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Re: Won't 4k ohm OT in Lightning eat EL84s?


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2/5/2000 12:15 AM
Carl Z
Re: Won't 4k ohm OT in Lightning eat EL84s?
Speed;  
 
I kinda think that some of the greatest ideas come from accidents or just plain old laziness on the part of the designer. I can see Mark Sampson saying..."Damn, I need a tranny with 8k primary but only have this 4k sitting here. Awww screw it, I'll use it anyway. Hey, that sounds pretty darn good!" And the rest is history.  
 
Remember we're making music making equipment. Don't get too tied up in knots over all the theory. It won't necessarily sound better if you do it "by the book"  
 
Regards;  
Carl Z
 
2/5/2000 12:55 AM
Farrow
6 of 1...
Well, I run my Pro Jr into a 4ohm load all the time (open-back Fender 2x12 cab) and it sounds great! So maybe running your EL84s at 4K isn't a bad thing. We're not playing stereos, we're guitarists, right? So screw the theory (to a point...) and do what you think sounds best.  
 
What I'd do? Get the 8K tranny with 16, 8, 4ohm taps. That way you can have whatever load you like and you can pick the one you like the best. No sense building an amp you don't like, right?
 
2/7/2000 12:21 PM
SpeedRacer
Re: Won't 4k ohm OT in Lightning eat EL84s?
I hear ya Carl.. and thought my reply was pretty clear about that actually. Sorry if it wasn't! I didn't diss Mark about his load/methodology.. Yes he threw theory out the window (which can be a good thing, yes) I think I even went so far as to point out that I have tone-hound buds who swear by this set up (they use AC30 OT's FWIW). I just don't personally think it's a great idea and I don't think tubes need to be run on the 'hairy edge' to sound their best. (look at Va vs load imp in a 'Wreck or a Z for instance!) That's just me though. :-) I'm not a big theorist myself - my only design rules are "does it sound good?" and if the answer to that is "yes", then Q#2 is "will it hold up on stage or will it melt." That's a big one for me.
 
2/7/2000 1:20 PM
Carl Z

SpeedRacer;  
 
Usually when I work up an amp design I'll take a goal and see what basic setup i want to use. After that I do enough math to know I'm not going to roast any parts and tweak from there. I've wound up with some very strange values every once in a while. Not exactly hard science but every time i've done an amp "by the numbers" it's always sounded like crap.  
 
Regards;  
Carl Z
 
2/7/2000 4:13 PM
SpeedRacer

Sounds like we're doing the same thing. :-) My goal is always first and foremost to make a musical instrument. Everything else is secondary. I think the best case of "???" tweaking for me was having Trace Allen by the lab to show off that parallel PI cap tweak. It's the sort of thing I would never have even tried on my own.. after all the change in net uF is tiny, people are not "supposed" to hear things like small phase changes etc etc. Yet when we hooked up some cap sub boxes and tweaked in and out.. there it was. Why it works is someone else's problem. :-) It just does.  
 
>>..After that I do enough math to know I'm not going to roast any parts and tweak from there. <<  
 
that's the ticket right there!
 
2/5/2000 3:13 AM
Mike B

I've built a couple of Spitfire/Lightning clones and I've experimented with primary Z quite a bit. Yes, running a lower primary Z is harder on the tubes, but in this case the tonal result is worth it, IMHO. The 4K load results in greater harmonic content and a "beefier" tone, for lack of a better word. I've done side-by-side comparisons and the differences between 4K and 8K are very noticeable to my ears. I think it's worth experimenting with this to see what you like....  
 
Mike B
 
2/5/2000 10:57 PM
Randy Jamz

What's wrong with this picture? Lower primary impedance is NOT harder on tubes. The worst you'll do is an inefficient match, with less output wattage. Plate voltage/Screen voltage/Bias voltage is what determines what is harder on the tubes. The 8K suggestion from tubes manuals since the late 1200's is only that... a suggestion. My guess is that 3800 ohms is a pretty common 6L6 tranny, and someone just happened to have one laying around the house and figured on using it with 6BQ5's. With a 3800 ohm primary, each tube 'sees' 950 ohms. Measure your output wattage. Well, that's about all the time I have for now.
 

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