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Old 15th June 2012, 01:55 PM   #61
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How are the JJ EL34's? I was thinking I could make my new amp EL34 friendly (wiring wise) but only if I can find a reliable brand. I've been reading that new EL34's aren't as tough as the old ones. The issue is that my power transformer is giving me about 520Vdc (my house is at 123Vac).

*edit* Duh, just re-read and you said EL84 not 34...
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Old 15th June 2012, 02:38 PM   #62
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Yeah, they're 84's. I've got nothing to compare them too, as they are my first set of EL84's, and they're in the first amp I built, but they work good. JJ still has the best known reliability as far as I know, and the E34L's are supposed to be pretty bulletproof operating within ratings.
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Old 15th June 2012, 02:47 PM   #63
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Quote:
Originally Posted by Stormrider View Post
JJ still has the best known reliability as far as I know, and the E34L's are supposed to be pretty bulletproof operating within ratings.
I just read a review of the JJ 6CA7 which sounds pretty good too. The problem I have with making my new amp EL34/6CA7 friendly is that when I put in a 6550 I'll either have to re-bias or accept the fact that I'm not using it to its fullest potential. haha
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Old 18th June 2012, 02:41 PM   #64
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Comparing the datasheets of the JJ EL34/E34L, 6CA7, and the KT77 I don't really see where any significant operating differences would be, or why they would sound different assuming the conditions were matched for each valve. But, they are all within 10$ per pair of each other, so the point is moot. Only other valves in this family I'd consider would be the new production Mullard EL34 or the EH EL34/6CA7.

If you're planning on running a 6550, I would design around that and stick with it for an SE amp. If it was a quad P-P design or something I could understand wanting the flexibility as the prices of matched quads of 6550 or KT88 are quite high, compared to EL34 but if you only need one...
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Old 19th June 2012, 02:52 AM   #65
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From what I've read those tubes all have different construction even though the specs are the same, obviously causing different character in the sound. For my SE project I'm just not sure what sound I want. I'll probably experiment between a bunch of tubes and cathode vs fixed bias also to see how they all sound.

Funny you would mention a quad PP amp. Just today on my way home (3 hour drive) I was thinking I'd like to build a heavy mono-block, quad 6550 or EL34. Give it buffered high-Z and low-Z inputs.
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Old 19th June 2012, 12:15 PM   #66
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Here is my plan for the output stage:

Click the image to open in full size.

V1, V2 are 6L6GC, V3A/B is a 12AX7. Most of the resistor values are preliminary, as I haven't done any load lines for the cathodyne, but it should be close. Nothing special here really, just a basic cathodyne with the valvewizard tweaks.

OT is an Edcor 60W with a 4.2K primary and 4, 8, 16ohm secondaries. The Edcor has 40% screen taps, so I'm thinking about adding the ability to switch from pentode to ultralinear. I have to do the calculations to see if the power increase would be worth the complication.
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Old 19th June 2012, 01:55 PM   #67
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Looks good, but the 100K and 1.8K seem a bit far apart, but as you said you still have to do the math on them.

Should sound awesome. What kind of sound are you going for? It seems a bit mixed because I thought you were tagetting metal/aggressive sound, but then a cathodyne is there, and then fixed bias PP. It looks cool to me, but just not clear if it will be the sound/feel that you're going for.
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Old 19th June 2012, 02:08 PM   #68
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A standard LTP would probably make more sense as far as tradition is concerned, but I know the cathodyne can sound just as good for high distortion metal tones.

I am worried about the V1A gainstage overdriving it too hard, and this will be purely conceptual before I get through Merlin's book. As of now though, I like the plan. Reminds me of an ST70.
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Old 19th June 2012, 03:10 PM   #69
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What is your B+3 voltage? For the cathodyne you should have as high a B+ as possible to keep the clean headroom up. For mine I ran the screen voltage through a choke to supply the cathodyne. Worked well.
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Old 19th June 2012, 03:15 PM   #70
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B+3 target will be around 360Vdc. I'm going to do without a choke, and use the cap multiplier to feed everything except the power tube plates. I've redrawn the PS schematic to show this:

Click the image to open in full size.
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