Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silat on June 24, 2016, 09:52:31 am
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Can you help me identify the wiring on this old pt ? It is very different from what I am use to seeing color wise.
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I am thinking black is primary and the yellow red is a center tap. One of those yellow pairs is 5 volts and the orange 6.3 . or that may be faded red and it's high voltage :BangHead:
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Measure resistance.
120V winding on iron that size will be 5 or 10 Ohms.
B+ AC will be nearer 100 Ohms.
Heater windings will be sub-Ohm.
Heater windings may be fatter wire, and I see such in the picture.
With a provisional guess, apply 6VAC (from another amp's heater supply) to the presumed "120V" winding. All other voltages should be 1/20th of what you guessed. A 700VCT winding will give 35V, startling but probably not fatal (still I would not use fingers, use clip-leads). 6V winding gives 0.3V. It may be hard to tell 6V from 5V (0.3 vs 0.25), but you can sort that out when you know you have the 120V and 700V sorted and it is safe to apply full 120V (but use lamp limiter!).
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Thank you PRR.. I appreciate you answering so quickly!
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I got 34. 2 on the redish looking wires so I am assuming they are the HV from hooking the black that I assumed were the primary's to my other amp with the clip leads just like you said PRR .
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Whee can I find the voltages to his layout?
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Maybe ask over on the Weber forum. Or look up the specs for that PT to get a general idea about voltages. Or look at a Fender Deluxe Reverb because that amp is a clone of the DR.
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I don't think that will help much because I used the iron out of my conn organ Amp.
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I don't think that will help much because I used the iron out of my conn organ Amp.
I think it would be very helpful to know the rating on that PT. Then you could measure the voltages on your PT and make a comparison.
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I think it would be very helpful to know the rating on that PT. Then you could measure the voltages on your PT and make a comparison.
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Ok Thank you!
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here's the specs on the W025130 PT http://www.tedweber.com/media/import/w025130sch.JPG (http://www.tedweber.com/media/import/w025130sch.JPG)
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Looks very straightforward to me.
Blk-blk = 120 VAC DC measured resistance typically 2-5-10 ohms.
Yel-yel = 5VAC (measured resistance will be really low, less than 1 ohm)
Red-red = HV Red yel CT (measure roughly equal resistance between red-yel and either red wire) red-red resistance can be ~~100 ohm-250 ohm
The remaining browns are your 6.3 VAC, should also measure very low, less than 1 ohm
The 5 VAC and 6.3 windings will almost seem like shorts.
We also take a clue from the LENGTHS of the wires. We expect the 5 VAC wires to be just about the same length. Same with the 6.3 volt, same with the HV but not necessarily the HV CT.
One of the safest way to tell if you are unsure is to find an AC wall-wart (HAS TO BE AC and MOST ARE NOT!) and power up the alleged primary with the AC out of the wall wart. Let's say the wall wart is 15 VAC. Then each secondary should put out 15/120 their normal volts. Thus a 5 volt winding should put out 15/120 * 5 = .625 volts. The 6.3 winding should put out a little closer to .8 volts.
The HV winding can still give you a shock under these conditions, 15/120 * 325-0-325 = 15/120 * 325 = about 41 volts across half or 82 volts across the whole (red to red) winding. I ALWAYS make these tests from one leg of the HV to the center tap so I am measuring half the HV. You want to have alligator clips on your meter tests leads. You also want to be a little careful connecting up the primary side, don't get finger-lazy because "it's only 15 volts" because when the power goes off, the collapsing field can generate what might be a surprisingly highish spike.