shbamac
125 posts
Jun 26, 2011
7:46 AM
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Looking at the picture from left to right assuming common, 4 and 8 ohm... Can anyone confrim? Thanks
Using my phone and doesn't look like the pic is showing up here's a link to the pic
https://picasaweb.google.com/m/zoom?source=mog&hl=en&gl=us&uname=lanceposey&aid=5622524805579119521&id=5622524806845426930&viewportWidth=480&viewportHeight=268
Last Edited by on Jun 26, 2011 7:53 AM
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5F6H
746 posts
Jun 26, 2011
8:10 AM
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Can't see the image.
The common tap will connect to chassis ground (if installed in the chassis), check with an ohmeter/continuity test. The two wires with the highest dc resistance BETWEEN THEM are the common & highest ohm tap (if out of the chassis), it doesn't really matter which way you connect them as the 1432 has no negative feedback loop. The wire that shows the lesser resistance to common & highest ohm tap should be the 4ohm tap.
The 4ohm tap is typically used. Schem shows a third tap, which is likely to be 8ohms...however, it would be good to check (budget amps often used surplus transformers & parts changed like the weather). Do you have a low AC voltage source (<6.3VAC) & are you safe to carry out a couple of voltage readings?
Last Edited by on Jun 26, 2011 9:39 AM
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shbamac
126 posts
Jun 26, 2011
9:04 AM
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Thanks for the info. Don't have a low AC source and don't know enough to carrying out voltage readings. The chassis isn't grounded but looking at it a little closer the center tap is connected to the chassis. Just did a quick check with an ohm meter and left to center reads 4 ohms, right to center reads 6 ohms and left to right reads 3 ohms.
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5F6H
747 posts
Jun 26, 2011
9:28 AM
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The chassis is the circuit ground, you don't need to be connected to the wall AC to check for the OT secondary common wire...in fact, resistance tests are safest when unplugged from the wall.
Despite it being a relatively low powered amp, 6ohms (or even whole ohms) accross the speaker connections sounds rather iffy, OT secondaries usually measure well under an ohm.
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shbamac
127 posts
Jun 26, 2011
10:46 AM
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Sorry, that should have been .4, .6 & .3 ohms.
I know that the chassis is ground but the amp still has a 2 prong power cord. Doesn't that mean that the chassis isn't grounded?
No I never checked resistance with an amp plugged in.
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5F6H
749 posts
Jun 26, 2011
11:00 AM
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"Sorry, that should have been .4, .6 & .3 ohms." Good, that sounds more reasonable.
The chassis isn't connected to wall AC ground, but the wall AC ground just ensures that the potential at the chassis is the same as mains ground, so that voltage does not build up ont the chassis, potentially shocking you. The operating voltages in the amp still see the chassis as ground potential compared to B+ voltage. If you stick your black probe on the chassis & check the OT secondaries you will still see zero ohms (or meter default like 0.3ohms) when you touch the red probe to the OT common wire.
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shbamac
128 posts
Jun 26, 2011
11:39 AM
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Good deal. Thanks again for the info.
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