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Original Message

A possible selective feedback for circlotron

Posted by 6AS7_6SN7 on October 12, 2010 at 01:49:57:

'Mutatis mutandis' I think this selective feedback network can be applied to the majority of commercial circlotrons.

The selective feedback network is made of R13, R22, R21, R20 and C5.

The feedback signal is picked across the normal speaker output (paying much attention to the polarity to prevent wild oscillation).

In this example there is room for about 11 dB feedback at low/mid frequency, 7.5 dB at 10 KHz, 3 dB at 20 KHz and zero feedback above 30 KHz.

Changing the value of C5 will allow to increase or decrease the 10-20KHz feedback.

Changing the value of R13 and R20 allows to trade in more low frequency feedback (i.e. lower output impedance) in exchange for reduced mid-band gain.

Best Regards
Luca