@GuidoR I am becoming a fan of the sound of laterals too. I haven't built the more complex higher power amps, but I want to try in the future. Maybe an SCG driving a PP lateral output stage.
With respect to the beefy driver, I started with the SCG buffer, and while it sounded great, it also sounded a bit thin and wimpy, and some loud passages were even screechy. But it showed a lot of promise, and Erno Borbely's articles mention that the laterals need a good amount of drive. So, I tried it with a beefier drive and the thinness was gone, the 'struggle' sound was gone, and it gave way to a glorious, organic sound. Check out the attached article. Erno looks at the slew rate and current drive needed for a 30V swing at 40 kHz and then comes up with 7.5 mA and then gives a rule of thumb of increasing it five times for > 30 mA drive. We're don't have that big a swing with the ElMo, but still I found at least 20 mA drive, perhaps more, is needed for them to sound the best.
The Triad would be fine but its resistance of 50 ohms will mean you will get about 70 mA of current to get the bias point right for the output FET (about 3.4V based on LTSpice for about 2A of output bias). A little more resistance ~70-120 ohms would be better. I am using the Hammond 156M, which puts it in the zone. Please note that I have not finished building this amp yet. Right now, I'm using a beefy buffer on the SCG output and then AC couple that output to the lateral.
With respect to the beefy driver, I started with the SCG buffer, and while it sounded great, it also sounded a bit thin and wimpy, and some loud passages were even screechy. But it showed a lot of promise, and Erno Borbely's articles mention that the laterals need a good amount of drive. So, I tried it with a beefier drive and the thinness was gone, the 'struggle' sound was gone, and it gave way to a glorious, organic sound. Check out the attached article. Erno looks at the slew rate and current drive needed for a 30V swing at 40 kHz and then comes up with 7.5 mA and then gives a rule of thumb of increasing it five times for > 30 mA drive. We're don't have that big a swing with the ElMo, but still I found at least 20 mA drive, perhaps more, is needed for them to sound the best.
The Triad would be fine but its resistance of 50 ohms will mean you will get about 70 mA of current to get the bias point right for the output FET (about 3.4V based on LTSpice for about 2A of output bias). A little more resistance ~70-120 ohms would be better. I am using the Hammond 156M, which puts it in the zone. Please note that I have not finished building this amp yet. Right now, I'm using a beefy buffer on the SCG output and then AC couple that output to the lateral.
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Oh absolutely, adding 20-30 ohms would work fine. Juma’s circuits and threads are always fun and informative. Will check them out.
If my calculations are correct, for a 10W output @40KHz the SR would be 3,14 V/uS, and the current needed to drive LATFET's gate (Ciss 600pF) would be 1,9 mA, thus I am confident that my 2SK170 - based buffer biased at 10mA, even if then divided by xformer ratio 1:4 = 2,5mA, would have enough cojones.
Unfortunately here the weather is getting very hot, summer is approaching and it is not suitable for class A projects, so all my projects are slowing down (like my avatar...)
Following anyway with interest your adventure...
Guido
Unfortunately here the weather is getting very hot, summer is approaching and it is not suitable for class A projects, so all my projects are slowing down (like my avatar...)
Following anyway with interest your adventure...
Guido