Yep, meters use a calibrated voltage to measure resistors. The microcontroller computes Ohms Law and displays a value. Analog VTMM’s used high tolerance resistors/ammeter gauges and voltage to display a value. That’s why there’s so many ranges on the dial, unlike modern digital meters.
Are there any fasteners between the chassis and power transformer? If so, try tightening those too. Kinda have to get in there with all the wire attached still, but it can be done. I’ve heard worse transformer buzzing. It doesn’t sound like an overcurrent hum to me, so it’s probably fine. I would monitor the temps and let her rip. Luckily, you’re in contact with someone much more knowledgeable and experienced with Vox amps than I am. I think I recall Lyle talking about Vox iron kinda just doing that sometimes, depending on the manufacturer. Power transformers get very warm. Since you have other amps with similar sized iron(one with almost identical iron), it’s simple to compare temps. One of those inexpensive laser temp guns from Harbor Freight will work perfectly, or the thermocouple that came with your DMM if you have the patience for that.
Yeah I tightened the nuts holding the PT on, but I'm thinking I'm going to actually loosen it and see if it's mounted ok since it's not the original part maybe it was installed slightly weird. Yeah it gets warm for sure, but it doesn't feel more than I've experienced elsewhere so far. Not a bad idea to get the laser temp gun though!
@@YeatzeeGuitar Maybe some new hardware would help. I used some 10/32 bolts on an old Triad Tweed Super PT that was buzzing a little. The extra clamping force helped a lot. They barely fit. If you have some calipers, measure the mounting holes in the PT. Get the largest hardware that'll fit. Stainless is usually a little stronger than standard bolts of these smaller 8/32, 10/32 and 5mm sizes. Whatever you do, Don't drill out the holes and short the laminations to each other to make larger hardware fit. Learn from my stupid mistakes!.
@@matthewf1979 It is also worth mentioning that some Transformers will actually have a skinny cardboard tube surrounding the bolts that hold the transformer laminations together, so that the bolt doesn't short the laminations where it passes through them. If the Vox transformer here does not have any kind of insulator for those bolts perhaps they can be insulated with shrink-tubing before installation, if the hole diameter allows it.
For newbias and laypersons, the mention of "subtracting 5%" from the plate current figure when calculating where the bias sits is because the tube's "screens" dissipate a small amount of power, roughly 5%, that shows up in the measurement as part of the total tube current but doesn't actually affect the tubes' plate dissipation. Some people subtract it from the current (amperage) measurement beforehand (before calculating the wattage dissipation of the plate circuit), and some will subtract it from the final plate dissipation figure as was done here, but I don't think it makes a difference in terms of accuracy.
Is there aluminum foil tape on the side of that slider board that faces the output circuitry? It wouldn't hurt to add some shielding there if it's not already factory installed. Is there any aluminum foil inside the Vox cabinet to shield the preamp section? Because that's where you would get the most amount of noise radiated into the circuit if it isn't sufficiently shielded....
@@YeatzeeGuitar , remember that overlapping strips of aluminum foil tape have make electrical contact with each ( push a small Philips screwdriver into the seams and twist, to punch through the adhesive), and the foil has to contact the grounded chassis.
Love Rob Robinette's web site. It's a treasure trove of tube amp knowledge!
So helpful!
Yep, meters use a calibrated voltage to measure resistors. The microcontroller computes Ohms Law and displays a value.
Analog VTMM’s used high tolerance resistors/ammeter gauges and voltage to display a value. That’s why there’s so many ranges on the dial, unlike modern digital meters.
Makes perfect sense!
Are there any fasteners between the chassis and power transformer? If so, try tightening those too. Kinda have to get in there with all the wire attached still, but it can be done.
I’ve heard worse transformer buzzing. It doesn’t sound like an overcurrent hum to me, so it’s probably fine.
I would monitor the temps and let her rip. Luckily, you’re in contact with someone much more knowledgeable and experienced with Vox amps than I am. I think I recall Lyle talking about Vox iron kinda just doing that sometimes, depending on the manufacturer.
Power transformers get very warm. Since you have other amps with similar sized iron(one with almost identical iron), it’s simple to compare temps. One of those inexpensive laser temp guns from Harbor Freight will work perfectly, or the thermocouple that came with your DMM if you have the patience for that.
Yeah I tightened the nuts holding the PT on, but I'm thinking I'm going to actually loosen it and see if it's mounted ok since it's not the original part maybe it was installed slightly weird. Yeah it gets warm for sure, but it doesn't feel more than I've experienced elsewhere so far. Not a bad idea to get the laser temp gun though!
@@YeatzeeGuitar Maybe some new hardware would help. I used some 10/32 bolts on an old Triad Tweed Super PT that was buzzing a little. The extra clamping force helped a lot.
They barely fit. If you have some calipers, measure the mounting holes in the PT. Get the largest hardware that'll fit. Stainless is usually a little stronger than standard bolts of these smaller 8/32, 10/32 and 5mm sizes.
Whatever you do, Don't drill out the holes and short the laminations to each other to make larger hardware fit. Learn from my stupid mistakes!.
@@matthewf1979 It is also worth mentioning that some Transformers will actually have a skinny cardboard tube surrounding the bolts that hold the transformer laminations together, so that the bolt doesn't short the laminations where it passes through them. If the Vox transformer here does not have any kind of insulator for those bolts perhaps they can be insulated with shrink-tubing before installation, if the hole diameter allows it.
For newbias and laypersons, the mention of "subtracting 5%" from the plate current figure when calculating where the bias sits is because the tube's "screens" dissipate a small amount of power, roughly 5%, that shows up in the measurement as part of the total tube current but doesn't actually affect the tubes' plate dissipation. Some people subtract it from the current (amperage) measurement beforehand (before calculating the wattage dissipation of the plate circuit), and some will subtract it from the final plate dissipation figure as was done here, but I don't think it makes a difference in terms of accuracy.
Edit: "newbies," not"newbias". Facepalm!
@@goodun2974 Still works!
Is there aluminum foil tape on the side of that slider board that faces the output circuitry? It wouldn't hurt to add some shielding there if it's not already factory installed. Is there any aluminum foil inside the Vox cabinet to shield the preamp section? Because that's where you would get the most amount of noise radiated into the circuit if it isn't sufficiently shielded....
There is not, good tip!
@@YeatzeeGuitar , remember that overlapping strips of aluminum foil tape have make electrical contact with each ( push a small Philips screwdriver into the seams and twist, to punch through the adhesive), and the foil has to contact the grounded chassis.