Vintage stereo help

I have a 1962 RCA Victor portable record player,  model 4VC82. This thing is near mint. About a year ago, one speaker would fade in and out. Stomping on the floor would bring it back. It isn't a full drop out, just muffled, like someone is twisting the volume knob up snd down. That to me spells loose wire or component. 

I open up the speakers and unit. I tighten up the spade connectors. No change. I switched the wires. The fading seems to follow the switch. I checked to see if the fading followed the wires, but it didn't. 

What part of a solid state stereo would let the sound drop out like that? Could a failing fader do that? Bad resistor?  Bad tube?

I'll add pics when I get home. 

I'd start by dousing all the switches and rheostats with a good dose of electronics cleaner and go from there.  

Tubes seem to last a pretty long time.  Have you noticed that one of the tubes is losing or has lost most of the silver stuff on the top or sides of it?  That seems to be "consumed" and eventually the tube dies when it's gone.  

I'd pull out and re-seat all the tubes, too, while I'm at it.  

Yeah, I'd be looking at anything like a potentiometer that could (would!) be oxidized.

Awesome. Will start there. Thanks for the vectors.

It looks like that unit has toobz:

Could be one of the output tubes, V2 or V3.

***Danger Will Robinson, this test can expose very high voltages***  If you are comfortable doing so you can do a "chopstick" test.  Open the cover to get access to the tubes, power the unit up, play a record, and using a wooden "chopstick" gently tap on each of the tubes.  If you hear the output change whilst tapping you have your culprit.

In the meantime I can dig through my toob stash to see if I have replacements.

Woah! single ended 50c5 stereo outputs.  These are table radio tubes. It might be pushing 1.5 watts per channel! 

You will have a lot of capacitors at the end of their lifespan in something that old. That is where I would start. Wax paper caps, old electrolytics. Then a ton of carbon comp resistors that have drifted in value over the years. They tend to drift up in resistance over time.

Also that is a transformerless circuit

EDIT: What I mean by this is there is NO ISOLATION between the wall outlet and the chassis.  It is quite possible that you can shock the bejeezus out of yourself by touching anything in it while it is plugged in even with it switched off. It has a non polarized two prong cord so if it is in the wall socket upside down your chassis will have 120V AC on it. Add in the fact that the filter capacitors in the power supply can store several hundred volts DC even after the unit is powered off for days and you can see why the warnings are needed.

That is a transformerless circuit and the chassis will potentially be hot, especially with leaky caps allowing voltage to ground. Be careful. Two fifty volt heaters plus the 12V heater from the single 12AX7 equals 112 volts. With modern wall voltage around 120 that means you will have an extra ~8 volts looking for trouble and will need to up the resistor value in the heater circuit to soak that up. The schematic is fuzzy and hard to read I can't see the current value.

Sweet. Yup, three tubes. There's a hatch at the back. The warning is awesome. RCA had more faith in people back I  the 60s. 

The file downloaded as a .pdf, I tried to convert it into a .jpg.  It was free from radiomuseum.org.

Maybe these are more legible?

Based on the power supply retaining power for possibly days later, how long should I wait to try te-seating the tubes?

Also, tapping on the center tube, changesthe outut. Weather it's the tube, or a loose component bear that tube is unknown.

DO NOT DEFEAT ITS PURPOSE. Ha!

best cover ever

In reply to Appleseed :

Cool stereo guts. Check in and let us know that you have not been electrocuted yet. 

Unplug it, let it cool.  You can touch the tubes without killing yourself.  When in doubt, put one hand in your back pocket and use the other one.  If you're really paranoid, then take a plastic handle screwdriver, put an alligator clip lead on it and ground the other end of the clip lead to the chassis.  Then (remember, this is unplugged), touch the leads on that big pink thing sticking up in the air, which near as I can tell is R20, and the circuit board side of that diode that is the metallic can with the diode drawing on it right next to it the big pink thing in your pic.  That should ground out anything left over.

Man, I still have a 4CX1500b around here somewhere.  Maybe a 3CX1500 too.  And a 4KV at an amp plate transformer. All I need is a socket for one or the other and a cathode transformer.  You wanna talk toobe power....

Tough call on this one from here.

If it were my rig here at home, I would leave it unplugged for a good three or four days and change the suspect tube.  I would do so knowing that by removing the old tube and pushing in a new one, if there was a loose connection on the tube socket I may have just turned the thing into a project instead of a mostly working player.

But I'll let others more knowledgable than me weigh in on that one.

**Edit** I didn't get a chance to dig through toobz here to see if I have a replacement for you.  If you decide you want to try one I'll see what I have and send you one if I do.

