Re-calculating feedback resistor value after tube change in Leak TL12

Tubes Asylum

Questions about tubes and gear that glows. FAQ

147.8.157.207

I have read from somewhere that the input tube in the Leak TL12 can be changed from pentode to triode operation. For those unfamiliar with this amp, the arrangement is thus: 3 amplification stages, with an EF37A input tube, an ECC33 (or 6SN7) long tail pair phase splitter driving a pair of triode-wired KT66. Global feedback (26dB) is taken from the OPT secondary back to the cathode of the EF37A. Input sensitivity is very high at around 150mV.
If I wire the EF37A as triode, this will reduce the noise but also result in considerably lower open loop gain. The question is, how should I change the feedback resistor value? Changing the tube to triode operation will considerably lower plate resistance, and this together with the reduced Mu will change the cathode resistance, which is in parallel with the cathode bias resistor. Any ideas?

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

Topic - Re-calculating feedback resistor value after tube change in Leak TL12 - adrian 00:58:39 12/27/00 (1)

Re: Re-calculating feedback resistor value after tube change in Leak TL12 - Kevin Elliott 11:47:30 12/27/00 (0)

You can not post to an archived thread.