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Smoke came out of the speak selector pot on my 800c

tonyg88

tonyg88

Super Member
Hello All,

I haven't used my fisher 800c for a while but it has all the needed mods to make it last for awhile..... New power supply board,changes so that the tubes don't run as hot with biasing abilities for each tube.

I noticed that when I first turned it on I accidentally had the selector on headphones but nothing was plugged in...... I had my magnavox portable record player headphone port hooked up to the fishers aux port.

I saw some smoking come out of the speaker selector area and changed it to speaker 1 and everything was sounding great.... a few minutes later I see that one of the output tubes redplatted (They were originals too !?!!?!?!!!!) ...

So before I open it up something near speaker selector smoked up and now when I look at it from the behind the first tube on the right is redplatting after being on for 2 minutes.

What could this be?
 
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Swap the Redplating tube (which one BTW....use the Vnumber) with it's mate. I other words V-10 with V-11 and or V13 with V14). If the tube in the same socket redplates, the problem is 99.9999999&4/10 sureit's the coupling cap for that socket. If the same tube replates in a different socket, it's the tube. You will have to check the 330 ohm 1w(R1& R8) resistors at the headphone jacks (lift one end out of circuit 1st then test), and also the 25ohm 5w wirewound(R4 & R6) resistors. These two maybe at the switch or further down inside near the spkr connectors. When you check the redplating tubes makes sure you have a dummy load or a spkr hooked up to the spkr connection. Flip the unit on it's side (Power Transformer side down) and you'll be able to see where the smoke is actually issuing from.
 
Thank you I swapped the redplatted tube with one of the other output tubes. I had it on for 20 minutes so far listening to music and it is sounding great... What does that mean then?

I will test headphone jack soon to see if that still works after the smokey event and the radio..... If it is all working just fine should I even bother opening it?

I haven't used the thing for a few months and it is possible something went through the big holes on top (dust hair etc) and the high voltage fried that? but I will need to open it to be sure I know.... I tend to make things worse when I open it.....
 
Just curious, is your Magnavox portable record player a hot chassis design? A hot chassis design means that it has no power transformer.
 
cademan said:
Just curious, is your Magnavox portable record player a hot chassis design? A hot chassis design means that it has no power transformer.
Click to expand...

Oh man, GREAT question. That, if it was a hot chassis (i.e, 120VAC on the chassis) could definitely wreak complete havoc!

Regards,
Gordon.
 
You know, I only thought of that because I experienced that as a child some 40 years ago. I used to have an old Lloyds AM/FM/SW table top tube radio which I used by itself for many years. It had an earphone jack on the side of it so one day I decided to connect it to the AUX input of my dad's brand new transistorized AM/FM cassette tape deck.

I immediately smelled smoke and disconnected it and never touched it again.

The Lloyd's was a hot chassis tube radio but I had no idea at that time what that even meant. The one tube that I remember it having was a 50C5 tube.

Fortunately, my dad's radio still works today and 40 years later, you can still smell something got burned around the AUX jacks. I never ever understood why this happened. One day the 'ol Lloyd's quit working. Tubes quit lighting up so I threw it away. I had no idea at the time that only one of the tubes heaters opened up and a simple tube replacement would have brought it back to life. I would like to find another exact one someday. I would know it if I saw it!

Years later I learned why this happened. Hot chassis! No power transformer! 120VAC on one side of chassis! :yikes:
 
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I was aware of that hot chassis issue before plugging it in and I used the same record player on another tube amp and flipped the record player chord back and forth and nothing bad happened...

Even after I hooked the fisher up to my cell phone that one tube would still redplate when turned on.. The portable record player is solidstate did they make hot chassis with solid state? Here a pic of the portable amp maybe one of you can tell if it is hot or not.

See picture here (warning like 2mb) http://togerland.com/temp/pics/20170304_211442.jpg
 
I moved the portable so the polarity could have changed but the fisher has been on all night with no issues (I accidentally feel asleep with it on ) still haven't tried am/fm or the headphone jacck
 
Probably has more to do with the amplifier making signal without the speakers being switched on. I believe Fisher used a dummy load resistor in there so that something was always across the speaker terminals, and with no speaker to suck up the power all of it gets dumped into that resistor.

The red plating tube may or may not be related, though there was a recent discussion about improper loading when the headphone jack was in use that could cause a lot of stress on the screens of the tube.

A hot chassis amplifier connected to a non-hot chassis won't make smoke come out of the speaker selector switch.
 
gadget73 said:
A hot chassis amplifier connected to a non-hot chassis won't make smoke come out of the speaker selector switch.
Click to expand...

Most likely not, but it was probably something in the nearby vicinity and the speaker switch was where it seemed to come from or looked like it vented from.
 
@cademan look at this pic http://togerland.com/temp/pics/20170306_131404.jpg it looks like the power wire goes in the plastic connector and than to the motor than there are wires that come back from the motor that go into the plastic connector that travels back up to the amp.If it is using the motor to help in the voltage process could this solidstate actually be hot chassis still?

Damn looking at this pic it sorta shows how crappy it was designed all these power wires right next to the RCA cables that come from the record player cartridge...Then it uses the same path way against both of the power circuits (the one directly from the wall and then the 2nd one from the motor) No wonder why there is a slight background hum and by just touching( not changing) the control knobs it causes a louder hum until I remove my finger.
 
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Do you have a schematic? That would settle it fairly quickly. Personally I doubt its hot chassis though.

usually wiring in and out of the turntable motor and switch are part of the auto shut-down feature that turns off the amplifier when the stack of records are done.
 
@gadget73 I do not..... But is it even possible for solidstate to run like a "hot" tube amp? Has anyone seen such a design?

I have looked under the record player portion and on top where the amp portion is.... I do not see a power transformer anywhere....
 
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