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?
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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
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