Old New Sensor Bassman OT wiring

[edge59]

Hi, I have a old what looks like a older New Sensor Bassman style output tranny with Black (common?) yellow, green and orange secondary taps, can anybody tell me what ohms taps are what? I know about the primary side, is there a way to read with a meter? It is the solver end bells, almost looks like a Twin OT.

Thanks
Ed

[The Dude]

Any numbers on it? Aside from taps, it may be helpful to know the input Z. You can ohm out the taps to get the order (the taps farthest apart will obviously have the most resistance).

[Justin Thomas]

Hi Ed,

Got your PM. Which Bassman, the 50W or 100? I have a New Sensor Bassman OT 238-9608 (Thordarsen?) w. only a 4ohm tap and I have a Schumacher 125A29A/022889 w. 606-1-10 (4x6L6, 4ohm) OT. Both have only Blue/Red/Brown pri & Green/Black sec. No other taps. None of the trannies currently installed in my amps have any other taps.

I think if your meter is accurate & sensitive enough, you might be able to ohm out the taps. But it'll possibly be fractions of an ohm. Best might be to contact the mfr. Sorry I couldn't help more!

Justin

[The Dude]

Calculating output transformer impedance | Tube Amps & DIY

This may help.

[edge59]

Calculating output transformer impedance | Tube Amps & DIY

This may help.

Thanks guys I will look that info over, I dont see any numbers at all on the transformer, just the colored wired I mentioned. I did get incremental ohm reading on the secondary like 1.9, 1.8 and 1.5, but I will check again, I measured with the Black wire as a common, and each colored wire orange, green and yellow, do those numbers sound right? cant remember right off the excact reading per color just those numbers, I will recheck and get back. Of course the primary was Brown Red and blue, typical.

Thank you for your help!

Ed

[edge59]

Is there a way to post a pic of the tranny here?

thanks!
Ed

[The Dude]

Most likely your resistance reading will correspond to 4, 8, & 16 ohm taps with black ground as you suspect (the largest being 16). I would feel safe enough myself trying it. It would still be helpful to know what the input to the transformer was (I. e. a quad or a pair of 6L6's) because if you do something outside it's original intent, you may need to adapt your outputs.

You can post a picture by clicking the "Insert Image" icon in the Quick Reply window. From there, it's pretty self explanatory, but let us know if you have trouble.

[edge59]

Ok, I will get a pic and post it, I will be using a couple 6CA7's and the screen grids are like 1.5k each, I wanted to put this in a Music man HD-65, and am trying to avoid buying the expensive Music man replacement, hopefully the Bassman trany wil work, I will be selling it, but I want it to work for the guy buying it.

Thanks
Ed

[Tony Bones]

DC resistance measurements will not get you where you want to go. You need to use AC. Read the link provided by The Dude.

You will use DC resistances to identify the primary and secondary windings with certainty.

The primary wires will all have continuity between them.
The secondary wires will all have continuity between them.
There will be no continuity between the primary and secondary. i.e. open circuit which might show up as megaohms of DC resistance on your meter.

The primary will be three wires with hundreds of ohms of resistance. The two with the greatest resistance are the ends of the primary.
The remaining wires are secondary and should all show a fraction of an ohm between them. This is as far as those DC resistances will get you. Their relative values are nearly worthless.


So here's what you need to do.

1. Apply AC voltage across the entire primary.
2. Use your multimeter to measure the applied AC voltage.
3. Use your multimeter to measure the AC voltage between all combinations of secondary wires.
4. Use the results to deduce how the secondary wires can be used.

Part 4 might be confusing, so do 1 through 3 and post the results here. We'll help you with 4.

Trust me. Without manufacturer instructions, this is the only way to know for sure what you've got.

[edge59]

DC resistance measurements will not get you where you want to go. You need to use AC. Read the link provided by The Dude.

You will use DC resistances to identify the primary and secondary windings with certainty.

The primary wires will all have continuity between them.
The secondary wires will all have continuity between them.
There will be no continuity between the primary and secondary. i.e. open circuit which might show up as megaohms of DC resistance on your meter.

The primary will be three wires with hundreds of ohms of resistance. The two with the greatest resistance are the ends of the primary.
The remaining wires are secondary and should all show a fraction of an ohm between them. This is as far as those DC resistances will get you. Their relative values are nearly worthless.


So here's what you need to do.

1. Apply AC voltage across the entire primary.
2. Use your multimeter to measure the applied AC voltage.
3. Use your multimeter to measure the AC voltage between all combinations of secondary wires.
4. Use the results to deduce how the secondary wires can be used.

Part 4 might be confusing, so do 1 through 3 and post the results here. We'll help you with 4.

Trust me. Without manufacturer instructions, this is the only way to know for sure what you've got.

Ok, here is what I have. I used my Variac and set it to 5VAC across the Brown and Blue wires on the primary side. On the secondary, with Black as common, Green=107.2, Yellow=149.4, Orange=211.4 VAC. Did I do good? Also should be attached pics of the tranny.
Thanks
Ed

[edge59]

Was that Millivolts? Maybe I need to do that again...

[Tony Bones]

Ok, here is what I have. I used my Variac and set it to 5VAC across the Brown and Blue wires on the primary side. On the secondary, with Black as common, Green=107.2, Yellow=149.4, Orange=211.4 VAC. Did I do good? Also should be attached pics of the tranny.
Thanks
Ed

That's enough to make sense of things. The impedance ratio from primary to secondary is the square of the voltage ratios.


color voltage ratio impedance ratio

green: 5V/0.107V = 47 47^2 = 2200
yellow: 5V/0.149V = 34 34^2 = 1100
orange: 5V/0.211V = 24 24^2 = 560


I rounded to two significant digits because we're just kidding ourselves if we think we know the measurements with greater precision than that.

Anyway, let's do some educated guessing. The three taps are probably 4, 8, and 16 ohms. Suppose we put a 4 ohm load on the green wire, 8 on the yellow, and 16 on the orange:


green: 2200 * 4 ohm = 8800 ohm
yellow: 1100 * 8 ohm = 8800 ohm
orange: 560 * 16 ohm = 9000 ohm


So it makes sense. If you had actually measured the voltage across the primary then I'd have more confidence in the calculations. I doubt very much that you really get 5V when you set your variac to 5. I wouldn't be surprised if it was actually closer to 3.

edit:Why is it so much to ask for a font that allows formatting into columns to make simple tables?

[edge59]

That's enough to make sense of things. The impedance ratio from primary to secondary is the square of the voltage ratios.


color voltage ratio impedance ratio

green: 5V/0.107V = 47 47^2 = 2200
yellow: 5V/0.149V = 34 34^2 = 1100
orange: 5V/0.211V = 24 24^2 = 560


I rounded to two significant digits because we're just kidding ourselves if we think we know the measurements with greater precision than that.

Anyway, let's do some educated guessing. The three taps are probably 4, 8, and 16 ohms. Suppose we put a 4 ohm load on the green wire, 8 on the yellow, and 16 on the orange:



green: 2200 * 4 ohm = 8800 ohm
yellow: 1100 * 8 ohm = 8800 ohm
orange: 560 * 16 ohm = 9000 ohm


So it makes sense. If you had actually measured the voltage across the primary then I'd have more confidence in the calculations. I doubt very much that you really get 5V when you set your variac to 5. I wouldn't be surprised if it was actually closer to 3.

edit:Why is it so much to ask for a font that allows formatting into columns to make simple tables?

That makes sense, at least I thought the orange was 16 oms, lol! Thank you all so much for helpgng me get this figured out, you guys are awesome!