Headphone Trick for PT / OT Inductance

[abonf088]

Hello all,

I'm attempting my first champ build & a little confused about the headphone trick. I'm using Hammond 290ax PT & 125dse OT. My question is, how do I correctly wire this up to the power cable? AX84 instructions say to tape off all secondaries( done) & connect 2 primaries to the power cable. I'm in Canada running 120, so would I only need to connect 1 primary to the hot of the power cable? (each primary is 120v) & what do I do with the neutral & ground of the power cable? There isn't a ground on this PT & don't I need to ground it? I don't want to blow up a tranny on the first build, I'd have a hard time explaining that one to the wife.

Thanks

[Meat&Beer]

Try this here like here;

http://aga.rru.com/FAQs/build.html#ot_pos_1

Hope it gives you some answers. I'm sure some actual smart guys will wander along and chime in soon.

[abonf088]

That does help, thanks. However what do I do with the ground & neutral from the ac power cord? Just tape them off as well?

[Meat&Beer]

4th bullet under the #8:

"Wire the PT primaries to a power cable."

So ground from the power cable is going to the chassis, then, + & - of the cable go to your PT primaries.

That's what it's saying to me, anyways. You still might wanna wait for a more knowledgeable/credible source however. I'd hate to have something nasty happen because of me....

[abonf088]

Thanks again, that's what I was thinking. Of course I'm not 100%. As for waiting for a better source... the waiting is killing me. I guess that's what I get for telling my wife not to worry & that I know what I'm doing.

[Meat&Beer]

Haha! Exactly.

Also worthy of mention, I believe that when people do this "trick" the PT is already mounted, and the OT is moved as to find its sweet spot. This being the case, I'd recommend having the fuse and switch in line with the PT also installed in the chassy.

Also, be aware of the secondaries! Be safe is all, none of us like getting whacked.

Take your time, and all will be happy rainbows of glowing fairy dust inside pretty little glass envelopes.

[xtian]

Hello. I've done this many times. Yes, carefully tape off ALL the PT secondaries, everything except the two primary wires for the 120v coil. You want to connect one PT primary wire to your "hot" ac wall voltage, and the other PT primary wire to your "neutral" ac wall voltage (if you connect only one wire, you won't have a circuit!). If you're using a three-conductor mains cord, you don't have to connect the green "earth" or safety ground to anything.

You can do this whether none, one or both of the transformers are mounted to the chassis.

Your OT should be connected ONLY to headphones or scope, nothing else.

[Meat&Beer]

Nice!

[Phil_S]

... tape off all secondaries( done) & connect 2 primaries to the power cable...

There is one primary coil. There are two wires, one at each end of the coil. They should both be black according to the wiring diagram. Using a 3 prong wire to the wall socket means the green wire gets grounded to the chassis. The + (black) should be fused. The - (white) does not need to be fused.

You might as well wire it up to the switch and fuse while you are up to this.

[abonf088]

thanks for the help. I'll give it a go.

[abonf088]

Thanks everyone, just finished. that was pretty cool. My original OT position was pretty good but I think I may have quieted it down a tiny bit more.

Cheers!

[davent]

I put a small box together to take care of the transformer leads and headphone jack. Saves the hasssle of trying to jerry-rig it all up every time.

Where in Ontario?

[IMG:600:800]http://i216.photobucket.com/albums/cc305/davent/IMG_2502.jpg[/img]

Eventually ended up with the transformer mounted on a bracket, horizontal.

[Tillydog]

A general point...

Don't forget that it's the AC mains power we're playing with here which is arguably more likely to kill you dead than anything else inside the amp:

Make sure that all the AC connections are properly insulated;

The metalwork of the power transformer should be connected to the ground/earth of the AC supply (e.g. bolt a solder lug to one of the mounting holes on the transformer).

That is all.

/preachy

[abonf088]

Davent:

Thats a pretty neat test box, another project for me. I'm in Brighton Ontario, how bout you?

Tillydog:

ACK on connections & grounding.

All:
Another question; I just noticed I have 2 mono input jacks instead of shorting jack. What is the purpose of the shorting jack? Should I get shorting jacks? & are they the same as a mono jack with switch.

thanks again

[xtian]

You want shorting jacks for the inputs. When you remove your guitar plug, you want the tip to get shorted to ground so you don't get an ugly BUZZZ when you unplug your guitar from the amp.