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Old 31st December 2010, 11:42 PM   #1
xbartx is offline xbartx  United States
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Default Any thoughts on what damage I did?

I was trying to convert an old Akai M7 reel-to-reel into stand alone amps. My DIY experience was pretty limited. When attaching the new power cords to the transformer taps, I screwed up and had one amp with the leads at the 110v tap and the other at the 117v tap ( the amps was wired a little different from each other and I didn't notice) I thought I had one lead on the common tap. Something on the underside shorted, I quickly turned the power off.
Now I need help figuring out the damage, Looking at the schematic, knowing what I did, can someone suggest where to begin looking. I have the one amp working and think I should be able to swap out suspect components with ones from my good amp.
-Brad

Akai M7 Left Schematic.jpg
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Old 1st January 2011, 01:41 AM   #2
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Putting 120Vrms across a winding that's expecting 7.0V probably poofed the power xfmr.

That's why it's always a good idea to power up for the first time with a Variac, or at least a light bulb in series with the AC mains connection. You can catch just such errors before you poof something.
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Old 1st January 2011, 08:45 AM   #3
M Gregg is offline M Gregg  United Kingdom
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Hi,

If you are sure that every thing is OK. Please be carefull of stored charge! Never pull tubes or replace with power on!

Remove the rectifier tube set your test meter to AC volts.

Power on.

Test incomming supply, heater supply and High tension supply only the AC will be on B+ "should" be dead. Heaters should come on!

Power off.

Let us know what you get! Only power up as long as necessary for tests. Always test for stored charge before touching.

Regards
M. Gregg
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Old 1st January 2011, 02:24 PM   #4
Sheldon is offline Sheldon  United States
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As Miles said. That why fuses are used. If it wasn't fused, and the wiring external to the power transformer is intact, you almost certainly fried at least the 117V tap. And you probably damaged the internal insulation of the transformer. You can check by measuring the resistance between the 0 and 117V taps. I suspect it will be open. Don't power anything up until you have a working power transformer.

Sheldon
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Old 1st January 2011, 02:40 PM   #5
M Gregg is offline M Gregg  United Kingdom
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With any luck he blew a fuse, if not the 110-117v will be open and the 0-110v will be OK. Otherwise it's a new Tx.

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Old 1st January 2011, 03:24 PM   #6
xbartx is offline xbartx  United States
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I don't have any open readings!
I'm really just learning and I spent a decent amount of time just trying to figure out terminology. Is the heater supply the cropped schematic I've attached and the blue wires attached to the 6.3V 1.8A taps?
I not sure what/where the high tension supply is.
Is the "rectifier tube set" the power tube in this case the 6BQ5?
There were no fuses, I will put some in now.
I sure have a lot to learn.
-Brad
_DSC4553.jpg
heater.jpg
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File Type: jpg heater.jpg (20.5 KB, 90 views)
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Old 1st January 2011, 03:29 PM   #7
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I would think that the 110-117 tap (which would be wound as part of the 0-110 winding) would have the insulation fried which would probably have damaged the 0-110 winding. But let's hope for the best.
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Old 1st January 2011, 04:04 PM   #8
M Gregg is offline M Gregg  United Kingdom
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xbartx,

I guess you are not sure what to do!
Just a quick check with power off do a resistance check from 0 to 110v connection and a test from 0 to 117v connection tell us what you get!

Do you have a multi-meter?

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M. Gregg
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Old 1st January 2011, 04:15 PM   #9
M Gregg is offline M Gregg  United Kingdom
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The rectifier is the 6x4
yes the cropped pic is the heater.
Lets keep the tests with power off

It is hard to see from the pic where is the mains connection is it behind the red wire?

The high tension is the high voltage B+
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Old 1st January 2011, 04:38 PM   #10
M Gregg is offline M Gregg  United Kingdom
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XbartX,

I need to ask please don't take this personal how old are you?
Have you read the safety section in the sticky thread?

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M. Gregg
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