As far as I can see from the classic texts you can only describe as "grounded grid" a circuit where the input signal is applied between cathode and ground with the grid connected directly to ground, which is not the case with the Berning circuit. Does he call it "grounded grid". I think we can say that Rozenblit was definitely wrong to use that term for his circuit.
No, I would call that a hybrid cascode. In my view 'grounded grid' should be reserved for a stage containing a single valve with input to the cathode and output from the anode. Mainly used for UHF in the old days, but could perhaps be used for MC or DAC where the low input impedance is helpful.SY said:
I regard 'grounded' in this contect to mean AC grounded, although the classic circuit usually has the grid DC grounded too.
I know the upper valve in a cascode operates itself in grounded grid but the lower valve operates as grounded cathode yet we don't call the whole circuit grounded cathode - we call it a cascode so we all know what we are talking about.
There is a fuzzy line, because as well as the classic series cascode there is also the parallel cascode where both valves get full HT/B+, with a coupling cap from first anode to second cathode. In that case I would call it a cascode if there is no impedance matching between the valves, and a grounded cathode followed by a grounded grid if there is impedance matching.
Dave, it's not any kind of cascode. Squint at it for a few minutes.
b, the signal from the source follower is applied between cathode and grid of the gain element (the tube). If the source follower were in a different box, and the input to the preamp box were directly at the cathode, would it then be a grounded grid by your definition?
b, the signal from the source follower is applied between cathode and grid of the gain element (the tube). If the source follower were in a different box, and the input to the preamp box were directly at the cathode, would it then be a grounded grid by your definition?
OK, I hadn't spotted that they were P-channel FETs. This is a semi-inverted hybrid version of the cathode-coupled amp. The valve itself operates in grounded grid, but the circuit stage is not GG. We do not usually name an entire unit after one sub-circuit within it: lots of preamps contain a follower, but we only call the preamp a follower if a follower is the main signal handling part of the circuit and not just an output stage. In the same way, a circuit which uses a valve in grounded grid is not a grounded grid preamp if the actual circuit is a cathode-coupled stage (whether hybrid/inverted/series or parallel).
One of my peculiarities is that I hate misleading names for technology. I know some bad names have stuck, but we don't have to introduce new ones.
One of my peculiarities is that I hate misleading names for technology. I know some bad names have stuck, but we don't have to introduce new ones.
Maybe, yes. If a circuit stage is split between boxes does that make it two stages or one split stage? I think the answer is to call it the name which will most clearly describe how it works. Maybe I would say "The follower in box A and the grounded grid amp in box B together form a hybrid inverted source/cathode-coupled amplifier."
However, there are no borders in the circuits being considered so it is a theoretical point. Complex circuits can always be partitioned for analysis in more than one way and sometimes a circuit has features of more than one classic configuration. However, a short-tailed pair is a short-tailed pair and should not be called a grounded grid!
However, there are no borders in the circuits being considered so it is a theoretical point. Complex circuits can always be partitioned for analysis in more than one way and sometimes a circuit has features of more than one classic configuration. However, a short-tailed pair is a short-tailed pair and should not be called a grounded grid!
Last edited:
By the definition I use (which is that of the radio engineers who devised for their output stages) the Berning circuit is not a "grounded grid". After all a "cathode-coupled" circuit has a cathode follower at its input, which is analogous to Berning's FET stage, and the essence of the controversy with Rozenblit is that we do NOT call that a "grounded-grid" circuit. After all, as DF96 has adduced, a cascode can have a grounded grid in its second stage and we call it a "cascode" not a "grounded-grid" ; as can a "long-tailed pair", and we do not, etc.etc.
So you're saying, yes, if they were in two separate boxes (e.g., a signal source with a follower output driving a line amp with input to the cathode), you'd be fine with calling it grounded grid. Appreciate the clarification, guys!
(as you can tell, I'm agnostic on the issue despite being a stickler myself for terminology)
(as you can tell, I'm agnostic on the issue despite being a stickler myself for terminology)
DF96 may be saying that but I'm not. Neither the Berning nor the Rozenblit circuits are "grounded-grid". The only audio use I can remember was a Manley preamp where it was used for moving coil cartridges, which have low output impedances. Otherwise it's a radio output stage, the input to which I have no knowledge of. I can't see what you're trying to "clarify".
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.