Need help choosing correct Hammond transformer for Real McTube

[Esppse]

Hey,

I did a lot of research and found many open style chassis mount transformers, but I'm looking for those enclose, tube amp like transformers. I think I located them here. I've never worked with anything that deals with 120v, so this is newer territory for me.

So the schematic here calls for 2 transformers.

https://i.pinimg.com/originals/f6/69/42/f6694272eee42f9d00067740b39dba82.jpg

Do I buy 2 of these? Im willing to shell out a bit more for these enclosed style ones. It says primary voltage is 115VAC, and secondary is 12.6VAC. I'm unfamiliar with these terms, and am curious if these are perfect for the McTube.

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/167N12?qs=AeBljyeJo%252bgYLSihSCPbgw%3D%3D

Thanks

[thermionix]

Are you in the US (or somewhere else with ~120VAC wall juice)?  If so, two of those Hammonds will work.  They're rated for 8x as much current as the schematic specifies, so bigger and beefier than necessary.  You also don't need the CT (center tap) but you can just tape that up.

[Esppse]

Ah thank you so much. Yes I'm in the US. Can't wait to put this unit together, definitely the most dangerous project to cross my bench yet!

[thermionix]

I've never worked with anything that deals with 120v.....I'm unfamiliar with these terms.....

I guess it would behoove me to say, if you're not 100% sure of what you're doing, don't mess with potentially lethal voltages.  Do a bunch more reading before attempting this project.

[thermionix]

^ Simulpost (I type slow).

Can't wait to put this unit together, definitely the most dangerous project to cross my bench yet!

Please don't rush this.  You need to understand what the Primary and Secondary are.  If you hook that up backwards, you'll have about 1000VAC coming out.  Hook to the CT, maybe 2000V.

[Jeema]

The other issue is that this transformer is rated at 12.6V when delivering 50W of power.  If it's delivering less power than that (which it definitely would be in this circuit), then the voltage will be higher - probably around 17V with this circuit would be my guess.  So you'd need a power resistor to drop the tube filament voltage back down to 12.6V.

Probably easier to just go with smaller transformers to be honest.  There's a number of ones on Mouser that are through-hole style if you don't like the open chassis ones.  I don't particularly like the open chassis ones either.

[Esppse]

^ Simulpost (I type slow).

Can't wait to put this unit together, definitely the most dangerous project to cross my bench yet!

Please don't rush this.  You need to understand what the Primary and Secondary are.  If you hook that up backwards, you'll have about 1000VAC coming out.  Hook to the CT, maybe 2000V.

I'll definitely be careful with this. I've soldered the tiny transformers for things like a varitone, the mouser xicon, which labels P for primary. Thanks for the caution.

[Esppse]

The other issue is that this transformer is rated at 12.6V when delivering 50W of power.  If it's delivering less power than that (which it definitely would be in this circuit), then the voltage will be higher - probably around 17V with this circuit would be my guess.  So you'd need a power resistor to drop the tube filament voltage back down to 12.6V.

Probably easier to just go with smaller transformers to be honest.  There's a number of ones on Mouser that are through-hole style if you don't like the open chassis ones.  I don't particularly like the open chassis ones either.

Hmm, didn't think of that. I wasn't sure I would need to modify the schematic. Is the power resistor indicated or included the the schematic shown? Can you point out to me where it would go?

Thank you

[GibsonGM]

The heater dropping resistor could go between T1 and the point on the board marked "A" just fine, or offboard over by the tube; it would not have to be on the PCB (in fact may be better OFF the board, to dissipate heat, which you'd need to keep an eye on.  This is where knowing 'what's going on' comes in, or you could burn something up/cause a fire, literally).

Best idea is the smaller transformers as mentioned; but if you want to use the bigger, you will need to safely hook them up first, then see what their AC voltage is at the secondary of the 1st one (says "12 V AC" on the schematic).   Using Ohm's Law, you would calculate the value resistor needed to drop the X surplus volts.  Or you'd come back here and post the AC voltage you measured, and someone will help you do that, AND to size the resistor properly for the heat (power) it must dissipate     Too high a voltage burns out the tube heater; too low a power rating burns out the resistor.

PS - any questions as you try putting this together, don't hesitate to take a break and ask for advice on here if you don't know something!  MUCH better to be safe than sorry, even on the 12V end of the transformer; they are still hooked up to line voltage and can kill you!

[Esppse]

OK thanks very much, I'll definitely play it safe and ask questions before I do anything I'm not 100% sure of, I'm saving funds to do this project and hopefully get to it soon. Nice to know I've got support behind this project, much appreciated!

[Rob Strand]

You should read this,
http://sound.whsites.net/psu-wiring.htm

[davent]

I've used the Hammond 164 series of transformers for a a couple complete tube amps, they're flatpaks and solder mount to a pcb. According to the pdf want a 6VA  (12V x 0.5A) sized transformer which are tiny and cheap.

https://www.mouser.ca/ProductDetail/Hammond-Manufacturing/164F12?qs=sGAEpiMZZMvwUzoUXIIvyQPvPmwnNFGyjyoHOPSmP9s%3d

dave

[davent]

To keep 120VAC out of the enclosure you could use a 12VAC wall wart to power the second transformer inside the enclosure.

http://www.audioxpress.com/assets/upload/files/stamler2874.pdf

dave