Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on April 18, 2013, 06:31:42 pm
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I have a homebrew thats similar to a master volume marshall and recently have been using 6L6's. I switched because winged C EL34's are going the way of the dinosaur and i can't find another 34 i like near as much, but i found i may like 6L6 better than them all Maybe even the winged C ! So now this has me wondering...
1)- if i scrapped the 3.2k OT for one made for 6L6 (what is that, about 6k?) what would i hear tonally compared to the 3.2k with 6L6?
2)-who besides SED makes a good 6L6? (current prod.) Using JJ's right now but generally i always seem to find any JJ tube i use is almost always average at best.
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You could use the same OT without changes.
Maybe for a given supply voltage, 6L6 might typically use 4kΩ instead of 3.2kΩ, but the difference is not worth the price of a new OT.
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Yeah, thats not much. I thought it was typically more like 5 or 6k. In any case, what sort of difference would there be regardless of whether it's only a small change?
I already am using the same OT by the way, just wondering what a higher impedance OT would sound like with 6L6.
Also, anyone want to suggest how the JJ's are compared to others and what current tube is generally considered better?
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It will probably make less output power than you're getting now, but I doubt the change would be, "Wow!"
The quantity or quality of distortion might change, but that would also depend on the core size of the new OT vs that of the old OT.
Are you already using the stock Bandmaster OT or something else?
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No, it's a marshall style amp with a mag comp JCM800 style OT, 3.2k.
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> typically more like 5 or 6k.
Best load is determined by the power you want and the B+ voltage.
That assumes your tubes are "big enough". There's no huge diff 6L6 or EL34, they are comparably big.
So with the same B+, a switch from 3K to 6K tends to cut your power in half. Since you have not halved the power transformer weight, that's a poor deal.
Any tube can be run at high or low load impedance. In the past, some 6L6 users favored higher voltages (at lower current); hence 6.6K load was often seen.
But the B+ cap costs are high when you get over 450V-500V.
So both Fender and Marshall explored ~~400V supply and lowered the load impedance to suck more power. The big 5881/6L6GC Fenders run 4K per pair.
EL34 will pass a wee bit more current, at the same G2 voltage, than 6L6 types. Marshall pushed down to 3.4K. It's not a huge amount more power; also your *speaker* impedance varies more than 3.4:4 ("8 ohms" can be 6 or 10 ohms minimum, and more outside the midrange).
Leave the OT alone. Just check the bias.
Also explore 6550. Costly, but bullet-proof in EL34 duty.
Watch Pin 1. On EL34 this is usually tied to Cathode. On metal 6L6 (don't use these) and good 6550, pin 1 is the metal shell. On fix-bias amps, it makes little difference. On cathode-biased rigs, if you drop the pliers between the metal shell and the chassis you may short-out the cathode resistors and cook the tubes.
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Thanks PRR. I'll just leave it then. It's fixed so no problem with pin 1 being tied to 8, and I already biased it so good to go. I just wanted to be sure i wasn't sacrificing tone even tho it's good as is. I'm also liking the JJ 6L6 now, and thats something that usually doesn't happen. (i never seem to like JJ's of any type) I've tried 5660's and even have a old RCA pair i think they are....or some USA production. But i find them a little too hard. The JJ 6L6 really seems to sound like a EL34 but more balanced with sweeter highs. I think I like them as a EL34 more than the winged C 34's !