Transformer confirmations

[Mark]

I’m using a Hammond TF22772 PT and Classic Tone 40-18031. Can someone confirm that the color scheme in the layout matches these transformers? It appears the red and grey on the OT are not used, correct?

Thanks!

[Mark]

To be clear, the Classic Tone is the OT 😉

[Andy]

I haven’t heard of anyone on the forum using the Classic Tone Output Transformer. It would appear that you use the Blue and Brown on the input side. The output side is fully dependent on the speaker combo and impedance total of those. And on the tube you are using. Check the chart in the book.

It looks like the GRAY on the Classic Tone is the same as the WHITE on the spec’d Hammond 125ESE.

[Mark]

Thanks again Tan! So the input impedance should be 5Kohm then right, if I’m using the blue and brown leads? The secondary looks like it’s just a matter of matching the speaker impedance. In my case, I’m using a 6V6 output tube and 5Kohm primary impedance on the OT, and an 8ohm speaker. So the I should use the black and green secondary wires for the output jack, correct? Here’s a link to the Classic Tone spec sheet:

http://www.classictone.net/40-18031.pdf

I really appreciate your help!

[Andy]

That looks right on this OT!

[Mark]

So I just realized that the PT is actually the one from Antique Electronic Supply, the one that is listed in the book along with he Mojo and Weber ones. I looked up the specs on it and it says it has a 2A filament supply instead of 4A, like the others. The book specifically refers to the filament having a 4A spec. So, is 2A going to be enough? Why is the AES PT recommended if it doesn’t have a 4A spec filament supply?

Another question is that this AES supply only has a Red/Yellow lead, so I’m assuming it has a center tap and doesn’t require an artificial center tap correct? I just connect the Red/Yellow lead to ground, right?

The spec on this PT are here:
https://www.tubesandmore.com/products/transformer-fender-replacement-power-325-0-325-v-70-ma

[Mark]

To be clear, I’m referring to the filament supply to the pilot lamp, 6V6, and 12ax7. It’s only 2A.

[Andy]

I don’t have the book in front of me but that is the PT that we use in the kit as well. 2A is plenty to run the filament supply, that does not draw that much current.

For the filament center tap, you will need to make an artificial one. For some reason, the new PTs removed the filament CT. This is done by attaching a 100Ω resistor from each green filament line to ground. I usually attach it at the 2 pilot light terminals and ground it at the 3 pin ground terminal. I’ve attached an image so you can see what that looks like.

The red/yellow is as described in the book.

Attachments:

1. 

   CenterTapReplacement.jpg
   

[Mark]

Thanks again Tan! Sorry, I guess I don’t understand what a center tap is. I’ll wire the green pair as you say.

There is no green/yellow wire on this PT. There’s a green pair, red pair, yellow pair, black pair, and a red/yellow. I on the book layout, it shows the green/yellow in parentheses “(green/yellow)”. I assume that means that a green/yellow may or may not be there, correct? I just connect the red/yellow to ground and forget about the green/yellow.

[Mark]

Also, how many watts should those 100ohm resisters be?

[Brent]

I don’t know why you couldn’t use 1/2 watt resistors for the artifical center tap, but I use 1 watt.

[Andy]

Correct. The Green/Yellow is the center tap but since many new production transformers don’t have a center tap on the filament secondary, we create the artificial center tap with the 100Ω resistors.

As far as wattage, I like to stay at 1W for safety. Typically, I use 1W throughout the build as they are quieter, except in places where more wattage is called for (ie the power supply ceramics). The kit we supply uses 1W throughout to reduce the overall noise.

[Author]

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