different power tranny? R-Core?

a 3W single ended EL84 amp for home, work & school

different power tranny? R-Core?

Postby kmbois » Tue Jan 22, 2013 5:31 pm

Has anyone tried an R-core Transformer in the Budgie? I was also wondering about other parts substitutions before I start soldering. Also does anyone have an digital copy of the instructions/parts list?
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Re: different power tranny? R-Core?

Postby Shannon Parks » Tue Jan 22, 2013 6:54 pm

Doc link:
viewtopic.php?f=21&t=5563
The Budgie SE is still pretty new, with just a few out there right now. I'm enjoying mine as I type this. The PCB will certainly work with a variety of power trannies, though the top plate is designed for a couple Edcors. Did you have a link for one in mind?

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Re: different power tranny? R-Core?

Postby kmbois » Thu Jan 24, 2013 6:45 am

There are 2 on ebay. The first one which is 250v-0-250v the other 265v-0-265v. The first I can't order until Feb. 15th
I have some Chinese R-Cores in my DACs and the DACs sound beautiful.

http://www.ebay.com/itm/110752425410?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
http://www.ebay.com/itm/220946913915

I have a pair of old Telefunken Output Transformers that I plan to use. I also want to use some better caps and resistors at least in the signal path.
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Re: different power tranny? R-Core?

Postby Ty_Bower » Thu Jan 24, 2013 7:19 pm

The second one you linked specs two high voltage windings, each 0-265 VAC at 20 mA. That's not what you want.

The other says 500 VCT (250-0-250) at 75 mA. That should work fine, but at $43 plus $28 shipping the Edcor is a lot cheaper.

I've been using the Nichicon audio grade caps (KZ series) for stuff like cathode bypasses, and Wima MKP for coupling. I can't say if it makes an audible difference, but the caps only cost a few cents more. I'll put carbon composition resistors in grid stopper locations, but I prefer to stick with the precision metal film parts (Dale) for most everything else ('cept anything that needs to dissipate a lot of power).

All that said, if you stick to the stock bill of material, it will come out sounding very good. [:)
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Re: different power tranny? R-Core?

Postby kmbois » Wed Feb 06, 2013 5:11 pm

Thanks for the advice.
i will order the Edcor, I think. I will be using Janzten Caps for the coupling caps.
I can't seem to find R22, R23 on the schematic or parts list, but they are there on the PCB. Any idea what those values are?
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Re: different power tranny? R-Core?

Postby soundbrigade » Thu Feb 07, 2013 10:25 am

I think I have two R-cores lying around. One is aimed for a 6AQ5-SE (miniature amp) and the other if I have a second one is ... unknown.
Source: http://www.vt4c.com/shop/program/main.php?cat_id=55&group_id=7
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Re: different power tranny? R-Core?

Postby EWBrown » Thu Feb 07, 2013 10:17 pm

Tube Depot had these R-Core power trannies on sale (USD $39.95) last month, so I bought two for experimental fodder..

http://tubedepot.com/tr-pw-879s.html

As produced, these have a 100 VAC primary, and 260VAC @ 150 mA, and 6.3VAC @ 3A secondaries.

These can be run with 120VAC on the primary, and the secondaries will then be 312 VAC, and 7.56 VAC, under rted current loading.

For my test, I fed the primary with 100VAC from a Variac, with the 260VAC winding loaded with a 40W, 230V Philips ligght bulb (approx 180 mA load at 260V),
and a 6080 (2.5A load) on the 6.3VAC winding, and ran it for several hours,. The R-coe transformer just barely got warm, so I would presume
that it could handle even heavier current loading, by at least 20%.

I have an idea for a good application for these trannies, and that is an 8BQ5 / 8CG7 stereo SE amp. With 120VAC on the primary,
the lightly loaded filament winding would deliver fairly close to 8VAC, and the HV secondary, at 312 VAC could then be FWB rectified,
with a CLCRC filter string, which would deliver around 360VDC for the power stages, and 300-325VDC for the driver stage, which could be either a standard
grounded cathode, or with an extra tube, SRPP drivers. (I've used 6CG7 SRPPs, driving EL84s and 6GK6s with very good results).

Such a circuit would consume approx 80-85 mA B+ current, and either 1.65 or 2.1A filament current, which are well below the winding's 3A rating.

These power trannies were originally designed for this Japanese stereo 6L6GC SEP amp kit, http://tubedepot.com/diy-ek-tu-879s.html
so the lesser-powered 8BQ5 design would be a relatively lightand easy load for the PSU.

I don't know of an 8V filament version of a 12AX7A, otherwise this would work nicely with the Budgie SE circuit board (though not fit on the Budgie's top plate.
8CG7s would not have sufficient voltage gain for proper operation with the NFB loop, but are OK if no NFB were used.

The Russian 6N2P which is essentially a 6AX7, could be used with a 5 to 6 ohm, 2W dropping resistor in series with the filament.

/ed B
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