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PostPosted: Tue Oct 19, 2010 8:14 am
by Ty_Bower
EWBrown wrote:The 6.3VAC filament windings... CANNOT be paralleled with the HV and bias windings.

The "extra" filament windings could be series connected with the HV winding if you needed 6 or 12VAC above the HV winding's AC voltage.


Ed, I was planning to take the yellow secondary winding and connect it in series with the primary. If I phase it correctly, this should lower all three of the remaining secondaries (red, green and blue) a little bit.

Most of the line voltage will still be divided across the primary, so I do not believe I'm going to overvolt the yellow winding. The yellow winding certainly has enough wire gauge in it to handle the current - in fact I'd expect the yellow's current handling capability is far greater than the primary's. The only safety question remaining is whether all the secondaries are sufficiently insulated from each other. I wouldn't want to put line voltage on one of the secondaries, then have an insulation breakdown. I'm assuming that all windings are sufficiently insulated. After all, one of the windings has "high voltage" on it.

PostPosted: Tue Oct 19, 2010 8:43 am
by dcriner
With the dual primaries, it could be used as an isolation xfmr for the bench.

PostPosted: Tue Oct 19, 2010 10:23 am
by EWBrown
I've used the "extra filament winding" buck / boost technique before, it works quite well. Good use for that unused 5VAC rectifier winding in an SS rectified PSU.

Since the AC voltages are relatively low (170VAC max) and you are not using it in a voltage doubler, there should be no insulation breakdown issues to wory about. These trannies are (or at least should be) hi-potted to 1500VAC / 2121 VDC minimum) for product safety compliance,
to ensure that primary to secondary insulation is sufficient and safe.

In the stereo 6BM8, this trannie is gonna be SERIOUS overkill, no B+ sag to worry about... I'd use hefty rectifiers, like 1N5408, uF5408 or some HEXFREDs, just to be safe, especially if you plan on using big PSU caps.

/ed B

PostPosted: Tue Oct 19, 2010 10:52 am
by Ty_Bower
EWBrown wrote:I've used the "extra filament winding" buck / boost technique before, it works quite well.

Since the AC voltages are relatively low (170VAC max) and you are not using it in a voltage doubler, there should be no insulation breakdown issues to worry about. These trannies are (or at least should be) hi-potted to 1500VAC / 2121 VDC minimum) for product safety compliance.

Good to know. I think I've figured the HV is going to get lowered to ~166.5 VAC, which should give me a final B+ of 222 VDC. The heater winding should come down to 6.6 VAC, which is close enough for me.

In the stereo 6BM8, this trannie is gonna be SERIOUS overkill, no B+ sag to worry about... I'd use hefty rectifiers, like 1N5408, uF5408 or some HEXFREDs, just to be safe

I'm expecting nothing less than serious overkill. (666) I'm wondering how much capacitance I can stuff under the chassis.

Somewhere around here I've got a pile of bridge rectifiers salvaged from old PC power supplies. I searched up the datasheet for one labeled RS405L. It can handle a PIV of 600 volts, which is plenty for this application. It's good for 4 amps continuous, or 150 amps peak on a single half sine. They do warn to de-rate the current by 20% if the load is capacitive, but I think I'll still be OK. Pity they don't show the switching time. It might make sense to put something fast in series after the bridge.

PostPosted: Tue Oct 19, 2010 10:57 am
by EWBrown
I've used those bridges salvaged of f computer SMPS for 230VAC or lower applications, with good results. They already can handle 120VAC as a doubler, or 230VAC as a FWB, and I've never had any problems using them along with BIG electrolytics (also salvaged from the same type of SMPS.

My favorites are the 1000 uF / 200V and 470 uF / 400V, these can make for a super heavy duty PSU, use the 200V units in series, or for the first caps in a doubler. I spent many a lunch hour on the last job, rescuing useful parts from "dead" switcher PSUs which were getting tossed out in the recycle boxes, and I now have nearly a lifetime supply of these parts - even in the unlikely event that I were to make it to 150 years old ;) (lol)

/ed B

PostPosted: Tue Oct 19, 2010 12:49 pm
by DeathRex
He says he loaded it with 200ma and got 606 volts, so is the transformer rated 235volts at 500-560ma?

