Help Identifying Transformer
- Thread starter Paul Farria
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cademan
Lunatic Member
Hi, are you sure the transformer is bad? These things are pretty much bullet proof so I was just wondering what led you to believe that it is bad?
This is a series string hot chassis so be careful when working on it. Chassis can have 120 volts on it depending on which way the cord is inserted into the wall.
If you have no sound, I would first suspect the 35W4 rectifier tube, then check the 4.7K ohm resistor.
This is a series string hot chassis so be careful when working on it. Chassis can have 120 volts on it depending on which way the cord is inserted into the wall.
If you have no sound, I would first suspect the 35W4 rectifier tube, then check the 4.7K ohm resistor.
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Paul Farria
KrypticBytez
I have 2 sets of tubes so I can rule that out. I also tested all the voltage points on the schematic along with the resistors. All of the capacitors are new. I have 120v going to the transformer but I get nothing on the output. This was a weird transformer how they have it wired so that's why I was asking for information for a replacement. Oh and all pots and tube connections have had deoxit.
The fact that the transformer has B+ voltage across it is not proof that there is sound being modulated onto that B+ by the 50C5 output tube. With one hand in your pocket, touch the grid of the 12AV6 (Pin #1) with a meter probe (don't have the other meter probe connected to anything), with the volume control set to full volume, and see if you get a buzzing sound from the speaker. If you DO get the buzzing sound, your transformer is fine and your no sound problem lies elsewhere (like perhaps the cartridge, the #1 no sound failure of old record players) .......
Paul Farria
KrypticBytez
Awesome information, I'll test that out tomorrow.
cademan
Lunatic Member
If you know anything about how transformers work, there should never be any continuity between the primary and secondary windings.
The secondary windings on your transformer show 4 wires where two are the 1.8 ohm speaker output and two are the feedback windings. Perfectly normal for this type of design.
When testing for any open windings, you use the ohms settings on your meter and test the speaker and the feedback windings for continuity.
I suspect that you are pretty much a novice on this sort of thing so I suggest you learn to use your meter on how to take both voltage and ohms measurements.
Aside from an open resistor or other bad part, Init4fun has the right idea for testing for sound and yes, it could also be a bad cartridge.
The secondary windings on your transformer show 4 wires where two are the 1.8 ohm speaker output and two are the feedback windings. Perfectly normal for this type of design.
When testing for any open windings, you use the ohms settings on your meter and test the speaker and the feedback windings for continuity.
I suspect that you are pretty much a novice on this sort of thing so I suggest you learn to use your meter on how to take both voltage and ohms measurements.
Aside from an open resistor or other bad part, Init4fun has the right idea for testing for sound and yes, it could also be a bad cartridge.
If that transformer is defective (but it's probably not), you'll need to use a generic replacement such as one of those made by Hammond, then add a feedback loop to the circuit. The chance of finding a replacement transformer with a feedback winding like this one almost zero.
Jack
Jack
Paul Farria
KrypticBytez
Well I checked all the resistors they are in spec, I replaced all the caps, solder joints look nice, and I tried 3 different 35w4 tubes no audio output. So I got a universal output transformer wired it up but only issue I have is the feedback loop. I have the two wires still soldered to the main board but of course this transformer doesn't have a place for them and I can't tell by the schematic what voltage the yellow wire should have. Swapping out output transformers isn't anything hard for me its just this feedback loop i'm new at. So what do I do with the yellow and brown feedback loop wires? I also tested the origional output transformer like requested by touching pin 1 of the tube but sadly still no audio (crackle or anything).
The brown wire is essentially ground, zero volts. The yellow wire is negative feedback, and in this case it has both a DC blocking cap (so the transformer winding doesn't pull the cathode of the12AV6 to ground) and a resistor for controlling the amount of feedback. With the yellow wire disconnected, gain should go up. If you have no output, something else is wrong.
Jack
Jack
Paul Farria
KrypticBytez
Yeah something is going wonky thats for sure. I tried new tubes and even thought maybe the speaker was bad so I hooked up a new one of those, plus I'm using the new output transformer so that can be ruled out. Talk about a head scratcher. Guess I'll go back to testing the components again, its just a very simple board there isn't much to actually test the only thing it could be now is something with the caps I changed.
Paul Farria
KrypticBytez
Ok so I tested out of curiosity pin 7 on the rectifier and its supposed to have around 120v but I'm getting 0 so I guess this means the rectifier is blown. I know when I first done all this I had a cap installed backwards by mistake and I saw the rectifier glow very bright guess it died. I'll buy another one, joy joy. I really hate tubes at times haha.
cademan
Lunatic Member
Test the old output transformer for continuity on the secondary with your meter set on ohms. If there is continuity, it is fine and you should be using the old transformer because it has the feedback loop.
This one is really easy and yes, if a cap was installed backwards, it can take out the rectifier tube.
This one is really easy and yes, if a cap was installed backwards, it can take out the rectifier tube.
