Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is, “ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.” I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input. I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro Sent from my iPhone
Hi Mauro, If it all works fine on the bench then the setup in the machine must be the problem. Check that the volume control box and the mechanism chassis aren't 'Hot' - connected in some way to the 'mains! Set your meter on AC volts suitable for your line power and touch one lead to the volume control box and the other to earth ground. Should not be over a few volts leakage no matter which way the power plug (if reversible) is inserted. If good then check the metal chassis, as well as the tone arm and amplifier. Here is a link to make a simple leakage detector which is a step up from the above crude test procedure. 🔗 https://www.flippers.com/pdfs/ElectricalSafety/Electrical_Safety_Testing.pdf <https://www.flippers.com/pdfs/ElectricalSafety/Electrical_Safety_Testing.pdf> John :-#)# On 2026-07-29 4:21 p.m., M De Simone via Jukebox-list wrote:
Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
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-- John's Jukes Ltd. 7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 Call (604)872-5757 (Pinballs, Jukes, Video Games) flippers.com "Old pinballers never die, they just flip out"
On 7/29/2026 7:35 PM, John Robertson via Jukebox-list wrote:
Hi Mauro,
If it all works fine on the bench then the setup in the machine must be the problem.
Check that the volume control box and the mechanism chassis aren't 'Hot' - connected in some way to the 'mains!
Set your meter on AC volts suitable for your line power and touch one lead to the volume control box and the other to earth ground. Should not be over a few volts leakage no matter which way the power plug (if reversible) is inserted. If good then check the metal chassis, as well as the tone arm and amplifier.
Here is a link to make a simple leakage detector which is a step up from the above crude test procedure.
🔗 https://www.flippers.com/pdfs/ElectricalSafety/Electrical_Safety_Testing.pdf <https://www.flippers.com/pdfs/ElectricalSafety/Electrical_Safety_Testing.pdf>
John :-#)#
I don't like the idea of the loading resistor in that tester. I've had chassis that give that little *buzz* shock when touching the juke and the resistor can ground that out. When I've ran into the hardly noticeable buzz, I'll measure from ground to the chassis. The buzz some of us feel sometimes can be "shorted out" by simply grabbing onto the machine instead of just your fingertips or whatever body part is barely touching the machine using a cheap DMM without enough ohms/volts. I've been there and done it. I now always use one of my higher end meters to do that test. Often the chassis to a real ground is as high as the line voltage, yet not give a hell of a shock. It's so mild that your body's conductance to ground can *short* it down close to zero, yet unnerving to others. The cheap meter can measure close to zero volts from chassis to ground, but a good meter can measure as high as line voltage.
On 2026-08-02 5:39 a.m., Tony Miklos via Jukebox-list wrote:
On 7/29/2026 7:35 PM, John Robertson via Jukebox-list wrote:
Hi Mauro,
If it all works fine on the bench then the setup in the machine must be the problem.
Check that the volume control box and the mechanism chassis aren't 'Hot' - connected in some way to the 'mains!
Set your meter on AC volts suitable for your line power and touch one lead to the volume control box and the other to earth ground. Should not be over a few volts leakage no matter which way the power plug (if reversible) is inserted. If good then check the metal chassis, as well as the tone arm and amplifier.
Here is a link to make a simple leakage detector which is a step up from the above crude test procedure.
🔗 https://www.flippers.com/pdfs/ElectricalSafety/Electrical_Safety_Testing.pdf <https://www.flippers.com/pdfs/ElectricalSafety/Electrical_Safety_Testing.pdf>
John :-#)#
I don't like the idea of the loading resistor in that tester. I've had chassis that give that little *buzz* shock when touching the juke and the resistor can ground that out. When I've ran into the hardly noticeable buzz, I'll measure from ground to the chassis. The buzz some of us feel sometimes can be "shorted out" by simply grabbing onto the machine instead of just your fingertips or whatever body part is barely touching the machine using a cheap DMM without enough ohms/volts. I've been there and done it. I now always use one of my higher end meters to do that test. Often the chassis to a real ground is as high as the line voltage, yet not give a hell of a shock. It's so mild that your body's conductance to ground can *short* it down close to zero, yet unnerving to others. The cheap meter can measure close to zero volts from chassis to ground, but a good meter can measure as high as line voltage.