PostPosted: Tue Oct 19, 2010 1:41 pm
by elbinster
Also mega overkill for my future 8x2 mixer (currently in the pipe-dream design phase). But that 44V winding would make for a very convenient phantom power supply.

PostPosted: Thu Oct 21, 2010 3:02 pm
by EWBrown
He says he loaded it with 200ma and got 606 volts, so is the transformer rated 235volts at 500-560ma?



In full-wave voltage doubler service, the trannie's AC current must be 2.8 to 3.6X the DC output current, so these trannies are good for at least 560 mA @ 230VAC, and most likely 720 mA or greater. I already started some AC loading tests. Unloaded voltage is 235 VAC, most likely 225 to 230VAC under full rated current loading.

My trannies arrived yesterday (Wednesday, Oct 20), I set one up on the bench, loaded the red-wires HV (230V) winding with two 40 watt / 230 V light bulbs, and the "green" filament winding with four 6AV5GAs, for a 5 amp load. Ran it for a few hours, the trannie barely got warm. I have four of these bulbs, and if I need to absorb more current, then I can connect appropriate wattage 120VAC bulbs in series / parallel , to handle 230VAC.

I haven't yet load tested the yellow and orange 6.3V filament windings, but I SWAG these are good for at least 3 A each.

No load voltage was 235 VAC, one 40W bulb was 233VAC, and with two 40W bulbs, 231 VAC on the "red" winding. That's about 350 mA AC loading. I need to get 1 or 2 more ceramic bulb sockets to load it up for more current.

These trannies are monsters, big and heavy, and could easily handle a 120W amp, with plenty of VA to spare.

I'm sure that the mail-marm had a few "choice" words while she was handling the box, probably about the heaviest "flat rate "11 X 8.5X 5 box she has seen... A thrid trannie couild fit, but it would be a real tight fit...

These are packed in their own close-fitting corrugated cardboard boxes, and he had to use heavy big steel staples to make sure that the FR box didn't burst open in transit.

/ed B

PostPosted: Thu Oct 21, 2010 3:24 pm
by mesherm
Speaking of cheap iron on e-place...
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=400165688077&ssPageName=STRK:MEWNX:IT

I bought two. For $6.99 each and cheap shipping I can take a chance.

PostPosted: Thu Oct 21, 2010 5:33 pm
by Shannon Parks
mesherm wrote:Speaking of cheap iron on e-place...
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=400165688077&ssPageName=STRK:MEWNX:IT

I bought two. For $6.99 each and cheap shipping I can take a chance.


Company link, but less info:
http://www.specotechnologies.com/cart/p ... prodID=157

--Shannon

PostPosted: Thu Oct 21, 2010 6:46 pm
by Ty_Bower
I thought those Speco's had no gap. Are they really suitable for single-ended use?

PostPosted: Thu Oct 21, 2010 7:22 pm
by mesherm
I plan to use them in a small dirt cheap 6S4A PP amp so air gap is not a factor. ;)

PostPosted: Thu Oct 21, 2010 7:42 pm
by Ty_Bower
Since when do you do PP, Mike? I thought you quit that a while ago... ;)

PostPosted: Thu Oct 21, 2010 11:20 pm
by mesherm
Since when do you do PP, Mike? I thought you quit that a while ago...


I built a small cheap PSE amp using 6S4As a while back and while it had about 4 watts of power the bass below about 200 hz was poor and the sine wave distorted the lower the frequency got.
One of my long standing projects was to convert it to PP but I didn't want to invest much money.
I'm going to swap out the small SE OTs for the cheap PP OTs and do a bit of circuit rewiring and see if I can improve the amp enough to possibly sell it. (y) $)

PostPosted: Fri Oct 22, 2010 3:29 am
by Geek
Please let us know how those do.... 2.5" mounting centres I can't see going to 30Hz, let alone 20Hz at all over maybe a watt (???)

Cheers!