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The power tubes will draw enough current to drag the B+ down considerably. The preamp tubes, well any tube really conduct current so there is a natural voltage drop acxross their plate loads. If a 12AX7 socket is left empty, no such current flows, and the full B+ voltage appears at the plate p-in. That will fall to normal once the tube is installed.
Agreed, keep quotes as small as possible, no need to copy my entire over-long paragraphs. I can't help myself typing them.
If disconnecting the pot let the voltage come back up to 47, then the circuit is loading the supply down. Got clip wires? Use one to clip the wire back onto the pot, or if it is wired back, that is OK too. So we are back down to 20 some? Measure voltage drop across the diode itself, and across that 470 ohm. We want to see if either of those is involved. I suspect not, but you never know.
Or we could insert a current meter between the wire and the pot to see what kind of current the circuit draws. The 20k divider out to draw maybe 2ma from the 47v. And we can remove the wire from the wiper and see if the voltage stays high, and also what range is at the wiper when unloaded.
What we are doing is trying to isolate the problem. We keep dividing things into this and that and see which parts are involved and which not. Eventually we narrow it down to exactly where the problem sits. Classic troubleshooting.
Agreed, keep quotes as small as possible, no need to copy my entire over-long paragraphs. I can't help myself typing them.
If disconnecting the pot let the voltage come back up to 47, then the circuit is loading the supply down. Got clip wires? Use one to clip the wire back onto the pot, or if it is wired back, that is OK too. So we are back down to 20 some? Measure voltage drop across the diode itself, and across that 470 ohm. We want to see if either of those is involved. I suspect not, but you never know.
Or we could insert a current meter between the wire and the pot to see what kind of current the circuit draws. The 20k divider out to draw maybe 2ma from the 47v. And we can remove the wire from the wiper and see if the voltage stays high, and also what range is at the wiper when unloaded.
What we are doing is trying to isolate the problem. We keep dividing things into this and that and see which parts are involved and which not. Eventually we narrow it down to exactly where the problem sits. Classic troubleshooting.
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