The test was designed to show if the voltage leakage was potentially (yeah, I know!) dangerous to the consumer, not if you just got a slight tingly buzz. I consider the test to be an excellent safety test to see if a chassis is 'hot' enough to risk a serious/tragic shock. Note it was professional Electrical Engineers who made this test, I trust their reasoning in the matter of electrical safety. I have a Hi-Pot tester in my shop that we use to check line powered equipment to see if they can trip the safety switch when 1500VAC is resented to the power cord and all exposed metal is checked with the probe. Not everyone has this expensive tool so I consider the resistor test as the next best one... Some light reading (check page 33): https://www.psma.com/sites/default/files/uploads/estguide2.pdf John :-#)# -- John's Jukes Ltd. 7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 Call (604)872-5757 (Pinballs, Jukes, Video Games) flippers.com "Old pinballers never die, they just flip out"
Check with Bill Bickers. He will probably tell you resistor(s) On Wed, Jul 29, 2026 at 7:22 PM M De Simone via Jukebox-list < jukebox-list@lists.netlojix.com> wrote:
Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
Sent from my iPhone _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
I seem to remember there's two versions of that amp. One has the volume control built into the amp itself and is a pain to adjust because it's down near the floor. I've seen where someone modified the machine by adding the separate volume control box in order to make adjusting the volume easier. If your back door has a crude cutout for the volume control, this is probably the case. On Wednesday, July 29, 2026 at 07:22:06 PM EDT, M De Simone via Jukebox-list <jukebox-list@lists.netlojix.com> wrote: Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is, “ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.” I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input. I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro Sent from my iPhone _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox. As for the gutted volume control, it's the way to go when installing a light weight ceramic cartridge. Some add a resistor and a cap in the pico farad range but I haven't heard a difference with or without them. I've seen them with a pot of anywhere between 10K and 100K. Tony On 7/29/2026 7:21 PM, M De Simone via Jukebox-list wrote:
Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
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Appreciate this response, if the hum persists we will try your recommendation. It will be a few weeks before I can get the amp back to the jukebox, out of town. Although, I’m still curious why I would read 23 vac on the chassis with my Fluke multimeter and less than 1 vac with my 1000 ohms / volt Simpson analogue meter? I’ve done this comparison before when calibrating my tube tester and the difference was minimal? Sent from my iPhone
On Aug 2, 2026, at 7:40 AM, Tony Miklos via Jukebox-list <jukebox-list@lists.netlojix.com> wrote:
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox.
As for the gutted volume control, it's the way to go when installing a light weight ceramic cartridge. Some add a resistor and a cap in the pico farad range but I haven't heard a difference with or without them. I've seen them with a pot of anywhere between 10K and 100K.
Tony
On 7/29/2026 7:21 PM, M De Simone via Jukebox-list wrote: Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
Sent from my iPhone _______________________________________________ Jukebox-list mailing list --jukebox-list@lists.netlojix.com To unsubscribe send an email tojukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives:http://jukebox.markmail.org/
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On 8/2/2026 8:42 AM, M De Simone via Jukebox-list wrote:
Appreciate this response, if the hum persists we will try your recommendation. It will be a few weeks before I can get the amp back to the jukebox, out of town. Although, I’m still curious why I would read 23 vac on the chassis with my Fluke multimeter and less than 1 vac with my 1000 ohms / volt Simpson analogue meter? I’ve done this comparison before when calibrating my tube tester and the difference was minimal?
Sent from my iPhone
I've looked before but not found anything on the internet explaining ohms/volt in a meter. As I was taught is that all volt meters draw a very slight current from the voltage you are measuring, putting a very slight load on the voltage. The AC you are reading isn't direct AC from the line voltage, it is from induction, so it can "provide"? only a very low current. Your Simpson puts a larger drain on the circuit and loads it down. DMM's in general have a higher ohms/volt, so it doesn't load the voltage as much. But a lower quality DMM will still have less ohms/volt than a high quality DMM. I recall one time working on a much newer, but tube Wurlitzer amp using a cheap DMM. At first the voltage across a capacitor would read a certain voltage, but it was a very touchy circuit so the load from the meter quickly lowered the voltage, drawing the capacitors voltage down. I hope that makes any sense and I don't have too many errors. This makes me wonder what happened to my father's tube type voltmeters? Tony Aug 2, 2026, at 7:40 AM, Tony Miklos via Jukebox-list <jukebox-list@lists.netlojix.com> wrote:
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox.
