PT Specs – Hammond

[LesEpi]

:blink: Hi there. Wondering if someone might be able to clarify this for me. The schematic for the two stroke Rev. 1/13/2011 by TAN notes secondary voltages of 275VAC. However when I read the Parts List for the two stroke it lists a weber W022772 which has red-red 330v-0-330v see spec sheet here http://taweber.powweb.com/store/022772sch.jpg%5B/url%5D
I have an in on hammond parts and am wondering which PT I should get from them. This is a link to their replacement PTshttp://www.hammondmfg.com/guitarLinePWR.htm%5B/url%5D I was thinking the 290AX would be similar to the weber/heyboer 022772. I believe the 290ax specs are 325-0-325. It is a drop in replacement for a champ. Are the 275-0-275 voltages in schematic erroneous?

[Andy]

Yes that 290AX is a good fit.

BTW, the Webers are made overseas. Mojotone is using Heyboer to make their transformers.

I will check the schematic, 330V is what it should be, but there are some older schematics out there that has 275. I’ll look into it.

[LesEpi]

Hey AJ. Thanks for the reply. This was the schematic I had. I downloaded it from the Wiki page
https://www.tubeampnetwork.com/images/TwoStroke_TAN.jpg%5B/url%5D

[Robin]

The Fender 022772 specs 325-0-325 70mA for the B+ voltage. All the 022772 PTs I’ve seen are in the 325-330v range and work great in the Two Stroke (and a bunch of other small amps). Heyboer makes great transformers as does Magnetic Components, Mercury and Hammond. I’ve used a few of the imported Weber 022772 transformers and had great luck with those as well. BTW, 275v might not be bad either, especially with a solid state rectifier.

[LesEpi]

Should I be concerned about a lack of ct on 6.3V winding? Or is there some kind of work around for that? I understand the ct there is to minimize noise?

btw, that recording Robin posted makes me want to build this amp even more!

[Andy]

Most of the transformers that we can get these days has that Center Tap removed. It is important to include 2 100Ω resistors in the circuit. It has been covered elsewhere, but basically, the two green leads from the Power Transformer run to the pilot lamps.

The 100Ω resistors go from each leg of the lamp to ground. The TAN Kits do the same thing.

[LesEpi]

Thanks again, that helps.

[Robin]

A center tap is nice but the artificial tap is easy to add (and it makes a big difference in hum control). check out the “Valve Wizard” website, there is a great page on heater circuit design and center taps.

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