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Hi all,
I obtained a Conn strobotuner ST-2 from the mid 1950's in non-working condition. It is an interesting piece of equipment with a microphone primarily for tuning a piano. It apparently can accurately tune each note in 7 different octaves. As was reported to me the strobe tuner was accidentally left plugged in and powered on for an unknown period of time. Carefully and safely, I have plugged the device in using the 2 prong power cord. I checked the chassis voltage with respect to the household ground at the wall outlet.
Here is what I found on the chassis:
Power switch off:
91 volts ac with 2 prong plug in orientation A
3 volts ac with 2 prong plug reversed to orientation B
Power switch on:
210 volts ac orientation A
125 volts ac orientation B
This can't be good. Luckily I know how to safely work around this but I will not use it or be comfortable working with it until I understand what the problem might be.
I did see that all of the tubes were glowing except for one. This tube was a 6X4 rectifier tube. I have a new one ordered but will not install until I understand what is happening with the hot chassis.
Now for the help that I need. I understand how to be safe with working on electronics. I know how to discharge capacitors. I know how to use a multimeter. I fairly well understand how current flows through a circuit. I even know the basic function of many of the components of a circuit. This might be near the limit to my understanding however. That said, I don't understand what might be causing the hot chassis or how to isolate the problem. I also don't know how to identify the reason for the 6x4 tube not powering up (I assume this is the likely reason the unit doesn't work).
I could easily take this to a technician to fix it but I would learn nothing except how to spend $100 on something that is worth $100. I want to learn! I only know one person that has any experience with vacuum tube electronics. This is an nice older gentleman that goes to church with me. Nearly every Sunday for the past 2 years he has introduced himself to me as "Bob with one O" and asked me my name. I love the old guy but I think he is 90.
Trying to learn, I understand that that a leaky cap may be the culprit. Am I correct? Should I proceed with a re-cap job?
I don't think a bad rectifier tube would cause this. Am I correct?
I feel that I should install a 3 prong/3 wire power cord for safety. Would you agree? Should it be wired as follows?
Ground (green) to chassis
Hot (black) to power switch
Neutral (white) to the transformer
Do I understand correctly that this wiring orientation is to ensure that there is no interruption by the switch from discharging the circuit when the power switch is off?
I will attach a circuit schematic for this model that also has a parts list.
Please help me learn. I want to know. I will throw this strobe tuner in the trash before I take it to someone to fix it for me. I wanted it only to learn. I don't really need it. It is overkill for tuning my guitar.
Sorry for the long post
Thank you!
Stephen
I obtained a Conn strobotuner ST-2 from the mid 1950's in non-working condition. It is an interesting piece of equipment with a microphone primarily for tuning a piano. It apparently can accurately tune each note in 7 different octaves. As was reported to me the strobe tuner was accidentally left plugged in and powered on for an unknown period of time. Carefully and safely, I have plugged the device in using the 2 prong power cord. I checked the chassis voltage with respect to the household ground at the wall outlet.
Here is what I found on the chassis:
Power switch off:
91 volts ac with 2 prong plug in orientation A
3 volts ac with 2 prong plug reversed to orientation B
Power switch on:
210 volts ac orientation A
125 volts ac orientation B
This can't be good. Luckily I know how to safely work around this but I will not use it or be comfortable working with it until I understand what the problem might be.
I did see that all of the tubes were glowing except for one. This tube was a 6X4 rectifier tube. I have a new one ordered but will not install until I understand what is happening with the hot chassis.
Now for the help that I need. I understand how to be safe with working on electronics. I know how to discharge capacitors. I know how to use a multimeter. I fairly well understand how current flows through a circuit. I even know the basic function of many of the components of a circuit. This might be near the limit to my understanding however. That said, I don't understand what might be causing the hot chassis or how to isolate the problem. I also don't know how to identify the reason for the 6x4 tube not powering up (I assume this is the likely reason the unit doesn't work).
I could easily take this to a technician to fix it but I would learn nothing except how to spend $100 on something that is worth $100. I want to learn! I only know one person that has any experience with vacuum tube electronics. This is an nice older gentleman that goes to church with me. Nearly every Sunday for the past 2 years he has introduced himself to me as "Bob with one O" and asked me my name. I love the old guy but I think he is 90.
Trying to learn, I understand that that a leaky cap may be the culprit. Am I correct? Should I proceed with a re-cap job?
I don't think a bad rectifier tube would cause this. Am I correct?
I feel that I should install a 3 prong/3 wire power cord for safety. Would you agree? Should it be wired as follows?
Ground (green) to chassis
Hot (black) to power switch
Neutral (white) to the transformer
Do I understand correctly that this wiring orientation is to ensure that there is no interruption by the switch from discharging the circuit when the power switch is off?
I will attach a circuit schematic for this model that also has a parts list.
Please help me learn. I want to know. I will throw this strobe tuner in the trash before I take it to someone to fix it for me. I wanted it only to learn. I don't really need it. It is overkill for tuning my guitar.
Sorry for the long post
Thank you!
Stephen
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