The three blind mice - 3 triode LTP?
- By NickKUK
- Tubes / Valves
- 3 Replies
I've been playing with a front end from TubeCad: Cathode-Follower OTL and SIT FETs
Specifically this:
The front end is interesting, the first triode simply puts the signal out via the cathode based on the cathode for bias. The second triode amplifies for the output stage and takes feedback directly from the output - reduced by a 27K resistor. The interesting bit is that it then causes the cathode to bias and thus auto-bias the first triode. (actually input noise will also go up to the B+ via the first and then have anti-phase through the second and output stages).
So.. this got me thinking... Long Tailed Pairs and differential amps and how the auto biasing of the cathode could be used but in a unique way - using three triodes in the LTP.

The first and last triodes provide the standard configuration, however a third (centre) triode is added simply to change the tied cathodes bias based on output feedback (rather than feeding into the grid of the second triode). This then almost replicates the original concept but for LTPs. Not new I suspect but still it seems to make it easier to manage negative feedback without messing with the phases.
Thoughts? (other than lunacy or why waste a triode)
Specifically this:

The front end is interesting, the first triode simply puts the signal out via the cathode based on the cathode for bias. The second triode amplifies for the output stage and takes feedback directly from the output - reduced by a 27K resistor. The interesting bit is that it then causes the cathode to bias and thus auto-bias the first triode. (actually input noise will also go up to the B+ via the first and then have anti-phase through the second and output stages).
So.. this got me thinking... Long Tailed Pairs and differential amps and how the auto biasing of the cathode could be used but in a unique way - using three triodes in the LTP.

The first and last triodes provide the standard configuration, however a third (centre) triode is added simply to change the tied cathodes bias based on output feedback (rather than feeding into the grid of the second triode). This then almost replicates the original concept but for LTPs. Not new I suspect but still it seems to make it easier to manage negative feedback without messing with the phases.
Thoughts? (other than lunacy or why waste a triode)