Hi guys,
I am attempting to build a magnatone 213 and I cannot get beyond my pt woes. I measure from what I believe to be each lead of the b+ to what I believe is the center tap and I get 230vac from each to CT. When I measure across the two b+ leads I get 7 volts or something stupid. Can anyone make any sense out of this? It is an old tranny that came out of an unknown wurlitzer organ. I am getting the 5v and 6.3 where I am supposed to and I have an extra 2 leads (one of which spits out 117ish. I have both of them put to the side and covered up because I don't think I need them for this circuit...but I'm pulling my hair out.
I am attempting to build a magnatone 213 and I cannot get beyond my pt woes. I measure from what I believe to be each lead of the b+ to what I believe is the center tap and I get 230vac from each to CT. When I measure across the two b+ leads I get 7 volts or something stupid. Can anyone make any sense out of this? It is an old tranny that came out of an unknown wurlitzer organ. I am getting the 5v and 6.3 where I am supposed to and I have an extra 2 leads (one of which spits out 117ish. I have both of them put to the side and covered up because I don't think I need them for this circuit...but I'm pulling my hair out.
OK, having desolved many a wierd XMF I can tell you that one thing is factual with no argument...if you don't have an omic representation of the expected powered up voltage readings, than you have a "ghost voltage". It's not real. I get then all the time. If your seeing 230Vac, try hooking up a small load to it to see if it can sustain a load. Like 2ea 117v light bulbs in series.
Often when hooking up an unknown PT XMF, I will always start with my ohm meter. I'll identify the 5v, 6.3v & High Voltage leads. Typically the HV windings will read about 150 to 250 ohms, and half that connected to the CT. Once you can show THAT circuit, then I spin up my variac & see for myself. Always test all the wires to all the other wires. I mean that if you think you have lets say a 5v CT, check it with every other wire, and make a diagram for your reference. Number the wires to save time if that helps.
After your measurements, what do you mean by "M", you mean Megaohm? That is basically an open circuit as comparison to a HV winding have only 200 some odd ohms.
I hope this helps...Doug
Often when hooking up an unknown PT XMF, I will always start with my ohm meter. I'll identify the 5v, 6.3v & High Voltage leads. Typically the HV windings will read about 150 to 250 ohms, and half that connected to the CT. Once you can show THAT circuit, then I spin up my variac & see for myself. Always test all the wires to all the other wires. I mean that if you think you have lets say a 5v CT, check it with every other wire, and make a diagram for your reference. Number the wires to save time if that helps.
After your measurements, what do you mean by "M", you mean Megaohm? That is basically an open circuit as comparison to a HV winding have only 200 some odd ohms.
I hope this helps...Doug
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Don't measure ohms with any voltage applied, it can break your multimeter.
You should be able to find the group of wires that have B+ with just an ohmmeter. Find all wires that ohm out, then apply power to find the voltage. Best to clip the leads to the wires. Check your ohmmeter with a known good resistor to make sure it's still good.
You should be able to find the group of wires that have B+ with just an ohmmeter. Find all wires that ohm out, then apply power to find the voltage. Best to clip the leads to the wires. Check your ohmmeter with a known good resistor to make sure it's still good.
What makes you think that these leads are HT and CT? Is because they are next to each other?
Their location is not always related to their function. I have some old trannies that have heater winding sitting next to each other, HT windings across from each other (other side of the bobbin) and the HT-ct on the other side of the core. Real confusing. Add to that an internal screen (single lead) and you are lost without an ohm-meter.
Very likely the leads you have tucked away for now are part of the HT.
Their location is not always related to their function. I have some old trannies that have heater winding sitting next to each other, HT windings across from each other (other side of the bobbin) and the HT-ct on the other side of the core. Real confusing. Add to that an internal screen (single lead) and you are lost without an ohm-meter.
Very likely the leads you have tucked away for now are part of the HT.
I missed that you were saying that you were testing for continuity (ohms measurement) with the power on, oops! I would carefully be inspecting your VOM-DVM for normal operation. A trip to your local pawn shop (if you often those places) will allow you to try one of theirs, and perhaps buy a decent replacement, Fluke brand preferred.
We have all been confused by the "ghost voltage readings". When DVMs came out many of us guys were dismayed by rare & confusing, but seemingly valid readings.
1st you should re-establish your meter, it a tech's bible as it were. Test standard stuff, like a thousand ohm resistor. Plug your probes onto a AC line & see if it still reads 125Vac or whatever your line voltage is on your bench. Once you have re-verified it's faithfulness, then you can move forward & draw your "power off" schematic representation of your XMF's internals.
Some Hammond XMFs have 2 sets of secondary HV values about 20 ohms different, all on the same winding. Other XMFs like was already mentioned have a single wire for use in bias for the screen/grid. Also a shield wire connected to the core or internal shield.
Remember, there are wire colors that can help out. Red is normally used to ID the HV winding. Always the filament (6.3) is green, and the 5.0 winding is yellow. All of these center taps are normally mixed with their respective colors with a yellow interwoven group of threads. Like the 6.3v filament will be green w/ the CT having a green & yellow wire. Same with the HV winding, the CT will be red with the yellow stripe.
That XMF will live well in your Magnatone build for sure. Great Amp. Q; Are you going to employ the industry standard FM tremolo that everyone including Fender tried to deliver buy never did & bragged that they were anyway?
-Doug
We have all been confused by the "ghost voltage readings". When DVMs came out many of us guys were dismayed by rare & confusing, but seemingly valid readings.
1st you should re-establish your meter, it a tech's bible as it were. Test standard stuff, like a thousand ohm resistor. Plug your probes onto a AC line & see if it still reads 125Vac or whatever your line voltage is on your bench. Once you have re-verified it's faithfulness, then you can move forward & draw your "power off" schematic representation of your XMF's internals.
Some Hammond XMFs have 2 sets of secondary HV values about 20 ohms different, all on the same winding. Other XMFs like was already mentioned have a single wire for use in bias for the screen/grid. Also a shield wire connected to the core or internal shield.
Remember, there are wire colors that can help out. Red is normally used to ID the HV winding. Always the filament (6.3) is green, and the 5.0 winding is yellow. All of these center taps are normally mixed with their respective colors with a yellow interwoven group of threads. Like the 6.3v filament will be green w/ the CT having a green & yellow wire. Same with the HV winding, the CT will be red with the yellow stripe.
That XMF will live well in your Magnatone build for sure. Great Amp. Q; Are you going to employ the industry standard FM tremolo that everyone including Fender tried to deliver buy never did & bragged that they were anyway?
-Doug
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