As for the gutted volume control, it's the way to go when installing a light weight ceramic cartridge. Some add a resistor and a cap in the pico farad range but I haven't heard a difference with or without them. I've seen them with a pot of anywhere between 10K and 100K.
Tony
On 7/29/2026 7:21 PM, M De Simone via Jukebox-list wrote: Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
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Tony, Yes it does make sense. Since the recommendation is for a 1000ohms/volt I’m going with the Simpson meter results. Thanks again, Mauro Sent from my iPhone
On Aug 2, 2026, at 12:44 PM, Tony Miklos via Jukebox-list <jukebox-list@lists.netlojix.com> wrote:
On 8/2/2026 8:42 AM, M De Simone via Jukebox-list wrote: Appreciate this response, if the hum persists we will try your recommendation. It will be a few weeks before I can get the amp back to the jukebox, out of town. Although, I’m still curious why I would read 23 vac on the chassis with my Fluke multimeter and less than 1 vac with my 1000 ohms / volt Simpson analogue meter? I’ve done this comparison before when calibrating my tube tester and the difference was minimal?
Sent from my iPhone
I've looked before but not found anything on the internet explaining ohms/volt in a meter. As I was taught is that all volt meters draw a very slight current from the voltage you are measuring, putting a very slight load on the voltage. The AC you are reading isn't direct AC from the line voltage, it is from induction, so it can "provide"? only a very low current. Your Simpson puts a larger drain on the circuit and loads it down. DMM's in general have a higher ohms/volt, so it doesn't load the voltage as much. But a lower quality DMM will still have less ohms/volt than a high quality DMM. I recall one time working on a much newer, but tube Wurlitzer amp using a cheap DMM. At first the voltage across a capacitor would read a certain voltage, but it was a very touchy circuit so the load from the meter quickly lowered the voltage, drawing the capacitors voltage down.
I hope that makes any sense and I don't have too many errors.
This makes me wonder what happened to my father's tube type voltmeters?
Tony
Aug 2, 2026, at 7:40 AM, Tony Miklos via Jukebox-list <jukebox-list@lists.netlojix.com> wrote:
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox.
As for the gutted volume control, it's the way to go when installing a light weight ceramic cartridge. Some add a resistor and a cap in the pico farad range but I haven't heard a difference with or without them. I've seen them with a pot of anywhere between 10K and 100K.
Tony
On 7/29/2026 7:21 PM, M De Simone via Jukebox-list wrote: Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
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On 2026-08-02 11:12 a.m., M De Simone via Jukebox-list wrote:
Tony, Yes it does make sense. Since the recommendation is for a 1000ohms/volt I’m going with the Simpson meter results. Thanks again, Mauro
The MINIMUM is a 1,000 Ohms/Volt meter. This loads the circuit more than a modern DMM so 1000R/V will be the worst case test using the recommended resistor in the Motorola safety check. electronics.stackexchange.com Why is analog "voltmeter sensitivity" is defined as ohm/Volt? <#> What is the motivation to define a sensitivity of an analog voltmeter as ohm per voltage? 🔗 https://electronics.stackexchange.com/questions/214016/why-is-analog-voltmet... <https://electronics.stackexchange.com/questions/214016/why-is-analog-voltmeter-sensitivity-is-defined-as-ohm-volt> John :-#)#
Sent from my iPhone
On Aug 2, 2026, at 12:44 PM, Tony Miklos via Jukebox-list<jukebox-list@lists.netlojix.com> wrote:
On 8/2/2026 8:42 AM, M De Simone via Jukebox-list wrote: Appreciate this response, if the hum persists we will try your recommendation. It will be a few weeks before I can get the amp back to the jukebox, out of town. Although, I’m still curious why I would read 23 vac on the chassis with my Fluke multimeter and less than 1 vac with my 1000 ohms / volt Simpson analogue meter? I’ve done this comparison before when calibrating my tube tester and the difference was minimal?
