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6sn7 direct coupled and transformer coupled

Hi I was wondering what are the changes that must be done in the second version (direct coupled) of the next preamplifier in order to use a 6-7K transformer at the anode of the second tube instead of the 5mf capacitor coupling
 

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kevinkr

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neazoi said:
Hi I was wondering what are the changes that must be done in the second version (direct coupled) of the next preamplifier in order to use a 6-7K transformer at the anode of the second tube instead of the 5mf capacitor coupling


You can't use such a transformer in the anode circuit of a single 6SN7, you need ~ 3X rp for good performance - you can get away comfortably with 15K primary impedance if the primary inductance is high and the secondary is lightly loaded. (i.e. > 600 ohm load)

Why you would want to is beyond me.. A single 6SN7 or pair of 6J5 with transformers should provide enough gain for most line stage applications. (About 6dB - 12dB depending on load at the secondary for a 15K:600 transformer.)