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|12th September 2005, 08:25 PM||#1|
Join Date: Oct 2004
Many customers have asked us to build higher gain tubes. We are working on a series of those tubes. In the pipeline is a direct replacement for the obsolete AVVT 20B. As a spin off from this project, we plan to make a family of those tubes! The idea is to make:
EML 20A. 20x gain tube for pre-amp or driver applications
EML 20B 20x gain tube for driver or output applications
EML 30A or 30B 30x gain tube for pre-amp or driver applications
With the 20B you can replace the complere driver + pre-amp, using ONLY this tube. For a 300B you need 60Volt AC on the grid. So you need an amplification of 60x. With the Lundahl transformers it is possible to use a 4x step up transformer and the total output signal will be 60..80Volt coming out of the transformer.
Another option is to use a 4x input step up transformer. This is even better, because now you replace the (noisy + humming....) input tube by a transformer! So from 1 Volt AC input, you make 4Volt signal with the transformer. This is amplified by the 20A, and gives around 70Volt, resistor loaded, or 75Volt choke loaded. The 300B needs only 60Volt, so you will have below 1Volt input sensitivity! The complete amplifier can now be made from one 20B and one 300B tube.
For resistor loaded, the 20B may be better, because it can do higher power. The choke loaded stage can be made with the 20A at somewhat lower power, since a choke loaded tube is running almost unloaded for the AC output signal.
The input transformer will also give you perfect input isolation, and cancel any hum coming from the input cables. This is why the Japanese LOVE input transformers so much. (and not only the Japanese) .
For the real freaks... It is possible to build a COMPLETE amplifier ONLY from the new 30A. This tube has enough output power to give a few Watt. For full output signal it needs something like 7Volt on the grid. This can be done with an input transformer, with for instance a step up factor of 5x. The result is 1,4 Volt input sensitivity! Most CP players and pre.amps can give this voltage. With the 20B something simular can be done, and this tube will give more output power than a 2A3 tube even! So the whole 20B amp will have only one tube!!!
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