Member
Joined 2009
Paid Member
It doesn't make any sense to me why there are warnings (not just this thread) to avoid the self-inverting output stage because of limitations on the power output as long as it's accepted that it only operates in Class A.
If comparing with other phase inverter approaches also operating in pure class A surely it's equivalent. Compared with another amplifier that uses, for example, a concertina or LTP phase inverter, with the power tubes at the same operating point, all these topologies can swing the same Class A current into the same load.
It may seem wasteful to build an amplifier that's unable to take advantage of a little Class B action but we don't build tube amplifiers for their efficiency and some folk like to keep things purely in Class A, or maybe attracted to a particular topology for reasons of their own.
I guess most of us are aware that another 3dB of output power will make little difference to the perceived volume capability of the amplifier anyhow.
If wanting to build a two-stage class a PP without transformer phase splitting (in input nor as interstage), wouldn't a direct input long tailed pair give better performance than the topology discussed in this thread? E.g. http://ekingsbu.users4.50megs.com/audio.html
brightcity,
Are you still active on this thread?
Are you still trying to use those push pull output transformers that you have?
What are you trying to build?
A guitar amp?
A Hi Fi / Stereo amp?
How much power are you needing?
What are the specifications of your push pull output transformers?
What did you mean by a "5 primary transformer"?
Did you mean a primary with 5 leads: plate, UL, center tap, UL, plate.
If you do not have the UL taps, then Triode; Triode wired pentode/beam power mode; and pentode/beam power mode can be made to work.
I am sorry for all the questions.
But someone has "opened" this thread again.
Let us come to a reasonable solution of how to use your push pull output transformers; or to do something completely different.
Others,
A comment about any who say there is no phase inverter needed if you build a self inverting output stage.
A self inverting output stage IS the phase inverter; it is just left to the output stage to do the phase inverting instead of an earlier phase splitter stage.
As was correctly noted earlier, the self inverting phase inverter needs 2 x the voltage drive, versus using a phase inverter before the output stage.
But an earlier stage that is a cathode coupled LTP phase inverter, needs 2 x the signal at its input to get the expected voltage output.
6dB relative voltage gain loss due to the self inverting output stage, versus 6dB relative voltage gain loss due to the cathode coupled LTP phase inverter. One question is: where do you want to put the 6dB loss of relative gain?
Simplicity has its tradeoffs.
Are you still active on this thread?
Are you still trying to use those push pull output transformers that you have?
What are you trying to build?
A guitar amp?
A Hi Fi / Stereo amp?
How much power are you needing?
What are the specifications of your push pull output transformers?
What did you mean by a "5 primary transformer"?
Did you mean a primary with 5 leads: plate, UL, center tap, UL, plate.
If you do not have the UL taps, then Triode; Triode wired pentode/beam power mode; and pentode/beam power mode can be made to work.
I am sorry for all the questions.
But someone has "opened" this thread again.
Let us come to a reasonable solution of how to use your push pull output transformers; or to do something completely different.
Others,
A comment about any who say there is no phase inverter needed if you build a self inverting output stage.
A self inverting output stage IS the phase inverter; it is just left to the output stage to do the phase inverting instead of an earlier phase splitter stage.
As was correctly noted earlier, the self inverting phase inverter needs 2 x the voltage drive, versus using a phase inverter before the output stage.
But an earlier stage that is a cathode coupled LTP phase inverter, needs 2 x the signal at its input to get the expected voltage output.
6dB relative voltage gain loss due to the self inverting output stage, versus 6dB relative voltage gain loss due to the cathode coupled LTP phase inverter. One question is: where do you want to put the 6dB loss of relative gain?
Simplicity has its tradeoffs.
Last edited: