Old Symphonic 16-S Record Player Problems

[corgan4321]

I've got this old Symphonic 16-S Record player that functions but has a problem. When I turn it on, it's fine, but once the power tube warms up and passes voltage, the speaker emits a constant noise. The noise doesn't get louder/softer by turning the volume knob, it only goes away when I power the unit off. It sort of sounds like an open circuit but the machine fully functions: when I touch the needle (CAREFULLY), I can hear it coming out of the speaker, just quietly in comparison to the very loud humming noise.

I cleaned the power tubes socket with contact cleaner and heated up each solder point for good measure.

My suspects are the two caps and the tube. I don't feel like it is the tube though just because these are pretty reliable tubes in general. The caps are more likely culprits... Which one is that blue rectangular cap though?

Also, why is the selenium rectifier only connected on one side? The positive side's lug is cut off and nothing is connected to it.

I tried following the schematics but it seems the designs changed quite a bit during production as the schematic doesn't match up with the circuit.

Any help would be greatly appreciated! Thanks. just trying to get this to work to play records...

[52 Bill]

...very loud humming noise.
My suspects are the two caps and the tube. I don't feel like it is the tube though just because these are pretty reliable tubes in general. The caps are more likely culprits... Which one is that blue rectangular cap though?

Yes, from your description you have bad filter caps. The filter cap you need to replace is the big aluminum can next to the tube. You either replace the dual unit can or wire in two separate individual caps.

Also, why is the selenium rectifier only connected on one side? The positive side's lug is cut off and nothing is connected to it.

Someone has already replaced it with a solid state diode. Rather than remove it they left it there as a tie point.

[corgan4321]

Great, thanks for the response!!!

Solid state diode? Where is it? I don't see it! hah

I guess finding two separate caps for the two values would probably easier, I'll get on that.

I thought someone had since gone in there and changed a few parts...

Again, Thanks for the response!!

[52 Bill]

Solid state diode? Where is it? I don't see it! hah

It's the blue rectangular box attached to the 130 ohm resistor.

Edit:
Oh yeah, remember that this is a line powered amp that is directly connected to the AC line.

Use extreme caution when working on this thing.

[tim]

It's the blue rectangular box attached to the 130 ohm resistor.

Edit:
Oh yeah, remember that this is a line powered amp that is directly connected to the AC line.

Use extreme caution when working on this thing.

I was thinking the EXACT same thing on the "being careful". If you have one, use it with an 1:1 isolation transformer to be safe.

[corgan4321]

What do you mean about it being inline? Do you mean that there is no transformer that steps down the voltage?

What dangers does this present besides the obvious fact that the current is higher in the circuit?

It's not like I'll be working on the amp while it's plugged in and I discharge the caps each time I turn it on and then off.

Ahah, that blue box didn't look like any cap I've ever seen, that's why.

[corgan4321]

Also, I can't seem to find any info on a 1:1 Xformer like where to get them, who makes them and such. Thanks again

[icefloe01]

It's the blue rectangular box attached to the 130 ohm resistor.

That little blue block looks kinda like a trimpot with only the wiper and one side connected. There's an unconnected pin at the bottom of it. I guess it's possible it's a dual diode package and only one diode is being used in there...

Eric.

P.S. I wouldn't let whoever worked on it before touch it again. Not very good workmanship in there...

[52 Bill]

Line powered means no transformer and therefore no isolation from the ac wall outlet. If you look at the schematic the ac line goes directly to the switch and then to the rectifier. If the line cord is not polarized or the outlet is wired incorrectly, the ac hot could be connected to what you would consider the ground circuit.

The metal chassis should be isolated from the circuit ground by the 0.05 uF cap, but you still need to use caution when working on this amp. In fact you may want to replace that cap just as a safety precaution with a new class X cap and if it isn't already polarized change out the ac cord.

A 1:1 or "isolation" transformer would separate the circuit from being directly wired to the ac wall outlet.

[baddog]

I bought two 12v x 120v transformers from radio shack and wired the 12v sides together then used one of the 120v side of the transformers for power to the amplifier and the other side is conected to the line voltage coming from the wall outlet. THis created isolation from the 120v coming from the wall socket. But this will only work if you have room to install the transformers.

Baddog