The tubes will be safe to touch.  The big silver can is your filter capacitors.  The wires or traces leading to it are the baddies. If tapping one tube brings it back I would suspect corrosion on the pins or socket. Contact cleaner and cycling it in and out of the socket should clear it up

Tube nerd here, short version:

Bad tubes happen, but are generally more rare than other failures. Any glass tube, with silver shiny stuff still silver (turns white if seal breaks), is usually not suspect unless proven. Tubes only 'wear' when used. Old tubes are nearly always better than modern reproductions, so don't replace willy nilly. Any glass tube is safe to touch while on, but be safe and use a wooden chopstick to tap on stuff to see whats loose. Be aware, many tubes are naturally a bit microphonic, but shouldnt be a huge sound. 

Usually the culprit is the electrolytic capacitors, that have a working life of about 25 years, but also age when unused unlike tubes and resistors.

If a cap went out it can often fry a resistor as well. Tubes seldom go bad unless abused or very high lifetimes. If you are handy with an iron, replace EVERY electrolytic capacitor (all wax ones too!). Test anything that looks odd and replace if too far from spec. 

Even in fully restored condition, this thing is dangerous. The only real solution is an isolation transformer, or being an adult, and accepting the risks. PAY attention to the polarity of the plug, if not polarized, there is a 1 in 2 chance, EVERYTHING metal is at wall voltage, hence the alarming cover. 

I use these old radios plenty, but unplugged when not in use, and hidden from curious children. Not unlike a dangerous powertool. Transformer design tube equipment has its own dangers, but they are not inherent to the casual user like the transformerless units. Many a clueless guitar player has tried to convert one and paid the ultimate price.

Any chance, someone could lable the pics I took with what they are? I am handy with a soldering iron, but I cannot, for the life of me, easily read wiring diagrams. It would be a massive help. Also, the plug is extremely loose. I'd like to believe that the female part of the connection, the part in the plug itself, is egged out thus not having a good "grip" on the male component. Any idea where to get a replacement. I'll snap a pic soon, but it plugs into the receptacle that's right below the pink component in the third picture I posted. Best I can tell, the plug is non-polarized!

They are all labeled on the circuit board drawing you posted.  The big can on the right is C5.

The part about not being able to read a wiring diagram means I can't read the wiring diagram. Tell me that it's a .0025ohm resistor, bam easy, but to look at the diagram an be able to deduce that it's a .0025ihm resistor, nope. I have no knowledge of reading these things.

To navigate these things and decode them, I usually look for a component that doesn't blend in with the rest of them and use that as a landmark to navigate everything else.  For example this single potentiometer circled in blue versus the others which are doubles:

Being a type of resistor it will be labeled with an "R", and on the drawing of the circuit board it should be right in line with the others.  Like this:

So the circuit board sketch shows you where that potentiometer is -physically- on the board, and it's name is R15.

Knowing the name of the component, you can scan the schematic to see what the thing is and where it is -electrically-.

Looking for R15 shows up in this blue circle:

Based on the schematic that pot serves as your balance control, and is 1 Megohm in value.  In fact I bet it's stamped 1M on the back.

So what I do now that I have a starting point is get the physical board and the drawing for the board in the same orientation in front of me, and you can walk through all the rest of the components in this fashion.

Capacitors (marked with C's) give me a headache still.  The reference I use to keep them all straight is here.

If you plan to go through the board and replace components as they are you don't really need to know what they are doing in the circuit.  Just desolder the old and solder in new one one at a time.

I hope this makes sense...

**Edit:  Your tubes on the schematic (not the circuit board drawing) are in black circles and are labeled with V's (valves) and then the valve type.  The tricky part is V1A and V1B are in the same physical glass tube, and are type 12AX7A.  This is confusing because the schematic seems to show four tubes, but your player only has three.  The other two, V2 and V3, are 50C5's and I'm almost certain I have some in the basement.  If not that exact type, I likely have the equivalent.  They are yours if you want them.

I see. The circuit board diagram is looking up from underneath the board. I couldn't figure out why the single pot potentiometer was on the left side in my picture, but on the right side in the drawing. Thanks. Use the circuit drawing to find the name of the components on the wiring diagram.

Where's a good, cheap place to buy replacement resistors and capacitors? 

That's it, you got it.  I didn't catch it last night, but your big can capacitor C5 has two "sides" as well, C5A and C5B.  As for the power cord, my first thought was to find an IEC style polarized replacement cord and socket, but I'm not sure what's available.

Personally I've dealt with Amplified Parts/Antique Electronic Supply (same place, two websites) the most and they are very good.  That was in the context of a guitar amp though, I'm not sure if they will have all the caps you need for the player.  Parts Express has been good for some stuff too.  I have heard great things about Tube Depot as well but I haven't dealt with them.

I found a couple toobz for you if you need them.  I also have many 12Axx types if you need a couple of those.  And tube sockets too...

Awesome. Thanks. Honestly I think the tubes are ok. It's probably the caps and resistors.