Mercury magnetic OT - dead on arival I think

[yalesmith]

I just completed a Liverpool build and no sound.....the OT transformer makes a very odd rattling sound but no signal. I have 3 questions....first, I was thrown a little because it had 2 primary taps...so I used one set and wire nut the tap i don't use seperately, I don't have 2 ground those do i? 2nd, how common is it it to get a dead transformer? especially a mercury Mag? and last is there an easy way to check to determine if the ot is dead?

Thanks

[leadfootdriver]

Could you post a pic of the wiring diagram that they included with the tranny?

[Clyde]

Very unusual. Was there not a schematic diagram with the transformer to follow? Which model was it? To check, use a VOM and measure resistance on both the primaries and the secondaries.

[bluefireamps]

Is this a Vox style OT? Does the primary have 4 wires? Some Vox OT's had two separate windings, one for each "side". Two wire need to be connected together to form the center tap. Get a hold of MM to get a proper wiring diagram before doing anything else.
Dave

[Colossal]

first, I was thrown a little because it had 2 primary taps...so I used one set and wire nut the tap i don't use seperately

If you are using Mercury's Dynaco clone, the GREEN wires on the primary side are the ultra linear taps. You don't want to use them. Wire tie and shrink wrap them up. You want to be using the BLUE and BLUE/WHITE wires for your primaries.

I don't have 2 ground those do i?

No! Hopefully you did not run the OT with them grounded?

2nd, how common is it it to get a dead transformer? especially a mercury Mag?

Highly unlikely

[yalesmith]

I have the ot schematic.....it has 2 primary's a 5,2k (brown and blue wires) and a 6.8k (brown&white & blue /white wire). I am using the 5,2k primaries.

[yalesmith]

and i have not run them to ground.
thanks

[eazilyled]

You probably ruled this out but is the speaker cable / speaker cab wiring known to be good?

I only say this because you mentioned that the OT is making a strange noise, and I was wondering if it was 'singing' along with the signal which can be normal under heavy signal (I believe magnetostriction is the official name for this).

[Colossal]

I have the ot schematic.....it has 2 primary's a 5,2k (brown and blue wires) and a 6.8k (brown&white & blue /white wire). I am using the 5,2k primaries.

Ok, so that's Mercury's standard TW-KF-OT, not the Dynaco then. Yes, the 5k2 primaries are the right choice.

and i have not run them to ground.
thanks

Excellent!

As for troubleshooting...

1) Have you tried the aforementioned test of the OT primaries and secondaries? You can apply a known DC voltage to the primary side and measure the secondaries to make sure there are no shorts.

2) Have you double-checked your speaker jack and OT ground? If you are using a Cliff style jack, make sure the signal is going to the tip and not the tip switch (sending your signal to ground!). You've probably checked some of this stuff, but figured I'd mention it. Sometimes you can look at something a dozen times and it looks right but can be subtlety wrong.

[yalesmith]

Not the transformer, I threw it in an express and it work perfectly. Back to the drawing board... I will a/B the mercury and the pacific transformer and report back.

thanks

[Tillydog]

You can apply a known DC voltage to the primary side and measure the secondaries to make sure there are no shorts.

Just a typo catch: Make that *AC* voltage

Andy

[Colossal]

You can apply a known DC voltage to the primary side and measure the secondaries to make sure there are no shorts.

Just a typo catch: Make that *AC* voltage

Andy

Whoops! Thanks Andy, yes AC.

[rooster]

Also, FWIW, when using a Cliff jack, or switchcraft for that matter, it doesn't matter which end of the secondary you ground, the OT will work. You will need to reverse the PI however if things are reversed and you are using NFB. It's just a coil of wire, afterall.

OK, wait, I see that Colossal was warning you about wiring the hot side of the secondary to the Cliff jack lead that was not connected to anything if a plug was inserted in the jack. I see the intent now.

[yalesmith]

My bad, I swapped out the tranny and threw it into a build I know works and bam it is all good. With 2 tranny's I decided to compare the MM and the Pacific OT. First, the MM sounds better no doubt, no matter if you use the 5,2 or 6.8k primaries. But the Pacific has a character that makes it unique. There is an added crunch of sorts but MM is clearer. MM makes is sound like a Mark VI/Soldano SLO and the pacific makes it sound like an engle/dual rec. I have played or own all of the amps listed.