Vacuum Tubes: Episode 5 - The Pentode

[@edgeeffect]

I love how you have a semiconductor busk/boost converter on the same breadboard as a pair of pentodes.... it's like it's 2015 and 1965 at the same time. :)

[@edgeeffect]

I've read about tetrodes and pentodes "A MILLION TIMES" and never quite grasped what all the "blah blibby blah" is going on about. But after listening to your excellent intro here, I finally get what the screen grid and suppressor grid are all about. :) :) :)

[@TastyBusiness]

Vacuum tubes are starting to make alot more sense now, thank you!

[@mixedproduce9787]

The sal kahn of vacuum tubes! Great stuff

[@Pollys13a]

Thanks so much, for doing these videos, very clearly explained and easy to understand, enjoying them a lot :)

[@UsagiElectric]

Thank you so much for the praise! I'm glad you're enjoying the videos!

[@cobar5342]

Great video, thank you

[@richardatanacio4049]

Vivid explanations...thanx for sharing this info.

[@UsagiElectric]

Thank you for checking the video out!

[@adrianobueno6984]

Amazing explanation, thanks!

[@travishein]

Interesting. attaching screen and grid to the plate! I never thought of trying this.

[@UsagiElectric]

Thanks for watching! And, yup, by connecting the suppressor grid and screen grid to the plate, you essentially end up with a triode that has an oddly shaped plate. But, it drastically changes the characteristics of the tube and you can take a pentode that normally has a sharp cutoff and make it react like a triode with a much more linear response. This is a pretty good resource on the different ways you can hook up a pentode as a triode: www.audiodesignguide.com/New2A3/ETF06TS.pdf

[@armitage64]

Enjoyed the instrumented testing! Would be cool to see the difference between tetrode and triode mode on the scope using a high frequency input.

[@UsagiElectric]

That's actually in the works! I've got an old HP signal generator in the garage that needs a bit of restoration, so once we clean that up, I want to use it to see how fast we can push the tubes before they start running into issues.

[@Electronzap]

That is really cool that people are selling grab bags of vacuum tubes.

[@UsagiElectric]

There's a surprising amount of good deals for random tubes showing up on eBay and other places. Keep in mind, the tubes aren't necessarily desirable tubes, especially within in the audio community, but for playing around and building random circuits, it's perfect!

[@edgeeffect]

One of the great things about hobby-engineering is that there's always a good supply of nerds around to buy your old garbage. :) In my own lab, I have an extensive collection of "other people's garbage" ;)

[@tomsworkshop5856]

Thanks for this. I'm no longer scared that 829b tubes can't be used in triode mode.

[@lunaroja4703]

Increíble que quedó más claro como era el funcionamiento del pentodo.

[@UsagiElectric]

Thank you, I'm glad you liked the video!

[@DonnyHooterHoot]

I just got 50 NOS 1t4's for less than a buck a piece. I have a 7 tube AM radio that uses ALL 1t4. Gonna play!

[@georgegonzalez2476]

Back in the 1990's there were government surplus auctions, mostly from some huge govt warehouses in Utah. Where there would be like 12,000 brand-new 6SK7's (for WW2 radios) and 6AC7's (from WW2 radar sets). I think she winning bids were very low, like $400 a lot. Kinda surprising as their associated equipment was mostly EOL by 1955. The 6AC7 might be usable as a 6AU6 work-alike. Needs more like 30 volts to pull 10 milliamps but perhaps good enough.

[@coldfinger459sub0]

Just came across your channel on my endeavors of teaching myself about vacuum tubes after a couple years of watching videos. I need videos like these to teach myself how to design and build my own equipment . Following old books and manuals and videos..

[@JenkinsUSA]

Excellent 💯

[@MyNathanking]

Excuse me, Usagi Electric, but isn't this the same thing you said about the tetrode? What's the difference betweeen a tetrode and a pentode?

[@deathkeys1]

Hello, I just started playing woth tubes myself, I got some 6jt8 (the cheapest I could find) it is a pentode triode, I tried several configurations (using just the pentode, I didn't messed with the triode yet) I tried with 150v, 46v even 18v on triode condiguration I manage to cunduc, but I never get above 0.4mA(yes, 400 microamps) I do have to ask, why? How? Am I doing anything wrong or is it how it was supposed to My set up was like this Supressor grid(internally connected to the cathode) Screen grid (connected to positive through a 22k resistor, tried 10k and 33k no noticiable chamges) Cathode connected to GND as per standard Anode ( load, a led(no resistor going an ammeter ) Control grid, a 100k potentiometer in a voltage divider to allow up to 5v Any help is appreciated. Something strange is that the tube never fully goes off, it never stops conducting even when the control grid is maxed out.

[@emilehobo]

When you note +24 V, does that mean you connect the negative pole of a 24V battery to the plate?

[@UsagiElectric]

My power supply is setup with the positive of the 24V supply hooked up to the plate, then the negative of the 24V supply hooked up to ground. To get -12V I hook the positive of my 12V supply up to ground and then use the negative of the 12V supply to get my negative voltage. Essentially just like explained here: forum.digikey.com/t/get-a-positive-and-negative-voltage-output-from-power-supply/10593

[@emilehobo]

@@UsagiElectric Thank you for your honest answer. May I recommend you always draw the full circuit, including the power supply as to avoid confusion? I understand people now even say that labeling the ground as negative is okay, but according to science it’s actually positive.

