[Music] this is Twi you know we mentioned earlier Bob is not here tonight but don't fret we have some Pine board action for you here nevertheless well I don't actually have a pine board but I've got some splaining to do CU I told you last week uh we mentioned that we'll be talking about the transmitter there and I said I need to talk a little bit about a pinto tube and let's explain how the pinto works before we start explaining the transmitter so that's what I'm going to do tonight I've got some drawings here and I've got some colored markers so I think we're all set to go you know we've talked about the triode before if if you want to learn the basics of how a vacuum tube Works go back and watch ham Nation episode 303 when I talked about a triode and did a you know a basic but thorough explanation of how a tube works and we'll just briefly touch on that here first this is a triode you can see there well we call it a triode because there's basically three elements in it there's a cathode right there uh there's a control grid and there is a plate now there's also uh filament heating that cathode in there we're not counting that as as one of the when we State this as a triode in some cases you know there may not be a cathode the filament itself might be the cathode so let's let's just begin here we put uh some voltage in here at the bottom uh to the filaments we heat that filament up we have the cathode here connected to ground or nearly to ground there might be a little resistance or and you know parallel capacitance in it there but uh the cathode is generally sitting near ground up here on the plate at the top we're putting in a positive voltage uh we call it plate voltage that's a pretty high voltage coming in there um it well in the case of the pine board transmitter it's uh you know I believe between uh 100 and 200 volts currently in the current iteration of that design so we're sitting up here we've got a high positive voltage on the plate we're heating up this cathode down here what's going to happen once that piece of metal gets hot enough right there it's going to start boiling electrons off of this cathode here well those electrons are are going to want to leave that and go somewhere and they look and they see this plate up here at the top and that's a positive voltage where these electrons are negative they're going to start heading in that direction and they're going to jump off that cathod as they're boiled off and head toward the plate because Opposites Attract well what's going to happen there is the thing's just going to run wide open we've got a control grid here between the two though and on this grid we'll put a a smaller voltage um it'll be a negative voltage so we've got a a negative voltage going in here what that's going to do is when the electrons start boiling off they're going to see that negative voltage on that grid and that's going to repel them and they're not going to go through quite so fast headed up toward the plate there or or with quite as much strength now we'll also here on the input we'll put a signal in let's say we put in a a little sine wave there now that's going to cause the grid to swing positive and negative and that's going to sort of Choke off the electron flow or act as a valve to control the electron so when it swings high and swings low the electron flow is turned on and off it's not digital it's you know an analog device so it's going to be uh directly proportional to whatever our input signal is so that basically is an amplifier because we're sending electrons up here to the plate and we're controlling the flow of those electrons with the signal that we're sending into it so that's how a triode works and it's a you know the oldest tube out there so it's uh very much used you know that's um well we talked about it earlier when we were talking about the preamp now let's step it up a notch let's put another grid in there now this is a tetrode we we've got basically the same thing here we've got the filaments we got the cathode we've got the plate uh we've got this control grid here that we put in the bias and our input signal but we've introduced another grid here this is the screen grid now we'll put a little voltage on this screen grid right here a positive voltage as a matter of fact and what that's going to do is as the electrons start boiling off of the cathode [Music] there this green grid here is a little bit closer to the cathode than the plate is to the cathode and it's got a fairly High voltage on it too it's generally a little less voltage than uh the plate voltage but still you know usually a fairly high voltage on it so this kind of gets those electrons flowing with more Gusto when they when they start boiling off of there they see that positive voltage on that screen grid and they're attracted to it uh you know at a little bit uh more strength once they get there they look up here and they say wait a minute there's a higher voltage up here on this plate so they just go on past the screen and hit the plate okay so we get a little more gain out of that tube by having the screen in there because it it just helps improve the electron flow now there's a little flaw with the tetrode here and what that is is you know once we've got the kinetic energy of those electrons being boiled off that cathode headed toward the plate they're going to strike it so hard that some of them are going to bounce back down they're not going to go all the way on out the circuit here they're going to be reflected back toward the screen and that's going to cause a little bit of screen current to flow as well so we're not getting the usage of all these electrons coming off of here some of them are are being wasted they're going back toward the screen well they got to thinking about it and I believe it was uh mullard came up with another tube design the pentode now this is the tube that's being used in the pine board transmitter it's basically the same thing we got before we have the filament that's heating up a cathode we've got the plate up here at the top we've got the control grid we've got the screen grid that we're putting a positive voltage on to and we've got one more Grid in here this grid is called the suppressor grid and if you look here it it's not tied to positive like the screen and the plate uh in this particular case it's tied to ground or it could be uh well it'll be a lower voltage it it won't be anywhere near the screen voltage or the plate voltage uh it's going to be negative compared to those in this case ground is is plenty negative compared to the high voltages there so what's going to happen now as those electrons start leaving down here on the cathode and they're headed up toward the plate they're going to hit that plate real hard because you know they've got the the little extra attraction there that the screen grid got them started heading that direction and they see the plate up there on the high voltage on it they Rush right on past that screen hit the plate now instead of some of those bouncing back like they did before when they try to bounce back they look here and they see this suppressor grid and it's got a negative potential so these electrons being negatively charged they're not going to want to leave that plate and flow toward another negative because you know Opposites Attract so um the same sign would repair so with this being negative here on the suppressor grid those electrons aren't going to be knocked off and reflected back down into the tube they're going to be more focused right on up into the plate there which means we're going to get a a little more gain out of this tube also you know there's a tendency when you've got the electrons reflecting back down in the tube uh with it being pretty high gain with that screen voltage the tube can go into oscillation pretty easy by putting the suppressor Grid in here and having it uh grounded or you know at a negative voltage it changes the inter electrode capacitances of that tube and it's not quite as likely to oscillate so that's another advantage of it uh there are numerous other uh benefits from it and they get a little more complex I just wanted to show you basically what each of these grid is and you know what its function is so Same Old Tube we had before put an input signal in here it's gate it's gating on and off the electrons boiling off that cathode at the rate of the input signal screen voltage here on the screen grid kind of gives them a little kick in the seat of the pants as they're headed toward the plates they're going so hard at this point with so much kinetic energy they jump right past the suppressor grid but any of them that would be potentially reflected back or repelled by the suppressor grid and of course we've got our positive voltage we put on the plate here our signal comes out here we've got to have some way to separate our signal that we're putting in from that high plate voltage there uh the way that uh typically would be done and it's a little more involved in this but uh in the most basic sense we would just have a capacitor coming off of that plate and would get our signal on out here so we don't have that high plate voltage coming to the output where we're trying to connect our next stage to so there you go that is basically how a pentode works and that's a tube that's going to be used in the pine board project transmitter and I believe Bob will be back with us next week we'll be talking more about that it's fairly interesting you know we've already covered the preamp and how all of that worked this is RF this is a little bit different so um stay tuned for that