Phonoland

Hello Phonoland group! I have a 1962 Voice of Music model 357 record player with amp. I am getting a little bit of humming coming from the volume control when you turn up the volume. The louder you turn up the volume, the more notice of humming. The filters in the amp seems to be good, but just the humming from volume control only. This amp uses 2 - 50L6 GT tubes and 1 - 12AX7. It's not the best of amp either.The cartridge from the tonearm is fine also. The V-M record changer is grounded. How can I get this annoying hum to stop?? Thanks for your help

Amplifier needs to be re-capped. Eventually this problem will take out a tube or two with it. Lots of smoke usually accompanies this event. If you don't know how to restore an amplifier and you do not desire to learn on the job, I suggest a service tech.

---and just in case someone does not realize it---
Once the smoke is released, from ANYTHING electronic, there is about a 99 and 44 one hundredths % chance that it will not function--and also a good chance a fire will result !
Ron Rich

Asides from the usual capacitor reeplacement, I'd suspect a poor ground in the input signal leads and corrosion of the connections.
That white powdery dust you see is cadnium plating gone south, and not good to breathe.

2013 - 1962 = 51 years = well due for restoration.

Poor ground from the input signal?? I don't have the schematics for this unit. Where do I start to look for the bad ground in the input signal? Thanks!!

tmp58 wrote:Poor ground from the input signal?? I don't have the schematics for this unit. Where do I start to look for the bad ground in the input signal? Thanks!!

If you think you need schematics for something like input connector corrosion and such, I'd recommend you locate a reputable service tech locally to go over the unit.

Matt, I appreciate the replies. I am capable of some restoration on tube electonics. However, this 357 amp has a bad ground somewhere. When A/C line plug is reversed, the humming is worse.The filters all checked ok as far as B+ is concerned. The volume control is the one that is picking up the hum whether it's turned up or down. The louder the volume control gets turned up, the louder the hum. It doen't matter what VM record chnger I can use on this. Any more help would greatly be appreciated before I really tear in the amp. Thanks!

tmp58 wrote:Matt, I appreciate the replies. I am capable of some restoration on tube electonics. However, this 357 amp has a bad ground somewhere. When A/C line plug is reversed, the humming is worse.The filters all checked ok as far as B+ is concerned. The volume control is the one that is picking up the hum whether it's turned up or down. The louder the volume control gets turned up, the louder the hum. It doen't matter what VM record chnger I can use on this. Any more help would greatly be appreciated before I really tear in the amp. Thanks!

Variable hum level means trouble with grounding, and/or weak filters, and/or tube issues and/or ground loops, etc..... the list could go on till the cows come home. I can't diagnose such things over the internet accurately. - it's got to be on my bench at the shop.
People think us tech-pros can give an answer and a "fix" over the computer screen, but when dealing with vintage equipment it's really impossible.

Regardless, an amp this old needs recapped. If you know how to replace capacitors (e-caps & any paper ones) then I suggest you begin there. You can leave the mica ones alone for now. Test the tubes, clean all corrosion you find. Now at least if you continue to have hum you can begin to trace it without these old components complicating the process.

BTW: Pictures would be of great assistance.

Problem found......The VM 357 amp is already grounded in the chassis amp. The almost correct record changer was grounded from motor to metal base of changer. All was needed was to disconnect that wire. Variable humming stopped.

Aha! A ground loop. Too many grounds are just as bad as no ground.

If a ground for a low level source provides a loop of wire and/or chassis metal, a magnetic field causes a rather large AC current to circulate in the loop (very low resistance). This can cause the ground connection at either the pickup or the amp to have a signal impressed on it. Thus, the amplifier gets both the signal and the hum.

Ground loops are sneaky, because you can do something that seems unrelated to the parts that have the symptom that causes it. Often the ground loop is completed by three-prong power plugs. DO NOT defeat the safety ground to remove a ground loop. Other remedies are available.

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This reminds me of the strangest hum problem I ever repaired. The guy had a rather expensive stereo. One day, there was a hum in the right speaker just after he added a new tape recorder. We spent three hours checking connections on the recorder. In particular, we checked for ground loops. No luck.

The volume control didn't change the hum level. Removing the recorder connections didn't change the hum level. And if it had been power supply filters (on a nearly new receiver), it should have affected both channels.

Finally, I turned off the stereo to check the speaker connections, again looking for an accidental ground loop. The hum was still there with the power off!

A family member had hung a new electric clock on the other side of the wall behind the right speaker. The hum was mechanical vibration coming through the wall. The repair was rubber feet on the back of the clock.

tmp58 wrote:Problem found......The VM 357 amp is already grounded in the chassis amp. The almost correct record changer was grounded from motor to metal base of changer. All was needed was to disconnect that wire. Variable humming stopped.

Now, see?
I'd have no possible way of knowing that a "replacement" record changer was installed in that unit, and wired differently, causing the ground loop (which I did mention previously) problem.
This changer-swap was not mentioned in any post but this one, and "online" troubelshooting would continue as I stated "until the cows come home".

That said, I stand by my earlier comments, the internet cannot replace having the unit on a tech's bench for troubleshooting. - there's always a possibility of some "variable" being in the mix to confuse and confound things.

In most magnetic cart. systems, the "ground" is isolated at all points except at the amp. The "shield wire" is used as a ground return for the cart. only, and technically called a "drain".
In most jukeboxes, "hummmmmm" can be caused by either a "latch bar solenoid" ( if so equipped), or many times by the fluorescent lamp ballast. This can be the result of the rubber stand-offs becoming "hard", or some "repair person" replacing the ballast, but not the stand-offs. CAUTION: Never attach a ballast to wood, without using stand-offs--fire WILL result !
Ron Rich