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Plate Resistance
On Thu, 3 Jun 2010 12:08:42 -0700 (PDT), walt wrote:
Data from Terman’s example on Page 449 of Radio Engineers Handbook: (1) Eb = DC Source Voltage = 1000 v. From your own data Eb = DC Source Voltage = 800 v. (2) Emin = Eb - EL = 1000 - 850 = 150 v. [See Terman, Figs 76(a) & 76(b)] You do not supply context for me to apply to your data. (3) Idc = DC Plate Current = 75.l ma. 0.0751a. Idc = 260mA (4) EL = Eb - Emin = 1000 -150 = 850 v. = Peak Fundamental AC Plate Voltage You do not supply your minimum nor maximum plate voltage swing. (5) I1 = Peak Fundamental AC Plate Current = 132.7 ma. 0.1327 a. You do not supply your peak AC Plate current. (6) Pin = Eb x Idc = DC lnput Power = l000 x O.0751 = 75.l w. Pin = 208W (7) Pout (Eb - Emin)/2 = ELI1/2 = Output Power Delivered to RL = [(1000 -150) x 0.1327]/2 = 56.4 w. You report Pout, but we cannot use this formula for lack of data. Pout = 100W (8) Pd = Pin - Pout = Power Dissipated in Dissipative Plate Resistance Rpd = 18.7 w, From your report of Pin and Pout: Pd = 108W (9) Rpd = 18.7W/0.0751^2 = Dissipative Plate Resistance Rpd = 3315.6 ohms From what is reported by you: Rpd = 108W/(.260mA)˛ Rpd = 1597 Ohms (10) RL = (Eb - Emin)/I1 = EL/I1 = Load Resistance = 850/0.137 = 6405 Ohms (6400 in Terman) You do not report Emin but you report Load Resistance RL = 50 Ohms (11) Plate Efficiency = Pout x 100/Pin = 56.4 x 100/75.1 = 75.1% Plate Efficiency = 48% By all reckoning according to your reference from Terman, using what you report, it appears that you have exhibited a Conjugate basis Z match as you claim, and that the plate Rpd by the same reckoning is the same as we formerly arrived at Rp. It would appear that over the course of some dozen years between publications that Terman simplified the term Rpd to Rp which, according to you, is not found in your volume, and as such this migration of terms seems logical by the numbers agreeing in both volumes for different labels. Inasmuch as Rpd does not appear in Terman's later work, nor in any of the Tube specifications since that era, Rpd appears to be an orphan. You report your own Rp (now Rpd) or its equivalent by resistor substitution (a valid determination) to be on order of 1400 Ohms. This conforms closely to the value found above, and the data reported by RCA for Rp in a design of similar characteristics. The range of possible values taken from RCA: 900 Ohms to 1500 Ohms. Taking your low, the high from my range, and the higher computed through your supplied data using Terman's formula, the average is 1500 Ohms with a variation of roughly 6% which is about the limits of superlative accuracy for conventional bench equipment. What this means is that all three values are identical on the basis of accumulation of error. Having said that, this is not the end of analysis. However, at the first pass your data has demonstrated that the Plate serves as a real resistor dissipating half of the available power being supplied to a load that is conjugately matched. The only difference is that you state as much, but dismiss the plate dissipation as being a real resistor. Perhaps I mis-state you. If not, I take issue with that and ask once again, as this perception is unique to your hypothesis, do you have data that differentiates the resistance of steel absorbing and dissipating the impact of the electron stream as being different from carbon absorbing and dissipating the impact of the electron stream? Would it serve to replace the steel plate with a graphite one like the 845 (similar to the GM-70)? When I review the spec sheets for this tube, it reports an Rp of 1700 Ohms - hardly remarkable at 100 more Ohms than the computation above. Of course, there are compounding application differences, but still, graphite plates or steel don't seem to force a new conclusion. Materials don't seem to be an issue. Certainly the mechanisms of resistance differ in the kinetics of speed, but not in the product of heat. To my knowledge, no authority bases the concept of resistance upon the speed of the electron, but rather in the kinetics of its collision. 73's Richard Clark, KB7QHC |
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