Trainwreck Output Transormer wiring question

[mehfuzhoss]

Hello,

I am wiring up a hammond OT 125c. My spkr cabinet is 8 ohms and this is how i am hooking it up. please correct me if it is wrong.

https://imgur.com/uEjvEBm


Thank you for your help.

[pompeiisneaks]

No that's not correct. The secondary needs to have one lead connected to the positive side of the speaker, the other is the negative side. The way you have it will burn up the transformer (you're jumpering the secondary windings together, and it will short out the transformer). I'd suggest putting one pin to the 8 ohm jack positive (tip) of the jack and then the other to the sleeve/negative side. You could have phase issues since they don't seem to indicate which is considered the 'negative' but that's easily fixable by swapping the primary side wires inside the amp, or these wires as well. (If there are any negative feedback in the speciffic amp, if not it won't matter, but since you just say trainwreck, the rocket has no NFB but the express does. so it depends on 'which' amp).

~Phil

[mehfuzhoss]

I am building a 2 watt tw 4 4 0 layout from ax84.com

usually OT has wires as black being 0 ohms, green 4, yellow 8 and orange 16.

but 125c has 6 taps instead. i need to find out the '0 ohm' /black wire on this OT to connect it to the negative of speaker. and finally the 8 ohm tap.

i found 125b OT with color coded wire attached to it.
link : https://www.hammfg.com/files/products/1 ... 125b-b.jpg

can i use the same color code for 125c? so that
tap 1 is black
tap 2 is orange
tap 3 is green
tap 4 is yellow
tap 5 is purple
tap 6 is white

to put it simply, i would like to know, on the 125C OT which wire will put out 4 8 and 16 ohms and the 0 ohms.

thank you.

[pompeiisneaks]

From the picture you showed in your first post, you want 8.2k primary impedance and 8 ohm secondary, then you connect the two leads 2 and 5 to either side of the speaker. Or to a speaker jack with one being ground the other positive. If you wanted multiple impedances you'd have to lookup each one and possibly hook them up to different jacks.

~Phil

[sluckey]

First off... Why are you calling this a trainwreck? IT AIN'T! It's an ax84.com 4-4-0.

Now specifically... That 125C transformer is a special case. It can be used with a wide range of primary impedances (translates to many different tube types). There is no such thing as a zero ohm (black wire) or any set impedance wire for this transformer. YOU MUST USE THE CHART TO DETERMINE WHICH CONNECTIONS TO USE. There is also some good info on the schematic. You just need to look at it.

More specifically... ***IF*** you are using 6SN7s for output tubes, you'll want to set the primary for 22.5K. Now, you want to use an 8Ω speaker so just look at the chart, move over to the 8Ω column, drop down until you find 22.5K. Now move to the left and you'll see that you need to connect the speaker jack to terminals 2 and 4. Doesn't matter which wire goes where. Well actually it does. If the amp squeals just reverse the two wires going to the speaker jack.

You should really consider voicing your concerns about this amp over on the ax84.com forum. They are the guys who designed this amp. They are very knowledgeable and friendly.

And stop calling it a trainwreck!

[pompeiisneaks]

Yeah I've moved the topic to technical discussion as it's definitely not a trainwreck. I won't forcibly rename the thread but you should likely edit the name of your first post to remove the incorrect name.

~Phil

[mehfuzhoss]

Yes, I am using a 6SN7 as a power tube. I am looking at the chart and yes the tap 2 and 4 will be connected to the speaker jack positive and negative and i will swap them only if it squeals. Since i do not need other ohms setting i wont' use the impedance switch and that makes it lot easier. correct me if i am wrong.

Thank you very much