Power transformer options

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Power transformer options

Postby Ty_Bower » Sat Aug 06, 2011 7:33 am

I mentioned in the first post that I was thinking about two power transformers from Edcor:

Ty_Bower wrote:XPWR165-120/240 $32.46
Power transformer for a 120V or 240V, 50/60Hz. line to 400V (200-0-200) at 50mA center tapped and 12.6V at 2.5A.

XPWR177-0/120/220 $39.53
Power transformer for a 120V and 220V, 50/60Hz. line to 400V at 70mA center tapped and 6.3V at 2.5A center tapped.


Thinking about a 1626 build... If I go with the first, I guess I just put jumpers in the right places and feed AC straight to the heaters? Does anyone see this as a problem? I suppose I should go look at the datasheet for the 1626 and see what they say. Oh, I see. It's an indirectly heated tube. I don't know why I thought it was directly heated.

Of course, if I use the second transformer I might have easier options if I ever want to try tubes with 6 volt heaters. Two and a half amps should be enough to light up a pair of 6L6G, or more than enough for a pair of 6V6GT.

If anyone wants to chime in with ideas for the 6L6GC option, don't be shy. Is half a 'SL7 really going to have enough drive for a 6L6GC?
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Re: Power transformer options

Postby Shannon Parks » Sat Aug 06, 2011 11:41 am

Ty_Bower wrote:Is half a 'SL7 really going to have enough drive for a 6L6GC?


My numbers with the previously mentioned Edcors, a PA774 at 400V and a Russian 6L6 in a GSG Clementine mockup:

20Hz to 20kHz -1dB bandwidth with no feedback
12Hz to 31kHz -1dB bandwidth with 3dB global negative feedback
<10Hz to 48kHz -1dB bandwidth with 6dB global negative feedback

I did allow for a negative feedback mod in the Clementine to help compensate for these budget SE transformers and to fortify the 'SL7 driver. But even without feedback, we are getting acceptable high frequency response in spite of the Miller Effect issue due to the high gain and higher output impedance of the 'SL7.

Interesting thought: can I use 6dB feedback and then drive parallel SE? Maybe.

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Postby Ty_Bower » Sun Aug 07, 2011 1:10 pm

I'm also wondering if the Antec toroid might work here...

http://www.antekinc.com/details.php?p=46

AN-1T200 $29
two windings, 200 volt @ 0.22 amp
two windings, 6.3 volt @ 3 amp
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Postby TerrySmith » Sun Aug 07, 2011 1:34 pm

I was wondering the same thing except using the AN-05T200. Either should work fine?
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Postby EWBrown » Sun Aug 07, 2011 1:58 pm

I've used the Antek AN-05T200 in a 12B4A SET design, which has all the same electrical parameters, and the resistance values as the Clementine 1626 circuit (just different tubes, 12DT8 and 12B4As). Works just fine, and the amp is dead quiet, no hum, ripple, buzz or other PSU related noise gremlins.

It has plenty of available B+ current, a pair of 1626s or 12B4As consumes lsss than half of its available B+ current, and since it has two 6.3V 2A filament windings, just connect thenm in series and use 12V AC (or rectified to DC) for the filaments. The trannie could easily feed two 1626 Clementines, for four channel SET, two channel PSET, or stereo "floating paraphase" PP. [:) [:) [:)

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Postby Ty_Bower » Sun Aug 07, 2011 3:47 pm

TerrySmith wrote:I was wondering the same thing except using the AN-05T200.


I looked at it, but the Antec specs seem to indicate it only has a single HV secondary winding. I guess you'd need to use a FWB rectifier, and the Clementine board isn't really set up for that. I suppose you could do it with a little fiddling...
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Postby EWBrown » Mon Aug 08, 2011 9:28 am

That is correct about the AN-05T200, the HV winding is tapped at 180VAC and 200 VAC, with no center tap. So, it does require the use of a four diode FWB.

Easiest way to implement this would be to mount two rectifiers conventionally on the board, then add two more, cathodes connected to the HV secondary winding, and the anodes, tied together, connect to ground. For neatness, the two "positive" diodes could mount on the tube socket side of teh board, and the two "negative" rectifiers, on the solder side, just use enough lead length so that they will clear any other board mounted components, and this can be done neatly and cleanly - I've done this on various other PC board projects, with excellent results.

The alternate method would be to use a 5 point (center lug ground, which is not necessary to use) and mount the four rectifiers into a bridge configuration, on that, connect the HV AC from the PT to the two cathode/anode junctions, and then connect the CD from the bridge to the PC board, this may be easier for some folks and also can be done neatly and cleanly.

Third method, probably the least desirable, is to get a packaged 1000 PIV 1A bridge, and connect it in the usual way. The "undesirability" is that it may be not so easy to procure a packaged bridge made with ultrafast diodes like the UF4007.

