Quote:
Originally Posted by Station X
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Adding the insights from that thread, I'm now thinking along the following lines:
My yellow AVO Valve Data Manual (17th edition, 1965) lists the selector switch settings for the E88CC as: 641 237 410 i.e. A1 G1 K1 H H+ A2 G2 K2. I have used a hand lens to confirm these connections inside the valve.
The electrical conditions are given in the AVO book as Vg = -1.2V; Va = 90V; Ia = 15mA; gm = 12.5 mA/V. The Flat Panel conditions are given simply as Va = 100V; gm = 13 mA/V. The 1966/67 Brimar Valve Data Book gives a Vg figure of +9V (!) with the other parameters being the same as in the AVO book - but it does specify a cathode resistor of 680 ohms. Similarly, the data sheet for the CV2493 at
http://www.r-type.org/pdfs/cv2493.pdf states Va = 100V; Vg = +9V; Rk = 680 ohms. Now, at Ia = 15mA, the cathode will be at + 10.2V (V=IR); if the grid is set at +9V, then the grid-cathode potential difference will be -1.2V, as stated in the AVO book.
The E88CC data sheet at
http://www.r-type.org/pdfs/e88cc.pdf confirms the grid voltage of +9V (page 2) but the characteristic curve for Va = 100 (page 8) gives an anode current of 70 mA for this value of grid voltage. With 680 ohms in the cathode, everything will be fine.
All this said, my problem is that I am obtaining similar results from testing on the Flat Panel and on my ‘Dynamic gm tester’, which has clearly labelled rotary switch settings for each electrode / pin combination. Triode number 2 is consistently way down on triode number 1. The actual valves I am testing are CV2493s which are given as equivalent to the E88CC/01. Pin settings for this valve in the AVO Data Book are 741 236 410 i.e. A2 G1 K1 H H+ A1 G2 K2. This arrangement is certainly not what I’m seeing through my hand lens.
Conclusions? I think that adding the 680-ohm cathode resistor into the picture adds some daylight to the data book listings; the AVO 741 switch setting is clearly wrong (for ECC88 / E88CC / CV2439); my measured discrepancies between the two triode sections is due to instability.
However . . . .
Peter G3PIJ