I was planning on building an SE EL84 amp, and I'll probably still do so, but while I wait for Edcor to ship me their iron, I was wondering what other possibilities I might consider. I'm just fishing for interesting possibilities.
The Edcors will be a pair of CXSE25-5K (6-ohm version for my 97dB Omegas) and an XPWR007 (275-0-275). I'm committed to the OPTs, but I'm open to buying a bigger power transformer if need be.
I'm listening to either an F4 SS amp or a Chinese SE EL84 right now. I used to own a 6B4G SET amp from Shannon Parks' site that I built (PCB-based). Preamp is Wayne's BA2018 line stage or an LTA MZ2. The Chinese amp sounds surprisingly good, so I'm of two minds now: build a better EL84 amp or build something completely different?
The Edcors will be a pair of CXSE25-5K (6-ohm version for my 97dB Omegas) and an XPWR007 (275-0-275). I'm committed to the OPTs, but I'm open to buying a bigger power transformer if need be.
I'm listening to either an F4 SS amp or a Chinese SE EL84 right now. I used to own a 6B4G SET amp from Shannon Parks' site that I built (PCB-based). Preamp is Wayne's BA2018 line stage or an LTA MZ2. The Chinese amp sounds surprisingly good, so I'm of two minds now: build a better EL84 amp or build something completely different?
A Tubelab SSE would work nicely with those outputs.
An XPWR134 will give you many options for the output tubes & rectifier.
An XPWR134 will give you many options for the output tubes & rectifier.
Hmm, lots of happy Tubelab SSE builders, so that's worth keeping in mind. I have a Tom McNally-built Darling 1626 amp which I like. It looks like a parallel version is possible with what I have?
Post # 4 . . .
I could not find a complete 5881WXT data sheet.
I hope its maximum screen voltage is rated higher than a 5881 maximum screen voltage.
5881 (non-WXT)
I hope the Screen always draws enough current to keep D1 in its true Zener region.
Otherwise we will have a discontinuity, with the sonic implications, possible distortion,
possible transient "kicks".
And when the plate swings down to 50V, it will be drawing Lots of screen current.
I hope the zener takes that much current.
And, the screen voltage will be at 320V, but the 5881's screen is only rated for 270V.
It will probably always be drawing screen current, since it always is 50V higher than the 5881 screen' maximum voltage rating.
I could not find a complete 5881WXT data sheet.
I hope its maximum screen voltage is rated higher than a 5881 maximum screen voltage.
5881 (non-WXT)
I hope the Screen always draws enough current to keep D1 in its true Zener region.
Otherwise we will have a discontinuity, with the sonic implications, possible distortion,
possible transient "kicks".
And when the plate swings down to 50V, it will be drawing Lots of screen current.
I hope the zener takes that much current.
And, the screen voltage will be at 320V, but the 5881's screen is only rated for 270V.
It will probably always be drawing screen current, since it always is 50V higher than the 5881 screen' maximum voltage rating.
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EL84 Single Ended:
The Edcor CXSE25-5K has a 40% screen tap.
An EL84 optimum UL tap is somewhere between 20 to 33%.
40% will be closer to Triode wired mode.
Try the 40% tap.
And try the 100% tap (Triode wired).
Those are easy things to try.
Be sure about the B+ voltage you use, versus the EL84's voltage ratings.
They can do more than those ratings, but do so at your own risk.
Your Mileage May Vary.
The Edcor CXSE25-5K has a 40% screen tap.
An EL84 optimum UL tap is somewhere between 20 to 33%.
40% will be closer to Triode wired mode.
Try the 40% tap.
And try the 100% tap (Triode wired).
Those are easy things to try.
Be sure about the B+ voltage you use, versus the EL84's voltage ratings.
They can do more than those ratings, but do so at your own risk.
Your Mileage May Vary.
Thanks, everybody! I think I'll try out multiple configurations since I have most of the components on hand already, at least I will whenever the Edcors show up. You guys made me realize I can just play around and experiment, which is obviously the most educational and fun way to proceed anyway. I still need to better understand what's in the pages of my copy of Morgan Jones' book, too.
You have a very large number of tubes that will work with that transformer.
Pick your favorite tube, according to looks, cost, size, etc.
I have used single ended 5k output transformers with 2A3, 300B, 6L6GC, 807,
7591, KT77, KT66, EL34, and I can not remember if there were others too.
5k is not optimum for some of those tubes, depending on what parameters you want to be optimum . . .
output power, distortion, frequency response, damping factor, etc.;
And what kind of operating mode . . . Pentode/Beam Power, Ultra Linear, Triode mode.
Then, there is No negative feedback, Schade negative feedback, and Global negative feedback.
Many of the possibilities are limited, by things like the power transformer:
filament current enough to run the chosen tubes
B+ voltage.
A Cap input filter can give B+ about 1.4X the RMS voltage.
A Choke input filter can give B+ about 0.9X the RMS voltage.
A Modified Choke input filter with a very small input cap can give a B+ voltage that is in-between 0.9X and 1.4X.
Lots of things to try, but pick one or two to start.
Enjoy building.
Enjoy listening!
Pick your favorite tube, according to looks, cost, size, etc.
I have used single ended 5k output transformers with 2A3, 300B, 6L6GC, 807,
7591, KT77, KT66, EL34, and I can not remember if there were others too.
5k is not optimum for some of those tubes, depending on what parameters you want to be optimum . . .
output power, distortion, frequency response, damping factor, etc.;
And what kind of operating mode . . . Pentode/Beam Power, Ultra Linear, Triode mode.
Then, there is No negative feedback, Schade negative feedback, and Global negative feedback.
Many of the possibilities are limited, by things like the power transformer:
filament current enough to run the chosen tubes
B+ voltage.
A Cap input filter can give B+ about 1.4X the RMS voltage.
A Choke input filter can give B+ about 0.9X the RMS voltage.
A Modified Choke input filter with a very small input cap can give a B+ voltage that is in-between 0.9X and 1.4X.
Lots of things to try, but pick one or two to start.
Enjoy building.
Enjoy listening!
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I'll be the odd man out and say not to build a single ended EL84 amp with those output transformers. I have used the 25W Edcor transformers up to 20W and they do nicely. I would use them with a higher power design or use a smaller OT (that costs less).
So go with some of those higher power tubes.
Or, parallel 2 or 3 EL84 tubes.
That takes knowledge of some often misunderstood circuit requirements to get good performance.
Or, parallel 2 or 3 EL84 tubes.
That takes knowledge of some often misunderstood circuit requirements to get good performance.
I already bought 'em, so I'll be using them. I'll probably just build a Darling 1626 with them, which is "wasteful" in a sense, but there will be other possibilities in the future. I just want to build something that works and sounds good for now, perhaps learning a thing or two along the way. My speakers sound good with flea watt amps.