[@arthurjean-luc8040]

bonjour j ai une question je voudrais faire une alimentation 2000 volt avec une gi7b et comme commande un 2c39

[@UsagiElectric]

Hmm, both the GI7B and 2C39 are transmitter tubes it seems, so I’m not sure how well suited to power supply operation they would be. I’m really unfamiliar with transmitter tubes. But, the GI7B looks like it should be able to do about 170mA at 2kV, which is quite a lot of power. Of course, how you build the supply will depend mostly on the type of transformer you have. For 2kV, you’ll need about 1.5kV RMS. With a big enough transformer, that should be possible. Otherwise, you’ll need to go with a flyback design. The best thing I can suggest is to look at old oscilloscope schematics and see how they generated the HV for the CRTs, there’s a lot of excellent designs floating around there! Google Translate: Hmm, les GI7B et 2C39 sont des tubes émetteurs, semble-t-il, donc je ne sais pas à quel point ils seraient bien adaptés au fonctionnement de l'alimentation. Je ne suis vraiment pas familier avec les tubes émetteurs. Mais, le GI7B semble pouvoir faire environ 170mA à 2kV, ce qui est beaucoup de puissance. Bien sûr, la façon dont vous construisez l'alimentation dépendra principalement du type de transformateur dont vous disposez. Pour 2kV, vous aurez besoin d'environ 1,5kV RMS. Avec un transformateur assez gros, cela devrait être possible. Sinon, vous devrez opter pour une conception flyback. La meilleure chose que je puisse suggérer est de regarder les anciens schémas d'oscilloscope et de voir comment ils ont généré le HV pour les CRT, il y a beaucoup d'excellentes conceptions qui flottent là-bas !

[@kasel1979krettnach]

why does look your setup tidy and mine is taped together :(

[@UsagiElectric]

Haha, don't worry, it's a mess just outside of the camera shot!

[@dc9582]

Thanks for your videos, I am trying to learn and use some valves for a little project myself and i found your videos very useful. Can I ask you how and what you used to be able to plug the valves on the breadboard? thank you.

[@UsagiElectric]

Thank you so much! That's awesome to hear that my videos are helpful! To plug them into the breadboard, I just use a standard "belton" style tube socket that I salvaged out of some old electronics, solder on some 22 AWG wire to each of the connectors, and then bend the wire so that the pins end up in a line. Here's a closer photo of the socket: i.postimg.cc/kMW72bcr/IMAG3143.jpg Bent like that, it works out really well with pin 1 being on the left and pin 7/9 being on the right. I would say you could probably get away with about up to 100VDC through a breadboard and this connector if you're being careful, but I'm not sure I'd recommend it, haha.

[@dc9582]

@@UsagiElectric sorry about my silence... Busy days, thanks a lot again for all the info.

[@GTS00000]

Can you recommend some current literature on vacuum tube theory?

[@frankowalker4662]

Over here in the U.K. they only sell small quantities of valves on ebay, (up to 5), at an inflated price. :(

[@UsagiElectric]

Yeah, I've gotten pretty lucky in finding nice large lots for affordable prices on eBay. I think currently I have around 500 6AU6 tubes in my possession, which should be enough for most of the tube microprocessor project I'm working on!

[@frankowalker4662]

@@UsagiElectric Cool, Looking forward to seeing the full build.

[@hendriknommeots2342]

@ 8:00, probably would be nice to have a bonus episode about kinkless tetrodes, since you give quite nice explanations :D en.wikipedia.org/wiki/Beam_tetrode

[@UsagiElectric]

Thank you so much! I was actually just thinking about that last night as I finished up editing the next episode about the heptode (which goes up tonight!). Unfortunately, I don't have a good beam tetrode tube in my collection to experiment with on the breadboard. One of these days I'll get my hands on one and we'll see what we can do at 24V though!

[@avonfonds2567]

thank you i didn't know pentode can be converted into triode i believe only few pentodes can do this

[@boonedockjourneyman7979]

I got 11 banker box loads of tubes for $100. Had to pick them up in person. Now what? How about an episode about testers. Those will cost $1K.

[@alanpecherer5705]

Frankly, I'd rather buzz around in the sweet looking Austin Healy you have in your garage rather than to screw around with 6AU6's.

[@pnpplpnppl]

Ah! Now I understand why you have a zillion 6AU6s

[@MechanicForGMCCars]

I have problems with small circuets those wacum tubes realy look easy to operate I wish you made circuets for controling transformers and their different aplications. Im working as mechanic It anoy's me to no end the old GM 4 pin ignition modules do not have advance ore retard option and circuets do not exist for controling ignition coil polarity change,or pulse duration control,or phase control for multi tap transformers or useing varizse electricity out come in different stages like plasma or amplifier combinations . So I realy wuld like to see those experiments and actualy I am curriuse to see what that wuld do to ignition coils. Again anoying small circuets that no one understands and comonli those are not marked or do not have circuet diagrams . So those wacum tubes are indead promesing devices .

[@NepaliAngusYoung]

Adapter

[@NepaliAngusYoung]

Diagnos computer card