2a3/45 transformer wiring

2nd harmonics for the masses

2a3/45 transformer wiring

Postby jetpack » Sat Nov 01, 2014 3:56 pm

Hi all.
I'm resurrecting an old battle-scarred GSG board into life as a new 45 amp. I have a couple of questions about wiring my power transformer. Any chance somebody would take a look over this wiring attachment and let me know if I'm on the right track with the heaters?
Thanks!
gsg45wiring.pdf
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Re: 2a3/45 transformer wiring

Postby jetpack » Sat Nov 01, 2014 11:07 pm

So I left the workshop, left the house, and thought about it. I decided to try using one 6.3V 3A secondary for the 6sl7, a 3A 5V secondary for the 5R4, and separate 2.5V taps for each 45. At least the filaments light up. I've also got the high-voltage centre tap going to J4P2. If I get it making sound, I'll try to post a picture.

As an aside, I've been running a 6A3 GSG to a pair of Fostex 206en and it sounds great.

Cheers.
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Re: 2a3/45 transformer wiring

Postby Shannon Parks » Mon Nov 03, 2014 10:23 am

Jetpack, I'm a little bit lost on your posted diagram. What PT are you using? Are you following these docs:
viewtopic.php?f=14&t=5499

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Re: 2a3/45 transformer wiring

Postby jetpack » Wed Nov 05, 2014 1:25 pm

Yes, I'm following the 2A3 and 45 docs. The power supply is working fine now. The heaters have a little over 5V (5R4-GY), 6.3V (6SL7), and 2.5V (45), all AC. The B+ without the output tubes in is 353V. I guess this is way too high for type 45. I have a spare 5H choke that I might add to the 1.5H one already in. I'm also using a 5R4-GY which should (according to http://www.fourwater.com/files/fullrect.txt) drop 67V. Even with this, maybe the B+ will still be too much. Any thoughts on how I should proceed? Thanks!
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Re: 2a3/45 transformer wiring

Postby jetpack » Wed Nov 05, 2014 1:27 pm

gsg45.jpg
gsg45.jpg (313.17 KiB) Viewed 1714 times


and a photo:
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Re: 2a3/45 transformer wiring

Postby Shannon Parks » Thu Nov 06, 2014 11:56 am

jetpack wrote:Yes, I'm following the 2A3 and 45 docs. The power supply is working fine now. The heaters have a little over 5V (5R4-GY), 6.3V (6SL7), and 2.5V (45), all AC. The B+ without the output tubes in is 353V. I guess this is way too high for type 45. I have a spare 5H choke that I might add to the 1.5H one already in. I'm also using a 5R4-GY which should (according to http://www.fourwater.com/files/fullrect.txt) drop 67V. Even with this, maybe the B+ will still be too much. Any thoughts on how I should proceed? Thanks!


Without the output tubes, your power supply isn't loaded so there won't be any sag from all the DC resistances. Go ahead and use a Variac if you have one, but I think you'll be fine if you don't. For old stock 45s, I'd shoot for 275V with the cathode voltage drop. I bet you're below that. Just be sure to do a quick calc of your plate dissipation after fire up.

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