Voice of Music Tri-o-matic Model 560A Issues

[Captainclock]

Originally Posted by dieseljeep

Go to an auto supply store and get a can of brake cleaner. Be careful and use it in a well ventilated area, as it's some nasty stuff. Also, be careful around plastics, as it will cloud or discolor them.
Checking voltages, you have to have the amplifier powered on. If you want to be sure that there wont be further damage to other components, remove the rectifier tube, probably a 5Y3.

Yes the Rectifier is a 5Y3GT tube, but anyways I measured the voltage on the heaters for the 12AX7 tube and it measures at around 104 volts which I'm assuming is what its supposed to measure (I don't have a service manual for this unit so I don't know what the voltage is supposed to be exactly) and all of the other tubes glow like they're supposed to its just the 12AX7 that doesn't glow for some reason or another (unless the shorted 5Y3 that was in this thing originally took out the 12 Volt winding in the power transformer...)

[rca2000]

If you are seeing 104 volts on the fimamant pins...it is some sort of bias applied to the line. That is NOT the filamant voltage...it should be either 6.3 or 12.6 volts AC_-NOT DC..ACROSS the filamant....NOT to ground.

I had to help someone working on a commercial clothes drier today...the heater would not come on. he had measured 120 volts AC--to GROUND on EACH heater pin...but he did NOT realize...you have to measure ACROSS BOTH PINS..to get the right reading of the supply to the element !! He had chenged nearly EVERYTHING...the element..thermostats, limits, even motor and centrifiigual switch....STILL no heat. It took me maybe SEVEN minutes...to find an open switch on the timer. Measuring ACROSS the element reveeled NO voltage... and when the timer switch was bypssed FULL heat began to work fine !! he just said "I have trouble reading diagrams" and i let him know...I have known how to read diagrams since about TEN years old !! This guy has worke don this stuff since I was a CHILD...not really SURE HOW one can effectively repair things like this... WITHOUT knowing how to read a SIMPLE diagram...for a MECHANICALLY controlled clothes drier?

SO..my point is measure ACROSS BOTH pins --to see if you are getting filament voltage...and likely it will be AC. It iS possible that it is a seperate DC supply....but nOT likely on that cute little amp. I have a couple of those nicely-built players myself. One was a goodwill purchase for a long time ago...the other I think I got at an auction for nearly nothing some years back...

[Captainclock]

Originally Posted by rca2000

If you are seeing 104 volts on the fimamant pins...it is some sort of bias applied to the line. That is NOT the filamant voltage...it should be either 6.3 or 12.6 volts AC_-NOT DC..ACROSS the filamant....NOT to ground.

I had to help someone working on a commercial clothes drier today...the heater would not come on. he had measured 120 volts AC--to GROUND on EACH heater pin...but he did NOT realize...you have to measure ACROSS BOTH PINS..to get the right reading of the supply to the element !! He had chenged nearly EVERYTHING...the element..thermostats, limits, even motor and centrifiigual switch....STILL no heat. It took me maybe SEVEN minutes...to find an open switch on the timer. Measuring ACROSS the element reveeled NO voltage... and when the timer switch was bypssed FULL heat began to work fine !! he just said "I have trouble reading diagrams" and i let him know...I have known how to read diagrams since about TEN years old !! This guy has worke don this stuff since I was a CHILD...not really SURE HOW one can effectively repair things like this... WITHOUT knowing how to read a SIMPLE diagram...for a MECHANICALLY controlled clothes drier?

SO..my point is measure ACROSS BOTH pins --to see if you are getting filament voltage...and likely it will be AC. It iS possible that it is a seperate DC supply....but nOT likely on that cute little amp. I have a couple of those nicely-built players myself. One was a goodwill purchase for a long time ago...the other I think I got at an auction for nearly nothing some years back...

Well they have both heater pins (pins 4 & 5) tied together (the terminals are bent together and soldered together with the heather wire soldered to that point) and then pin 9 (which apparently is a heater pin as well) is connected to ground so I didn't bother measuring that one. So I take it that I need to measure between both pins 4 & 5 and pin 9 to get the heater voltage reading?

Well measured across pins 4 & 5 and pin number 9, and I only got a little over 6 Volts AC instead of 12 Volts AC, So what does that indicate?

[rca2000]

Well...if you are getting about 6 volts AC between the pair of tied pins and the other one-- pin 9 ...BUT the tube STILL will not light..and you are SURE this tube is good (likely it IS)..I would DEFINITELY say you have socket issues !!

[Captainclock]

Originally Posted by rca2000

Well...if you are getting about 6 volts AC between the pair of tied pins and the other one-- pin 9 ...BUT the tube STILL will not light..and you are SURE this tube is good (likely it IS)..I would DEFINITELY say you have socket issues !!

well it would make sense like I said the tube socket itself appears to have a bad case of Cadmium Corrosion and I don't know how that would affect the tube socket itself and its ability to allow it to make contact between the socket and the tube. and yes the tube is a known good tube, in fact its a NOS Tung-Sol 12AX7 tube that I had found in an old tube caddy someone gave me that was full of NOS tubes of various brands.

And how could a 12 volt tube still work even with only 6 Volts on the heater pins? wouldn't that cause the tube not to glow or barely glow?

[rca2000]

The 12AX7 tube is one of those that have a dual-filamant-- tied together-- with a tap in the center. If one ties the other pins at one end and then puts the other potential at the tap--you CAN use it on 6.3 volts--as is done a LOT. That is why those 2 pins are tied.

[Captainclock]

Originally Posted by rca2000

The 12AX7 tube is one of those that have a dual-filamant-- tied together-- with a tap in the center. If one ties the other pins at one end and then puts the other potential at the tap--you CAN use it on 6.3 volts--as is done a LOT. That is why those 2 pins are tied.

Ok, so then how would I fix the socket issue? I don't have any extra sockets laying around to replace it with, and I also don't have any way to clean the cadmium corrosion off of the socket which I have a feeling that the cadmium corrosion has something to do with why the tube isn't working.