On some Pentode datasheets (E180F), it says that to turn the triode into a pentode, once should connect G2 to the anode. On others (EF86) it says to connect G2 to the anode, and G3 to the cathode. Does this just mean that on some pentodes G3 is connected to the cathode internally?
Also, even though there is no mention of it in the datasheets, is it a good idea to make the connection fro G2 to the plate via a 100R resistor, even on these small signal pentodes? And, if yes, what wattage does this resistor need to be?
Also, even though there is no mention of it in the datasheets, is it a good idea to make the connection fro G2 to the plate via a 100R resistor, even on these small signal pentodes? And, if yes, what wattage does this resistor need to be?
Yes, many pentodes strap g3 to k internally.
Although it's never stated as an explicit parameter, you will find that pentodes tend to have a fixed ratio of anode to g2 current under normal operation. Typically, small-signal pentodes have a ratio of 4:1. Since your g2 stopper resistor is so small and the current is so low, a carbon type (less inductive) is fine. For a power valve such as KT66, an I2R power calculation might be required to confirm resistor suitability. I've never bothered with g2 stoppers on small-signal valves.
Although it's never stated as an explicit parameter, you will find that pentodes tend to have a fixed ratio of anode to g2 current under normal operation. Typically, small-signal pentodes have a ratio of 4:1. Since your g2 stopper resistor is so small and the current is so low, a carbon type (less inductive) is fine. For a power valve such as KT66, an I2R power calculation might be required to confirm resistor suitability. I've never bothered with g2 stoppers on small-signal valves.
Now that you mentioned about using carbon resistors as gridstoppers because they are less inductive, I want to ask if its their non magnetic nature that is their true benefit. I have actually had metal film picking up fields by nearby cabling and introducing very low level zzz when installed in output valve pins as gridstoppers. Using carbon same value resistors in their place, killed that.
Carbon resistors are less inductive because the bulk resistivity of carbon is higher than that of the metal films (nichrome etc) used for metal film resistors. As a consequence, metal film resistors need more turns of the helix cut between the end caps to achieve a given resistance, and that increases the inductance.
Most resistors have steel end caps and there's no law that says carbon resistors might not have them.
Most resistors have steel end caps and there's no law that says carbon resistors might not have them.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.