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AMC Record Player has crazy loud HUMM

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ryan lambert

New Member
I have an AMC DS-10 console record player that has a crazy loud deep hum. I’ve replaced all three vacuums. The TT is grounded inside the receiver but I even went as far as to ground it once again into the outlet in the wall with a three prong plug in. The humming stops when I remove either one of the 50C5 tubes. The humming doesn’t happen until I plug in the phono power receptacle. I’ve fought with this thing for over a week now and I am pretty much an amateur and would just like some advice as to what to try or test next. I have pictures of schematics of the receiver as well as tone arm and cartridge and the electric motor that spins the TT. Desperately needing advice…
 

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Are you able to disconnect the turntable? In my (admittedly limited) eperience working on consoles the turntable should be connected manually still. I am guessing that the headshell connector is oxidised and causing issues.
 
Everything is soldered together except the phono power receptacle. But the tubes don’t activate until I plug that in and that’s when the noise starts obviously but I have yet to disconnect the cartridge itself but I plan on just disconnecting things as I go to see if I can find the issue. Not too sure on how to short things yet. But the other night I was messing around with it and tapping things with my meter while it was humming and when I touch one of the connector going from the 12ax7 tube to the volume and treble pots it makes a louder static noise so my suspicions go there but I’ll try the cartridge tonight and go from there. Thanks for the advice any more input is appreciated!
 
with no cartridge in there its going to be very prone to hum. This is an Astatic cartridge, the flipper mount thing stays in place and the cartridge with integrated needle plugs into it. Without this present its an open circuit.

Removing any tube or unplugging the turntable will shut the whole thing down. Its a series string unit so it all has to be connected for anything to work. Also being a series string unit, it has no isolation from the power line so be extremely careful in here. Its very liable to electrocute you.

if the caps have not been replaced, they're overdue and that will make it hum too.

if you have no idea what I mean by any of that, my best suggestion would be to get it to someone who does because these things can be extremely dangerous.
 
So come to find out it was my filter capacitor. It has 4 leads one of which is a common negative. I only have electrolytic capacitors to replace it but it seems that when I tie all the negatives together the capacitance goes up to 140’s. It’s like they are all in parallel and I’m unsure on how to get them all to the common negative with raising the capacitance like that. The common it’s talking about leads to the power supply. But it’s also burning up two of the 2W resistors leading to the capacitors. I can’t find anything online to help. I have replaced the 80 mfd with two 47mfd and the 40mfd with one 47mfd and replaced the 20mfd with a 22mfd with all of the voltage reading being 450v. Very unsure how to get these to not be in parallel AND connect them to the common.
 
Here is a picture of the capacitor.
 

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There are resistors across the power supply's capacitors. You need to include them in the re-capping of the unit. These form pi-filters.

Can you take & post a better photo of the schematic? Larger, too. We need this to determine what resistors are the ones that need to be included.

Thanks!
 
image2.jpg


See how R11, R13, and R14 are attached to the cap sections, of those wires coming from the cap can? Each cap section needs to be attached to those resistors, in a specific order.

The negatives can be tied to a common grounding point.
 
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I have all of the positive leads going to the positive end of the caps but like I said when I connect the negative to the common it raises the capacitance like they are in parallel.
 
ryan lambert said:
How would I go about doing that? R13 and R14 were the ones that were failing when I plugged it in.
Click to expand...

Okay. What you should have done is remove the old lines from the cap can, one-by-one. Replace with stand-alone proper value axial caps, one-by-one. I assume that you have completely removed the can without noting what section of that can goes where? :idea:

You will prolly need new R13 and R14 resistors. Buy same value metal oxide, 2-watt rated ones. Get individual 20mfd/450 or 500VDC, 80mfd/450 or 500VDC, and 40mfd/450 or 500VDC electrolytic caps.

Once you have the stock, prolly best to go step-by-step, in the replacement process.

:)
 
ryan lambert said:
I have all of the positive leads going to the positive end of the caps but like I said when I connect the negative to the common it raises the capacitance like they are in parallel.
Click to expand...

They are NOT in parallel! That the problem. They are in adjacent pi-filters separated by specific resistors.
 
It was one of those wax capacitors but it was labeled with what lead goes where. I already replaced those resistors. Would it hurt putting new modern value capacitors instead of the axial caps?
 
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