Looking at the listed data sheets for D3a by , Philips, Telefunken and Siemens, all give short data for triode operation with grid voltage of +10Vdc. Yet they don't show that area on the curves. Just wondering if anyone knows what the original idea for application was there.
Thanks
Thanks
Interesting observation that I have not noticed before. But the 24 ma current and 470 Ohm cathode resistor listed for that operating condition provides a bias of 11.28 Vdc at the cathode, meaning that with +10 Vdc on grid 1 the net is -1.28 Vdc on grid 1.
Why the datasheet was done in this manner and what the original application was remain good questions.
Why the datasheet was done in this manner and what the original application was remain good questions.
Very high-gm valves tend to suffer more from grid current and therefore bias drift. With late generation high-gm valves it was not uncommon to recommend an 'oversized' bias resistor, and then to compensate with some positive grid voltage, so you end up with a normal bias point but greater DC stability. If you didn't do that, you would have to use a low-value grid leak resistor instead, which is obviously a problem if you need high input impedance.
Got it , thanks. I'd known about that for larger, more 'industrial' pass tubes, 6528 , 6336 where data sheets advise use of cathode resistor no less than a given value (to net % of total bias V), but with the much greater current this positive bias/high value of Rk arrangement wouldn't be practical. I didn't make the connection. Thanks for tying the two together.
It's also a reminder to care about Rg value when using LED bias on tubes like these.
Thanks
It's also a reminder to care about Rg value when using LED bias on tubes like these.
Thanks