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The shoot-out !
I re-wired the chassis so that I could run either the 6E5P or the 6P15P. Only one tube can be installed at a time since the two sockets are more or less wired in parallel with each other. This results in the same cathode bias (amber LEDs), the same plate feedback capacitor (220nF 630V film) and the same screen supply (10k + 100uF 500V, followed by 4k7) but with individual 1k stoppers on the respective control grids. Because of this simplistic approach the operating conditions are slightly different - but then so are the tubes.
6E5P:
B+ 243V
Va 240V
Vg2 195V
Vk 3.8V
Ik 22mA
6P15P:
B+ 239V
Va 236V
Vg2 175V
Vk 3.8V
Ik 29mA
And since I was a bit quick off the bat in evaluating the Edcor - I don't think conditions were the same between tests so this needs to be repeated. I've mounted both OPTs on the chassis and wired a DPDT switch to choose which one to listen with.
Now the shoot-out can begin
I re-wired the chassis so that I could run either the 6E5P or the 6P15P. Only one tube can be installed at a time since the two sockets are more or less wired in parallel with each other. This results in the same cathode bias (amber LEDs), the same plate feedback capacitor (220nF 630V film) and the same screen supply (10k + 100uF 500V, followed by 4k7) but with individual 1k stoppers on the respective control grids. Because of this simplistic approach the operating conditions are slightly different - but then so are the tubes.
6E5P:
B+ 243V
Va 240V
Vg2 195V
Vk 3.8V
Ik 22mA
6P15P:
B+ 239V
Va 236V
Vg2 175V
Vk 3.8V
Ik 29mA
And since I was a bit quick off the bat in evaluating the Edcor - I don't think conditions were the same between tests so this needs to be repeated. I've mounted both OPTs on the chassis and wired a DPDT switch to choose which one to listen with.
Now the shoot-out can begin
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heheheee. This is why I'm really looking forward to finally doing this. With such a simple circuit it doesn't take much time and/or effort to switch things around like that.
Maybe you mentioned this already but what are you loading these little buggers with? I'm curious if the primary impedance difference in the trafo's is what you're hearing. I'd also guess that the difference is more profound in the 6P15 between the two trafos?
Just kind of....back of the napkin...looking at curves and trying to postulate what the steeper load line might sound like.
Maybe you mentioned this already but what are you loading these little buggers with? I'm curious if the primary impedance difference in the trafo's is what you're hearing. I'd also guess that the difference is more profound in the 6P15 between the two trafos?
Just kind of....back of the napkin...looking at curves and trying to postulate what the steeper load line might sound like.
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Very good question - it's probably worth exploring more than I did.
I found for both tubes that with the plate to screen feedback cap in place the sweet spot on the Hammond was a 5k load. The 10k was better when in tetrode/pentode without the screen feedback but of course it swings more plate voltage which doesn't suit my limited power supply (the 6P15P can take 300V). The Edcor gives no choice, it's fixed as a 3k5 load with 8R speakers. I didn't find a profound difference between the Edcor and the Hammond (at 5k) with either tube. The Hammond had a bit more treble sparkle but they were both very competent. Considering the price of the Edcor it would be the sensible choice. I'd be happy to use the Edcor but it's a loaner. Since the Hammond is mine I will use it (at 5k) when I do a final build on a fresh chasis.
Go for it - this messing about with a single tube is really a great way to gain some experience, without a lot of effort too. And the experimental chasis is well worth investing the time to set up so that you can mess about without worrying about scratches and a few extra holes.
I didn't mess about with the steeper load line much; you may find a better operating point.
I found for both tubes that with the plate to screen feedback cap in place the sweet spot on the Hammond was a 5k load. The 10k was better when in tetrode/pentode without the screen feedback but of course it swings more plate voltage which doesn't suit my limited power supply (the 6P15P can take 300V). The Edcor gives no choice, it's fixed as a 3k5 load with 8R speakers. I didn't find a profound difference between the Edcor and the Hammond (at 5k) with either tube. The Hammond had a bit more treble sparkle but they were both very competent. Considering the price of the Edcor it would be the sensible choice. I'd be happy to use the Edcor but it's a loaner. Since the Hammond is mine I will use it (at 5k) when I do a final build on a fresh chasis.
Go for it - this messing about with a single tube is really a great way to gain some experience, without a lot of effort too. And the experimental chasis is well worth investing the time to set up so that you can mess about without worrying about scratches and a few extra holes.
I didn't mess about with the steeper load line much; you may find a better operating point.
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A spud in your pocket, I like that idea
Anyhow, I've started the process of drilling holes and slapping some paint on the OPT...
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Did you bake this tater yet or is it still in the oven?
Just got my headphone amp up and choochin last night so once I find a proper chassis for it at the antique store tonight and get that all wired in I think I'm going to spud one. I've got a pair of bookshelf speakers that would fit this well. I've been finding that I'm listening more to my tubes than my (admittedly) cheap-ish yamaha all-in-one......so I'm finding excuses to convert all my stuff over
Just got my headphone amp up and choochin last night so once I find a proper chassis for it at the antique store tonight and get that all wired in I think I'm going to spud one. I've got a pair of bookshelf speakers that would fit this well. I've been finding that I'm listening more to my tubes than my (admittedly) cheap-ish yamaha all-in-one......so I'm finding excuses to convert all my stuff over
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The chassis is tight, and point-to-point wiring is tricky. I'm thinking about using the main power supply capacitor as a place to mount the rectifier diodes, bleeder resistor and the diode series resistor. I've fashioned a small piece of copper-clad board to fit over the terminals of the capacitor (it's one of those 3 terminal capacitors). It might just work.
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OK, the build-out has gone well and I am now listening to the little Golden spud.
I included a switch to select between 'Yukon Gold' and Pentode mode. The Yukon Gold mode being with plate to screen-grid feedback for treble (as per all the listening tests) for use with speakers that have a rising impedance in the treble and benefit from some bass-lift (i.e. small single full range drivers).
I measure:
B+ 259V
Plate-Cathode 252V
Screen-Cathode 182V
Cathode 3.79V
screen current approx 5mA
I included a switch to select between 'Yukon Gold' and Pentode mode. The Yukon Gold mode being with plate to screen-grid feedback for treble (as per all the listening tests) for use with speakers that have a rising impedance in the treble and benefit from some bass-lift (i.e. small single full range drivers).
I measure:
B+ 259V
Plate-Cathode 252V
Screen-Cathode 182V
Cathode 3.79V
screen current approx 5mA
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