| Sasquatch |
| Wondering if anyone has tried the second stage of this tube with a load closer to its Rp. All schemos I can find on the web load it with a 5K transformer, yet Rp is 900 ohms. That section could easily handle a less extreme turns ratio for more power. I've got some unused Specos 70v matching transformers that can wired for 2K load. Any suggestions for whether the effort would be worth it or not? Thanks. |
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| mach1 |
| quote: | | All schemos I can find on the web load it with a 5K transformer, yet Rp is 900 ohms |
Check out the plate curves on a 2A3, then look at the 6EM7. The 2A3 curves are pretty reasonably spaced over a wide voltage range. The 6EM7 curves start bunching together as you increase voltage, indicating potential asymmetry along the loadline, which = distortion.
Using a high impedance opt (flatter loadline) helps keep your loadline out of the worst area of bunching. Some people also run the 2A3 and 300B at 5k to minimise this effect.
Another way to minimise the effect of bunching is to run your tube at low voltage and high current - but in the case of the 6EM7 this is not really practical as you will lose too much power running much below 150Vp-k.
In short, 2k way too low if you want reasoable fidelity. The web schemas have got it about right.
Great sounding tube btw. |
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| Geek |
I can backup mach1's explanation with practise. Great tube, but be reasonably light on it. 5-5.5K I found optimal both sonically and on the scope.
Cheers! |
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