand, it's a normal 6.3vac heater that's elevated via the +26 supply.

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Unplugged the Power supply connections so that it was isolated from the pre/pwr amps, and whala I get good 6.3vac across the molex connector, so we know it's coming out of the transformer, passing the fuse, and reaching the molex send.

BUT when I hook it up to the rest of the tubes, the AC voltage drops to 0. I've tried everything hooked up, power board only hooked up, and preamp board only hooked up. In each case I still read 6.3VAC across the fuse, but at the molex connector I get 0.0VAC, with proper elevation at 26+. I disconnected the hum balance circuit on the power board, no change. I've tried with tubes in and out. What the heck could be going on here? Perhaps there is a direct short that only affects AC leaking through the elevation circuit?

Thanks for your time!

[Jon Snell]

Not a short, the opposite. Check where the Fil voltage stops and there will be your bad connection.
Carry on from where you started and with one test lead/6volt test lamp follow the circuit to each point and see where the voltage stops.

[Mr_bibbles]

Jon! Thanks for replying. First, a 6v test lamp? Like, a 6v battery in series with a bayonette lamp or something? Is that to apply 6v directly to the boards isolated from the supply?

Secondly, that's what my thought was too, but the voltage stops at the molex connector ONLY when it's connected to the other boards. If the molex is unconnected, we have 6.3VAC across it, but as soon as you connect it to anything the voltage is shorted to ground. How could I further check continuity of the heater circuit? I'm guessing that's where the lamp comes in but I'm a little foggy on exactly how to further isolate the issue.

[Enzo]

Look in the molex pin females, are any spread wider than normal? ANy look darkened? Your 6vAC comes in from the transformer to the power supply board, then through the fuse and right back off the board. Check the wires over to the power tube board, check at both ends.

[Enzo]

Going to zero does not mean shorted. Shorted would blow fuses. It means you have an open somewhere in that circuit.

[Mr_bibbles]

Enzo! Thanks for replying. I could be totally wrong here, but because I was able to measure 6.3VAC from heater ---> ground, wouldn't that imply that there is a short to ground? Err... I guess it wouldn't be a true 'short', but I do have a flow of 6.3VAC to ground.

Also, I connected two different discreet wires directly to the male molex send pins and ran them out like that to the two different boards with the same results., so I'm pretty sure that eliminates the actual molex connector as a suspect....

[Mr_bibbles]

Other important info:

I've also disconnected the elevation circuit via the 4.7K resistor, the elevated DC disappears but the 0VAC stays. I've tried different wires to and from the filament sends, replacing the center tap capacitor, disconnecting the hum balance pot, trying to power each board independently, with and without tubes installed...

[Jon Snell]

Jon! Thanks for replying. First, a 6v test lamp? Like, a 6v battery in series with a bayonette lamp or something? Is that to apply 6v directly to the boards isolated from the supply?

Secondly, that's what my thought was too, but the voltage stops at the molex connector ONLY when it's connected to the other boards. If the molex is unconnected, we have 6.3VAC across it, but as soon as you connect it to anything the voltage is shorted to ground. How could I further check continuity of the heater circuit? I'm guessing that's where the lamp comes in but I'm a little foggy on exactly how to further isolate the issue.

I use a 6volt pilot lamp. The power is your heater voltage, when the lamp is out, no voltage and move nearer to the fuse end of the heaters. Place the lamp across the heater supply leads.

[Dave H]

Also, I connected two different discreet wires directly to the male molex send pins and ran them out like that to the two different boards with the same results., so I'm pretty sure that eliminates the actual molex connector as a suspect....

Did you check for bad solder joints on the Molex?

[Enzo]

6v to ground??? What matters is 6v ACROSS the heater, not to ground.

[Mr_bibbles]

Word! I was getting 0 Across but.... I'm an idiot and the fuse was bad the whole time. Not sure how it slipped by as I definately measured it... maybe there's something distracting happening today?? Nothing comes to mind Sorry to have wasted your time! Thanks guys!

[J M Fahey]

I use a 6volt pilot lamp. The power is your heater voltage, when the lamp is out, no voltage and move nearer to the fuse end of the heaters. Place the lamp across the heater supply leads.

That.
You need a load to significantly test that hater supply.
A dirty/corroded/very loose male/female connector pair with, say, 1k resistance , will pass 6V intact ... to a 10M input multimeter.

Draw 100 mA to 2A and voltage drops to almost 0

[Enzo]

Did you measure the fuse while it was still in the clip? That will show a false reading.

[g1]

I still read 6.3VAC across the fuse,

Well, you had it already in your first post. A good fuse will not have voltage across it. Sorry, I just got here or I would have said something.

[Jazz P Bass]

Standard electric test of the fuse circuit.
If you measure a voltage across the fuse then it is open circuit.