Need help with preamp power x-former selection PLEASE!!!

[JGR]

Hey guys,

I need some help selecting a power transformer for a tube preamp I'm building. It will have three 12ax7's and I would like to fit it into a 1 rack space chassis that I have, so max height can't be more than 1.5 inches. I was thinking of a toroid for packinging and hum considerations. Hammond was the easiest to find, but if you have any other recommendations, please let me know. From the Hammond's listed below, can you help me pick which one might work best? I was thinking the 182B240 but I'm not sure if the current rating is high enough?


No. VA VAC Secondary (RMS) Dual or Single Secondary
182K6 15 12V ct @1.25A 6V @ 2.5A Dual A
182H9 15 18V ct @ .83A 9V @ 1.66A Dual A
182G12 15 24V ct @ .63A 12V @ 1.26A Dual A
182G15 15 30V ct @ .5A 15V @ 1A Dual A
182F18 15 36V ct @ .42A 18V @ .84A Dual A
182F22 15 44V ct @ .34A 22V @ .68A Dual A
182D110 15 220V ct @ 68ma 110V @ 136ma Dual A
182D117 15 234V ct @ 64ma 117V @ 128ma Dual A
182B240 15 - 240V @ 63ma Single A



Thanks

JR

[stokes]

ThatB240 with 240v@63ma is plenty for your plates,but what are you using for the heaters?Your tubes will draw .3 amps each so you need at least a 1 amp but that would be marginal,I'd feel safer with 2 amp.

[JGR]

Got it, thanks. I was going to use a separate filament transformer for the heaters.


JR

[Tobacco Soup]

KOC showed an interesting schem in TUT2 that could be applied here. However, it will increase parts count and expense:

Simply 'stack' a 300V-ish P.S. with a 200V-ish P.S. for a MAX B+ of 500V. The 'ground' reference of the 300V-ish PS is tied to the positive leg of the 200V-ish PS which is referenced to the 'true' ground. If you're using 1N40007's it's not bad at all, if you're using FRED's then it can get really pricey... HTH!