So, a triode LTP PI can easily introduce inaudible CM hum from B+ ripple?
That would advocate stiff filtering, a second CCS or the use of penthodes.
That would advocate stiff filtering, a second CCS or the use of penthodes.
As always, large values of B+ ripple are a problem.
Do not use a CCS in both the cathodes and the plates (that does not work, causes other problems, widely discussed in other threads).
Do not use pentodes to fix B+ ripple.
Pentode plates with a resistive load to B+ have Less hum rejection.
Fix the problem of the B+ ripple, do not complicate the tube circuit just to compensate for poor B+ filtering.
Do not use a CCS in both the cathodes and the plates (that does not work, causes other problems, widely discussed in other threads).
Do not use pentodes to fix B+ ripple.
Pentode plates with a resistive load to B+ have Less hum rejection.
Fix the problem of the B+ ripple, do not complicate the tube circuit just to compensate for poor B+ filtering.
B+ hum is a slightly different issue from heater hum. For an LTP:
A (ripple) ac voltage appearing at the common cathode is common to both tube halves and will appear at both outputs. Amplified by the gain of the tube.
A ripple voltage on the B+ line will also appear at both outputs but not amplified.
So stiff filtering yes, second CCS no, pentode no. If you're interested in ripple/hum cancellation look up Broskie and his TubeCAD. He writes extensively about methods of ripple cancellation.
If ripple is coming from the B+, than fix the B+.
If ripple comes from a filament to cathode interface, then use a better tube, elevate the filament, or do both.
Do not put a ripple cancellation bandaid on the amp to fix ripple. A cancellation is a Null.
Nulls are sharp (narrow).
A cancellation scheme (Null) only has to change a little bit to go from great, to good, to bad.
Too hard to set, too hard to replicate, too hard to make it the "solution" of choice.
Just my opinion.
If ripple comes from a filament to cathode interface, then use a better tube, elevate the filament, or do both.
Do not put a ripple cancellation bandaid on the amp to fix ripple. A cancellation is a Null.
Nulls are sharp (narrow).
A cancellation scheme (Null) only has to change a little bit to go from great, to good, to bad.
Too hard to set, too hard to replicate, too hard to make it the "solution" of choice.
Just my opinion.
Thanks for your replies gents. Off topic: comparing triode vs penthode LTP, is there a principal difference in accuracy while operated from a tail CCS?
The large impedance of the penthode resembles the CCS impedance, where a typical triode has >100 times less internal resistance. Also, G2 behavior seems a little cloudy as it can both sink and source current, although that will probably even out.
The large impedance of the penthode resembles the CCS impedance, where a typical triode has >100 times less internal resistance. Also, G2 behavior seems a little cloudy as it can both sink and source current, although that will probably even out.
Not clear what you mean by "accuracy".
Both triode and pentode LTP can be designed to be very good. There are high and low gm triodes and pentodes. You need to make a design choice based on what they are driving and your other requirements.
I don't understand your comment about g2.
Both triode and pentode LTP can be designed to be very good. There are high and low gm triodes and pentodes. You need to make a design choice based on what they are driving and your other requirements.
I don't understand your comment about g2.