Are all at same V3 cathode point except the one for generator check? If yes that's 30.5dB gain (33x) at 100kHz before adding 100kΩ. They also look like skipping about 30pF for RCA and its wire to grid according to Kevin's table (0.35V/6V as someone can make out from photos i.e. -24.7dB). That can be near to the 47pF you mentioned for that wire if we remember that Kevin said 10% table error + 1% error for 600 Ohm generator. There is much extra pF in the construction multiplied by gain along Cag.
At that gain a typical 12AX7 could have 110pF with only 1.5pF assumed added from its base and no extra signal input wiring. I wonder when you put 6N2PEV if it can show the tubes spec difference or if its possible to measure pF between grid and anode base pins with LCR meter as they stand wired with components and everything but when powered down and without a tube in it.
Salas E283CC have different pinout connections
6N2P-EV
An externally hosted image should be here but it was not working when we last tested it.
6N2P-EV
An externally hosted image should be here but it was not working when we last tested it.
OK forget testing the Russian type for now that claims half pF at pure tube level
Assuming experimental error isn't big we would not worry about it since it adds well to the rest pF for your cartridge and 47K load.
But we would still be curious if we could measure a logical pF figure among base pins g, a, (when no tube & no power) with an LCR meter that could verify when added in Miller equation Cin=Cgk+Cga(1+A) what we measure and make out on the table since now we know the gain (A) at 100kHz is 33.3x by the same scope (VppV3cath/VppGen) without added resistor.
Input stage only socket, yes. Second stage does not reflect anything back to the cartridge.
See if it measures anything small pF like 1.5 to 5pF with caps and resistors, if not, try lift one relevant leg to leave only wires in circuit. Especially to cancel R1.
I would buy the Cgk parasitic base pins & layout figure easier as more in expected range and representative for between pins build capacitance.
Those g,k pins had no component interfering across them after you disconnected R1. E2883CC lists 2pF Cgk 1.1pF Cga of its own. CgkTotal=2+6.5=8.5pF CgaTotal=1.1+6.5=7.6pF
Lets plug them in the Miller formula now. Your first stage gain (A) was shown 33x at 100kHz. So Miller = Cgk+((1+A)*Cga) = 8.5+((33+1)*7.6) = 267pF.
It computes well within experimental error of your last findings
So with your same construction & metering if it was for the original design's 6N2PEV which claims own Cga 0.55-0.8pF (we can assume mid ground 0.675pF) and own Cgk 2.35pF it would be 8.85+(34*7.175)=252.8pF
Small difference as the layout+base parasitic remains high and prevents good results.
That's about 100kHz pure Miller, no input wiring extra from RCA input to grid. Kevin, is there a chance is less at 20kHz? Any rework suggestions for losing some parasitic from seeing his base wiring layout photos?
Those g,k pins had no component interfering across them after you disconnected R1. E2883CC lists 2pF Cgk 1.1pF Cga of its own. CgkTotal=2+6.5=8.5pF CgaTotal=1.1+6.5=7.6pF
Lets plug them in the Miller formula now. Your first stage gain (A) was shown 33x at 100kHz. So Miller = Cgk+((1+A)*Cga) = 8.5+((33+1)*7.6) = 267pF.
It computes well within experimental error of your last findings
So with your same construction & metering if it was for the original design's 6N2PEV which claims own Cga 0.55-0.8pF (we can assume mid ground 0.675pF) and own Cgk 2.35pF it would be 8.85+(34*7.175)=252.8pF
Small difference as the layout+base parasitic remains high and prevents good results.
That's about 100kHz pure Miller, no input wiring extra from RCA input to grid. Kevin, is there a chance is less at 20kHz? Any rework suggestions for losing some parasitic from seeing his base wiring layout photos?
Normally shielded wire is a good idea, at the input of a phono stage any appreciable length can contribute additional capacitance. I suspect the wire you are using might be contributing some capacitance - would be good to measure it. You can get close with your meter with nothing powered. Anything over 40 - 50pF would I think be justification for trying something else.