Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on July 18, 2015, 02:31:24 pm
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Still believe I blew up my OT when one of the legs came disconnected during play. After reattaching and installing new grid resistors, turning on the amp yields some Tesla looking lighting bolts inside one pair of the EL84. I do still want to test it. I like the 1 VAC approach on the primary while measuring between CT and each leg, then across both legs.
Is this efficient? A good way to determine? If so....best wa to get 1VAC??
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1v AC on the primary .... to me sound a very low voltage for the primary if you measure on the secondary you find a very very low voltage and may be your tester isn't so accurate on that measure
To me 100v on primary is a better choice or use a 6-6.3v voltage on the secondary and measure on the primary
As to test a transformer there is also one other trick to be used in junction with the trasformation factor measurement
(http://www.vintage-radio.net/forum/attachment.php?attachmentid=40460&d=1284535236)
K
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Thanks k.
If I put 6.3 volts on the secondary, I'm assuming I would expect a lower voltage on the primary. Is this a correct assumption. The way I understand it is this.
Apply a voltage. Check on the other. Say you get roughly 10v from each leg tested to center tap, you should get roughly 20v across both legs. If one leg yields a much lower voltage than the other, it's a good chance there is a problem there.
The videos and tests I've seen, they use 1v on primary. The secondary shows 20 on each leg and 40 across. Wouldn't I get the same results if I used about 6vac and did the same test?
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If I put 6.3 volts on the secondary, I'm assuming I would expect a lower voltage on the primary. Is this a correct assumption.
No, it's just the opposite. Put a voltage on the primary and that will be stepped DOWN to a lower voltage on the secondary. Put a voltage on the secondary and that will be stepped UP to a higher voltage on the primary.
Just like a simple filament transformer. Put 120VAC on the primary and it will be stepped DOWN to 6.3VAC on the secondary.
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I assumed that was the case based off of the fact that the OT takes the high voltage low current and steps down to low voltage higher current. But in my reading I could have sworn they worded it the opposite. They may have and misspoken or maybe I misread. But thanks Sluckey. That makes more sense.
So anyway, say I put 3.15 lead on common of secondary and 3.15 on say 8ohm tap, I would expect a higher reading on the other side of XFMR? If this is correct application, should I test same setup with 16 ohm tap as well. And 4 if applicable? I've never encountered this but I assume it's possible for 8ohm winding to be bad and 16 still functional?