Lastly, and I dare say, leastly ;)

There are those cute little "DF08" packaged bridges, packaged as a 4 pin DIP IC, which is the same dimensions as an 8 pin DIP.

I've used them, but I really don't trust them for having a long life at much more than 100 mA max, even though they are 1A rated. :/ :|

To use them, I use a small piece of perfboard, and mount the bridge and the first electrolytic cap, and a 270K, 1W bleeder resistor on the board, and then feed the DC voltage to the circuit.

They are can be a real pain in the butt, to try to mount on a PCB which doesn't have the proper pad layout to mount them (666)

HTH

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Postby Shannon Parks » Mon Aug 08, 2011 6:31 pm

EWBrown wrote:Third method, probably the least desirable, is to get a packaged 1000 PIV 1A bridge, and connect it in the usual way. The "undesirability" is that it may be not so easy to procure a packaged bridge made with ultrafast diodes like the UF4007.


This is a monster bridge rectifier from a power supply, but it gives you an idea.

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Postby EWBrown » Tue Aug 09, 2011 11:25 am

If that "monster" can fit, on the board then it should be "duck soup" to install a smaller sized one, 1 or 2A, 1000 PIV ;) (lol)

That also allows using a cheap, small isolation / step-up transformer for generating the B+, whether toriod or open-framed, along with a 12VAC filament trannie.

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Postby TerrySmith » Fri Aug 19, 2011 10:40 am

I was really wanting to use the Antek toroid but they won't have the cover available for two months. So it's looking like either of the two mentioned Edcors or the Hammond like Tom uses.

What is the B+ current draw on a Darling / Clementine?
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Postby TomMcNally » Fri Aug 19, 2011 10:53 am

Terry -

I've built 20 some point to point Darlings with the Hammond
269EX (now with 125 volt primary) or 369EX for 120/240,
and the voltage doubler for the filaments. I like the quietness
of DC on the fils ... and the Clementine board makes that
soooo easy to wire up. I've used toroids for 13EM7 amps,
in fact, I'm listening to one here in the office at work right now.

I like hiding the ugly stuff under the chassis.

... tom
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Postby Shannon Parks » Fri Aug 19, 2011 11:14 am

TerrySmith wrote:I was really wanting to use the Antek toroid but they won't have the cover available for two months. So it's looking like either of the two mentioned Edcors or the Hammond like Tom uses.

What is the B+ current draw on a Darling / Clementine?


Darling is 50mA and the Clementine 6L6 is around 100mA. I think. Tom, could you post your bias voltage for your Chubby?

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Postby TerrySmith » Tue Aug 23, 2011 9:47 am

I ordered my transformers yesterday, ended up going with the XPWR177-0/120/220 power and GXSE10-8-5K outputs. The PT is rated 400-0-400 @70ma and 6.3v @ 2.5a, 50 - 60hz.

Do I have enough filament current for maybe a tube rectifier, possibly a 6X5? I would wire it to the rect first and then to the PCB.

I've also thought of a custom power transformer for the next clementine/darling, maybe 400-0-400 @ 75ma, 6.3v @ 3.5a? Maybe we can all collaborate and come up with the perfect Darling transformer! I won't mind paying or splitting the setup fee.
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Postby TomMcNally » Tue Aug 23, 2011 6:12 pm

separks wrote: Tom, could you post your bias voltage for your Chubby?
Shannon


Here are some voltages taken under 8 ohm loaded output,
shorted input ...

at diodes before warmup - 463
after warmup - 423

at primary of OPTs - 407 (across C9)
at plates of 6L6's - 400
at C-10 (decoupler for 6SL7) - 373

at cathodes of 6L6's ... 32.5 / 30.8 (tubes not matched)
plate to cathode of 6L6's ... 370 / 369

plates of 6SL7 ... 212
cathodes of 6SL7's ... 1.75
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Postby Ty_Bower » Tue Aug 23, 2011 8:11 pm

TerrySmith wrote:I ordered my transformers yesterday, ended up going with the XPWR177-0/120/220 power and GXSE10-8-5K outputs. The PT is rated 400-0-400 @70ma and 6.3v @ 2.5a, 50 - 60hz.

Terry, I think you missed a crucial spec on that PT. I ordered the same for my 1626 build. Edcor's page says it is 400VCT, or 200-0-200. For both our sakes, I hope I'm right. If it really is 800VCT as you wrote, we're going to need to find some caps with a heckuva voltage rating.

TomMcNally wrote:Here are some voltages taken under 8 ohm loaded output...

Tom, you forgot to mention you are using an XPWR005 in that particular build. It's essentially a clone of the PA774 power transformer used in the Stereo 35. Those voltages look like they are a pretty good match for 6L6 flavored tubes. Less voltage, and performance is going to suffer a little. More voltage, and you'll need 500V rated caps, which are a pain to find. On a side note, that XPWR005 also works perfectly in a GSG.

Image
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