Sent from my iPhone I've looked before but not found anything on the internet explaining ohms/volt in a meter. As I was taught is that all volt meters draw a very slight current from the voltage you are measuring, putting a very slight load on the voltage. The AC you are reading isn't direct AC from the line voltage, it is from induction, so it can "provide"? only a very low current. Your Simpson puts a larger drain on the circuit and loads it down. DMM's in general have a higher ohms/volt, so it doesn't load the voltage as much. But a lower quality DMM will still have less ohms/volt than a high quality DMM. I recall one time working on a much newer, but tube Wurlitzer amp using a cheap DMM. At first the voltage across a capacitor would read a certain voltage, but it was a very touchy circuit so the load from the meter quickly lowered the voltage, drawing the capacitors voltage down.
I hope that makes any sense and I don't have too many errors.
This makes me wonder what happened to my father's tube type voltmeters?
Tony
Aug 2, 2026, at 7:40 AM, Tony Miklos via Jukebox-list<jukebox-list@lists.netlojix.com> wrote:
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox.
As for the gutted volume control, it's the way to go when installing a light weight ceramic cartridge. Some add a resistor and a cap in the pico farad range but I haven't heard a difference with or without them. I've seen them with a pot of anywhere between 10K and 100K.
Tony
On 7/29/2026 7:21 PM, M De Simone via Jukebox-list wrote: Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
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-- John's Jukes Ltd. 7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 Call (604)872-5757 (Pinballs, Jukes, Video Games) flippers.com "Old pinballers never die, they just flip out"
On 8/3/2026 3:00 AM, John Robertson via Jukebox-list wrote:
On 2026-08-02 11:12 a.m., M De Simone via Jukebox-list wrote:
Tony, Yes it does make sense. Since the recommendation is for a 1000ohms/volt I’m going with the Simpson meter results. Thanks again, Mauro
The MINIMUM is a 1,000 Ohms/Volt meter. This loads the circuit more than a modern DMM so 1000R/V will be the worst case test using the recommended resistor in the Motorola safety check.
electronics.stackexchange.com
Why is analog "voltmeter sensitivity" is defined as ohm/Volt? <#>
What is the motivation to define a sensitivity of an analog voltmeter as ohm per voltage?
🔗 https://electronics.stackexchange.com/questions/214016/why-is-analog-voltmet... <https://electronics.stackexchange.com/questions/214016/why-is-analog-voltmeter-sensitivity-is-defined-as-ohm-volt>
John :-#)#
John, I could very well have misunderstood whatever the teacher was talking about when he mentioned ohms/volt. It's no wonder I could never find it mentioned in the context I was using it in. Thinking of it now, ohms/volt doesn't really make sense for a meters sensitivity does it? I don't know where I got that from. Maybe I was having a bad day in tech school that day? If getting a little shock off equipment, I still like to test the chassis and other parts for voltage to ground with a decent meter with no resistive load on it. Tony
Sent from my iPhone
On Aug 2, 2026, at 12:44 PM, Tony Miklos via Jukebox-list<jukebox-list@lists.netlojix.com> wrote:
On 8/2/2026 8:42 AM, M De Simone via Jukebox-list wrote: Appreciate this response, if the hum persists we will try your recommendation. It will be a few weeks before I can get the amp back to the jukebox, out of town. Although, I’m still curious why I would read 23 vac on the chassis with my Fluke multimeter and less than 1 vac with my 1000 ohms / volt Simpson analogue meter? I’ve done this comparison before when calibrating my tube tester and the difference was minimal?
Sent from my iPhone I've looked before but not found anything on the internet explaining ohms/volt in a meter. As I was taught is that all volt meters draw a very slight current from the voltage you are measuring, putting a very slight load on the voltage. The AC you are reading isn't direct AC from the line voltage, it is from induction, so it can "provide"? only a very low current. Your Simpson puts a larger drain on the circuit and loads it down. DMM's in general have a higher ohms/volt, so it doesn't load the voltage as much. But a lower quality DMM will still have less ohms/volt than a high quality DMM. I recall one time working on a much newer, but tube Wurlitzer amp using a cheap DMM. At first the voltage across a capacitor would read a certain voltage, but it was a very touchy circuit so the load from the meter quickly lowered the voltage, drawing the capacitors voltage down.
