Aikido Transformer(s) recs

sts9fan · « **on:** 8 Dec 2008, 01:12 pm »

Hello,

I just grabbed a 6SN7 Aikido/Janus kit from a fellow circler and need some recs on what transformers to use. What seems to be everyones favorite? What are options that are good but will not break the bank? Do you use a torroid on the heater?
Thanks
Kris

TomS · « **Reply #1 on:** 8 Dec 2008, 03:24 pm »

I have one using a Hammond 185C12, 185C230 and a 156L choke to get about 250vdc. Haven't built it yet but Duncan simulation says it should work fine.

sts9fan · « **Reply #2 on:** 8 Dec 2008, 03:41 pm »

cool I think the 12.6vdc one will work for the heater but I need 400-550vdc for the main part. The Janus is tube regulated down to 250-300vdc.

Kris

BillB · « **Reply #3 on:** 8 Dec 2008, 10:12 pm »

Edcor has some pretty nice transformers too.

sts9fan · « **Reply #4 on:** 10 Dec 2008, 05:31 pm »

Quote from: TomS on 8 Dec 2008, 03:24 pm

I have one using a Hammond 185C12, 185C230 and a 156L choke to get about 250vdc. Haven't built it yet but Duncan simulation says it should work fine.

Are you using four 6SN7?

sts9fan · « **Reply #5 on:** 10 Dec 2008, 06:10 pm »

I am looking at the hammond 375x but they are kinda pricey

TomS · « **Reply #6 on:** 10 Dec 2008, 08:38 pm »

Quote from: sts9fan on 10 Dec 2008, 05:31 pm

Quote from: TomS on 8 Dec 2008, 03:24 pm
I have one using a Hammond 185C12, 185C230 and a 156L choke to get about 250vdc. Haven't built it yet but Duncan simulation says it should work fine.

Are you using four 6SN7?

9-pin 6cg7's in mine

sts9fan · « **Reply #7 on:** 10 Dec 2008, 09:00 pm »

ah. I think the heaters for 4 6SN7s need to be 6.3v @4.5A at least.

BillB · « **Reply #8 on:** 12 Dec 2008, 02:06 am »

Maybe run 24v and run the heaters in series, then you can get away with the single valve's current rating.

sts9fan · « **Reply #9 on:** 12 Dec 2008, 12:57 pm »

Am correct that when using a center tapped transformer the voltage is doubled?

BillB · « **Reply #10 on:** 12 Dec 2008, 05:46 pm »

Not if you rectify as such:

tap one----diode---------

center tap----ground

tap two----diode--------^ (to tap one)

sts9fan · « **Reply #11 on:** 12 Dec 2008, 05:54 pm »

This is what I will be doing

I know I want ~400-500 vdc.

BillB · « **Reply #12 on:** 12 Dec 2008, 06:55 pm »

Have you downloaded Duncan's PSUD?

http://www.duncanamps.com/psud2/index.html

That should ballpark you.

JoshK · « **Reply #13 on:** 15 Dec 2008, 03:10 pm »

For 6SN7's you want 300-325V....400+ is too high. You'll likely exceed the maximun voltage ratings on some 6SN7's if you run at >400vdc.

I suggest reading the aikido manual very carefully and download the janus manual and read that carefully too. Everything you need to know is in these.

Josh

sts9fan · « **Reply #14 on:** 15 Dec 2008, 06:32 pm »

Thanks Josh I realize what the voltage should be. I am using a Janus regulator so I am looking for ~350vdc pre regulator. I have read everything quite a few times and 350 pre reg is taken direct from tubeCAD journal. I am mostly unfamiliar with CT transformers but I think I have a handle on that now.
Thanks for your input
Kris

sts9fan · « **Reply #15 on:** 15 Dec 2008, 06:43 pm »

Please let me know if this is incorrect

500VCT/1.43 - 2 = 347.65vac > regulator > ~300vac

Is this the wrong calculation for this application?

JoshK · « **Reply #16 on:** 15 Dec 2008, 07:07 pm »

Hmm...oddly you get to the right answer, but the wrong algebra.

I am assuming you are planning to use a full wave rectifier (not bridge) and solid state diodes rather than a vacuum rectifier. If that is correct, then the math is more like this (approximation):

500VCT is 250/0/-250 vac => 250vac * 1.43 - 1.2v = 356vdc. I am pulling the diode drop off the top of my head. I can't recall if this is right, but as you can see it has very little impact. If vacuum tubes are to be used the diode drop is much larger, like 25v for damper diodes to 50+V for regular VT rectifiers.

P.S. this also assumes that this is a cap input filter where the first cap is relatively large. For choke input filters, the multiplying factor is roughly 0.9 instead of 1.43. You get less voltage but better regulations and ripple waveform with a choke input filter.

note: nevermind...I see that broskie made the formula simpler for folks. 500vct/sqrt(2) = 500vct/2*sqrt(2). So yeah, your math is correct, just not the way I think about it.

sts9fan · « **Reply #17 on:** 15 Dec 2008, 08:07 pm »

please refer to page 13 of the Janus pdf.
http://www.tubecad.com/Product_PDFs/Janus%20Rev%20A.pdf

I was using the FW CT equation. Can you tell me why that is incorrect? Also it is tube rectified.

edit: never mind I get it.

Thanks for your help
Kris

sts9fan · « **Reply #18 on:** 15 Dec 2008, 08:17 pm »

Can you explain or point me to info on Damper Diodes vs VT rectifiers?

Thanks
Kris

JoshK · « **Reply #19 on:** 16 Dec 2008, 12:13 am »

OK, so I looked up that Broskie supplies the Janus kit with a Sovtek 5y3gt. The 5Y3GT drops 50V @ 125ma. Let's assume that 50V is close enough. Then the math works like this.

XXX vct = XXX vac/2 * 1.414 - 50V = 350vdc desired, solve for XXX

XXX = (350+50)/1.414*2 = 565vct, in reality 550vct is close enough since you probably arent pulling 125ma from this supply, which means the voltage drop is less than 50V.

Broskie recommends the inexpensive Allied transformer, but the filament current isn't sufficient to run an all 6sn7 aikido. You can get a somewhat larger Hammond, or add a seperate filament transformer. Probably equal costs. I like the seperate filament solution myself as it has a few advantages in terms of lessening the tax on the power tranformer core and noise decoupling. It requires more space though.