Laney OT diagnosis

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Laney OT diagnosis

Postby Hamilton » Fri Sep 04, 2009 6:52 pm

Brian, a buddy brought over an AOR 50 watt Laney series 1 that has no sound at the speakers. EL34 plates are at 403 vdc, grids are -34 vdc. I "ohmed" the OT secondary and found no opens, all readings were under ½ an ohm.

When I touch the volt meter to pin #3 on the power tubes there is no click coming from the speaker. The impedance selector *looks* alright but that's all I did was look at it.

Dead/shorted secondary? Anything I'm missing?
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Re: Laney OT diagnosis

Postby Brian Wallace » Fri Sep 04, 2009 9:06 pm

Hammy,

Take a jumper cable and plug it into the output jack. Use this to measure the secondary taps through the selector.

Did you measure the primary? I think I have the tear down info from one of these. Just looked and it was a 100W OT.
Remember....You can fix it with a little extra energy and a positive attitude. ;)
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Re: Laney OT diagnosis

Postby Hamilton » Fri Sep 04, 2009 10:13 pm

Good call, Brinker - primary resistance, each side : 63Ω and 7Ω :D

This amp also has a bad impedance selector, the readings were all over the place. Finally unsoldered everything and got these readings :

Secondary :

brown = .6Ω
orange = .9Ω
red = .7Ω

The sticker on the OT says "Ariel 6010"; it looks very close to a 784-139.
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Re: Laney OT diagnosis

Postby Brian Wallace » Sat Sep 05, 2009 11:26 am

A 139 would probably work fine but the 63 ohm reading is about 20 ohms more than a 139.

What are you going to do with the old OT?
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Re: Laney OT diagnosis

Postby Hamilton » Sat Sep 05, 2009 12:56 pm

I'm not sure I'll be doing anything with the amp, which is fine....don't need the "free work". He's been working on it for a long time and need some help with diagnosis.

You might remember him at the old Plexi Palace, "NATE".
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Re: Laney OT diagnosis

Postby Brian Wallace » Sat Sep 05, 2009 1:12 pm

I remember Nate. :)

Send him over to this forum. :wink:
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Re: Laney OT diagnosis

Postby Hamilton » Sat Sep 05, 2009 6:44 pm

I'll tell him.

Oh, he said he has another OT.

Anyway, I appreciate your expert advice.
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Re: Laney OT diagnosis

Postby Gwyn Davies » Sat Jul 07, 2012 4:41 am

Hi there.I had a similar problem with a Sound City amp in the early nineties.It turned out that the output EL34 valves had no emission at all! This is a VERY unusual occurrence.Sounds to me that the output transformer is fine,Try some new output bottles.Cheers,Gwyn Davies.
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Re: Laney OT diagnosis

Postby Mullard » Sun May 25, 2014 3:25 pm

Finally after a week of bugging the admin. I can respond to this post.
The amp is still messed up and it just sits in the corner of the room. In regards to the tubes, I have swapped them out for known good ones and the issues is still present. The OT and ohm selector have been swapped out and I might put the original OT back in it.

I'm about ready to swap the board out and make this some kind of a JMP50 hot rod circuit since I love my '73 1987.

Thank you all
Nate
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