I hope that makes any sense and I don't have too many errors.
This makes me wonder what happened to my father's tube type voltmeters?
Tony
Aug 2, 2026, at 7:40 AM, Tony Miklos via Jukebox-list<jukebox-list@lists.netlojix.com> wrote:
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox.
As for the gutted volume control, it's the way to go when installing a light weight ceramic cartridge. Some add a resistor and a cap in the pico farad range but I haven't heard a difference with or without them. I've seen them with a pot of anywhere between 10K and 100K.
Tony
On 7/29/2026 7:21 PM, M De Simone via Jukebox-list wrote: Here’s one for the old timers, I’m working on a model 771 amplifier from a Wurlitzer 616 and the complaint is,
“ There is significant hum primarily at 60Hz as seen in the attached spectrograms. The hum is 30dB SPL over the noise floor, is constant regardless of volume and is still there when the input is disconnected.”
I set up the amplifier on my bench and played an iPod through it with field coil and volume box from the jukebox and I get perfect sound and dead quiet with or without input.
I rebuilt the amp a few years ago but was surprised when I saw the volume box modification, it just had straight wires to volume pot and back out again. I’m only familiar with the mods for the 1940’s volume boxes. Is it different for these early amplifiers? I’m at a loss as to what might be causing this hum in his jukebox but was curious about the lack of resistor or capacitors in the volume box. Anybody familiar with these? Thanks, Mauro
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On 8/2/26 09:44, Tony Miklos via Jukebox-list wrote:
I've looked before but not found anything on the internet explaining ohms/volt in a meter. As I was taught is that all volt meters draw a very slight current from the voltage you are measuring, putting a very slight load on the voltage. The AC you are reading isn't direct AC from the line voltage, it is from induction, so it can "provide"? only a very low current.
Essentially, the ohms-per-volt specification is the loading of the meter across the device under test expressed as the resistance based on the full-scale reading of the meter. This is usually a factor with analog meters having a moving needle. Digital meters often have a high-impedance buffer where it is not a factor. If the meter is set to a full-scale reading of 250 volts and it has a 1000 ohms-per-volt spec, it will present a 250K resistance across its leads. Switch it to 10 volts full-scale and it will present a resistance of 10K ohms. Digital multimeters and old-school VTVMs typically load the input to 10 megohms or more regardless of full-scale setting. If you're measuring AC leakage to a chassis or device you're likely to see a much higher reading with a higher impedance meter. Similarly with vacuum tube circuits which tend to be high impedance. -- Jay Hennigan - jay@west.net Network Engineering - CCIE #7880 503 897-8550 - WB6RDV
On 8/2/2026 8:42 AM, M De Simone via Jukebox-list wrote:
Appreciate this response, if the hum persists we will try your recommendation. It will be a few weeks before I can get the amp back to the jukebox, out of town. Although, I’m still curious why I would read 23 vac on the chassis with my Fluke multimeter and less than 1 vac with my 1000 ohms / volt Simpson analogue meter? I’ve done this comparison before when calibrating my tube tester and the difference was minimal?
Sent from my iPhone
On Aug 2, 2026, at 7:40 AM, Tony Miklos via Jukebox-list <jukebox-list@lists.netlojix.com> wrote:
I've had a hum that was fixed by turning the tone arm 180° in it's socket. I don't recall if the plug and socket are originally polarized. Also the mains plug can make a difference by turning it, (then putting a polarized plug on it) Maybe even a ground, although some believe it is more of a danger than a non-polarized plug if you don't run a ground wire to each and every metal piece in the jukebox. Oops, I didn't mean to write "turn the tone arm", just the plug in the socket!
participants (6)
-
jay＠west.net -
JIM & LAURIE DIRKSEN -
John Robertson -
Jukebox Repairman -
M De Simone -
Tony Miklos