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In Reply to: RE: Pros and Cons of 300B PSE and PP posted by deafbykhorns on March 28, 2025 at 10:55:54
I plan to use this OPT
https://www.hammfg.com/files/parts/pdf/1645A.pdf?v=16976619456SN7 long tail pair inverter stage and 6J5 gain stage. I remember when I did KT88, used a tube as the current source to replace 6SN7 cathode resistor.
Edits: 03/28/25 03/28/25
If you are direct connecting your phase inverter to the input gain stage you will have more than enough voltage available to use a simple but very effective cascode MOSFET CCS as a tail impedance. Forget using LM317. Order some IXYS 8N100D2s from Mouser while they are still available. These devices are becoming harder to come by and may by obsoleted in the future.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
The maximum voltage drop on CCS I want to go is 20V. So directly coupling gain stage is not possible.
The 8N100D2 is rated for 800V. The cascode CCS achieves it's best performance at 30-40V across it. I just built an amp with the input stage DC coupled to a 6SN7 long tailed phase splitter at 110V. Why the limit of 20V?
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
My V+ is only 350V. If CCS takes 50V, 6SN7 only has 300V. To output 140V peak-peak to driver 300B, the harmonic distortion will increase to 1.9%.
Edits: 04/13/25 04/13/25
Build a small negative PS. It doesn't have to be very elaborate or expensive. My phono pre, line stage and mono-blocks all have neg. PSs to accommodate CCS tails. The sonic difference in CCS tails is real and noticeable. It's worth the effort.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Another thought. I can do a -100V negative regulated PS. 100V on CCS. 350V on 6SN7 for inverter stage. 200V on 6J5 for gain stage. It has no issue to output 10V peak to peak to drive 6SN7.
Edits: 04/13/25
I am going to use a SMPS for my V+ power supply. I cannot use the negative PS you suggested.
Edits: 04/13/25
Why? The neg. PS is floating until you attach the pos. to ground. Also, the CCS only needs 30-40V across it . No need for 100V.
v
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
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