There is pretty lengthy message on the carton side of O-T-3:
"Manufactured for the O. & T. ELECTRIC. CORPORATION 1819 Broadway, New York By the DE FOREST TEL. & TEL. CO. Patented Jan. 15, 1907; Feb. 18, 1908. Other patents pending. Registered U. S. Patent Office."
"The tube herein contained is licensed for amateur and experimental use only, and should not be used in the commercial transmission or reception of messages for pay".
On the brass base, there are patent ## 841396 and 879532.
So, it is not bootleg. The manufacturer, who is very well known, held basic patents on 3-electrode tube design. The issue here is RCA-held patents for the use of tubes in radio and wire transmission and reception, hence the disclaimer about amateur and experimental use.
The O-T-3 carton has this rudimentary data sheet:Stokes records that there were many "bootleg" manufacturers, for whom data sheets may have been a low priority.
"The O-T-3 SILVERTONE tube is a vacuum flash tube for use as an amplifier or detector on a 6-volt storage battery for the filament, and on any dry voltage from 45 to 150 volts, the output gradually rising as the plate voltage is increased.
The current consumption is extremely low, 0.25 of an ampere, and a low temperature, together with a simple and rugged construction, insures long battery life, if the tube is properly handled".
One thing evident here is that O-T-3 was among the first TT filament tubes at the time when high current high temperature pure tungsten filaments were common.
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Actually some capacitance of the pins-socket should be added. (acc. to N. Koren)
about 0.7pF to 1pF to each electrode C.
But that is Dynamic capacitance.
To calculate what max R from generator should be. This Dynamic capacitance, dynamic because it is changing with Amplification factor, creating HP filter with R output resistance of the previous stage as generator.
The more correct, but basically the same is
Cdyn=Cgk + Cgp*(abs(-A)+1)
abs(-A) indicating that the tube is in anode connection with amplification. - sign is indicating the phase shift of -180deg in anode follower.
And this is valid for negative grid biased types.
With positive grid bias A2 class, the formula is slightly different. Because of the other directions of currents in electrodes in these matter.
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Bare in mind that this is only one aspect, but important, for the driver requirements.
Actually the cutoff of the Bandwidth should be -0,25db@20KHz, the same for -0,25db@20Hz
That is -3db@131KHz and 1,6Hz
(It is NOT -3db@20Hz/20KHz)
From that we can see the phase shift as a product. And it is minimal.
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For the LF side, proper C coupling value with Rinput is NOT the only factor. Other factors are C bypass cathode, C in the power supply branch.
AND for inductive loads most important is inductance of choke or primary, that is strongly connected with Internal value of given tube.
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Sorry for the longer post
cheers
A slightly off topic question. In the case of self bias assuming bias resistor is connected to the negative side of filament, how should grid voltage be measured? -4.5v means grid vs. negative side of filament = -4.5v? Or grid vs. middle of filament=-4.5v? Thanks!
With 5 VDC filament, negative side and grid grounded, the actual bias is - 2.5 V. This should be taken into account when applying additional negative bias voltage to the grid.
As an example, the data sheet shows 3 mA at 135 V on plate and -9 V on grid. Under these conditions, the actula grid bias is 2.5 V more negative; it is -11.5 V.
As an example, the data sheet shows 3 mA at 135 V on plate and -9 V on grid. Under these conditions, the actula grid bias is 2.5 V more negative; it is -11.5 V.
I tried increasing the current through an 01A but didn't get the sound I wanted out of it. Into 2a3 outputs the operating point was 122V, -5.6v, 4.5mA. This is a bit over the usual "max" dissipation (not actually stated in the data), 0.55W rather than 0.41W. Sound was very clear with good tone as you'd expect, but it was also thin and lacked body and bass slam. The sound wasn't good enough for me to continue the experiment, so I went back to 10Y and 46 as driver stages. Ale in Bartola valves uses a source follower and gyrator which solves some of these issues with the 01A. Or one can use the 112A which sounds pretty good and is much more of a driver valve. Doesn't have quite the tone of the 01A but more usable.