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pjanda1 12th August 2009 04:40 PM

Series wire Antek Secondaries
 
I just received an Antek 4T400. I wired the two 400V secondaries in series to get 800VCT (taking the B+ off the CT), and it worked perfectly well: dead quiet (which is why I'm using it to replace a NOS Stancor). I'm getting slightly higher losses in the PS than I had hoped, so I'd like to get a little higher voltage. Is there any reason I can't wire both the 6.3V windings in series as well? To keep the CT in the center, I would wire the 6.3, 400, 400 and 6.3 secondaries in series in that order. I'm assuming it is just fine, but there is a great deal I do not know about transformers. After some searching, I still figured I oughtta' ask.

pj
www.wildburroaudio.com
affordable, US made fullrange loudspeaker drivers

tomchr 12th August 2009 05:54 PM

I would be a little concerned with the breakdown of the isolation between the two 6.3 V windings. But that could be fixed by changing the wiring to: 400 V - 6.3 V - CT - 6.3 V - 400 V. I don't know if that's possible with that transformer.

I think the wiring you propose will probably work. To be sure, you could toss Antek an email and ask if the two 6.3 V windings may be 800 V apart.

But are you really so pressed for voltage that a 1.6 % increase will break or make the day? If that's the case, you'll really need a transformer with higher output voltage (or lower losses in the power supply) as the AC line voltage will vary by more than that over the course of a day.

~Tom

Poindexter 12th August 2009 06:32 PM

Why don't you ask John?  If he doesn't know, he'll ask the actual winding engineers and report back, and then you won't have to rely on information from a bunch of people like me, who may or may not know the score.  Web fora are a notoriously unreliable place to pick up this sort of information.

Aloha,

Poinz
AudioTropic

pjanda1 12th August 2009 06:40 PM

I asked John (in two separate emails) if I could connect the 400V windings in series, and he never responded. So, while I haven't asked this specific question, I figured I'd have better luck here. I know the voltage increase is small (wouldn't it be more like 3%?), but I'm not using the windings and a little higher B+ would be nice. It's not that I can't get by fine without it, but why not use the whole thing if I can?

pj

tubelab.com 12th August 2009 07:17 PM

Quote:

I asked John (in two separate emails) if I could connect the 400V windings in series, and he never responded.
Connecting the two 400 volt windings in series to make an 800 VCT winding is OK. This fact is stated in the text in many of his Ebay auctions for these transformers. I copied this from the auction for a bigger transformer.

"outputs 500Vac x 2 (dual coils can be connected in series for 1000Vac center tap or parallel for extra current for 500V at 700mA)"

I have used a 4T400 as an 800 VCT transformer in a Simple SE amp. My problem was too much voltage I was getting about 540 volts of B+ which can make the 500 volt electrolytics very unhappy. I have a 4TK400 transformer that is similar but has 70 volt taps. It is wired in the usual manner as an 800 VCT secondary with the center tap grounded. it works good too.

If you needed to add the 6.3 volt windings, I would wire them like tomchr states since the two 6.3 volt windings are wound on the same layer with no extra insulation between them.

Matt BH 12th August 2009 09:22 PM

Just caught this thread, Tubelab and Tomchr have said what I would have said.

I have a couple of 4T360 trannys from Antec. Try it by all means but if there is a fault in the rectifiers it could put a lot of voltage between the 6.3V windings and chassis, so be sure the CT is connected to chassis and not floating, use the rubber washer aswell.

What rectifiers are you using if SS can you not use slightly bigger caps to gain the exta couple of percent increase? or try some rectifiers with a lower forward drop.

I just re-read your OP. What do you mean by taking the B+ from the CT?

Cheers Matt.

pjanda1 13th August 2009 12:37 AM

Matt,

The bridge is what Eli Duttman calls a cockeyed bridge. I'm using a choke input supply, but I do have a tiny cap in front of the choke (.1 or .22). I've tried raising it's value a little with past power transformers, and it hasn't changed the voltage much. I don't want to end up with a cap input supply with a tiny first cap.

If this is a poor/risky idea, I'd be happy to abandon it. I just feel compelled to wring every last bit out of the parts I've got. FWIW, the transformer will be fully enclosed in a steel chassis that is well grounded.

pj

tubelab.com 13th August 2009 12:55 AM

Cockeyed or not, it is electrically similar to the standard full wave CT circuit that has been used in tube amps for years. The ground connection has been moved, and D5 seems redundant. Your 6.3 volt idea will work here, just put the 6.3 volt windings in the center (so they are connected to D5). This way they operate with a low voltage between them.

I was getting 540 volts out of my Antek using the standard full wave CT circuit with a 200 mA load. Adding the 6.3volt trick should net you about 8 more volts.

You could rewire the whole thing to resemble a FWCT circuit, put the two 6.3 volt windings in series and wire them to a conventional bridge rectifier with a good sized cap across them to make a 16 volt supply. Ground the negative output from the 16 volt supply and connect the CT of the 800 volt winding to the positive end of the 16 volt supply. Now you have a 16 volt supply and a 540 volt supply in series, for 556 volts.

Tom Bavis 13th August 2009 01:14 AM

For that matter, you could use the 2X 6.3V windings into a doubler (about 30V) or tripler (45V) and connect THAT in series...

pjanda1 20th August 2009 03:17 PM

I did ultimately contact John and he said it would be fine. It is wired up and working great!

thanks,

pj


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