Single Tube 4CX250B Amp For 27Mhz The Build Pt2

[@glbaker5595]

Thanks a lot I appreciate you taking the time to do this. Just perfect project for an old guy stuck in the hills of Kentucky, thanks again

[@uecmitsuimarinedieselengin873]

Hi sir, i would keep tuned and watch your videos like that. Expecting you finishing This project and i would follow you to build an amplifier with those tubes.73 from China

[@وهابالربيعي]

thank you very much for your time ... pls keep on ... regards

[@charlessmith3739]

I’m going to follow this build. Thanks!

[@hotwire5894]

Certainly appreciate your sharing, this is going to be not just a great learning experience but also a lot of fun!

[@spooner454]

I have the transformer out of a pride and the blower, I also have an old military amplifier with two 4cx-250b tubes but the transformer is huge, the box weighs about 120 lbs or so even though the case is heavy aluminum, but it is a six meter amplifier that I think is converted to 11, but I'm not sure how to separate it to be a two piece so I can actually use it, plus it's grounded grid so the output is low the way I understand it

[@kevindrury8390]

Yeah good info.But didn't expect you was going to tear down your tube tester.

[@xavierguzmanjr5495]

Great series - thank you! Are the 3 variants of the tubes pin- and socket-compaitible so the same socket would work for all tubes?

[@radiomedic111]

YES The data sheets will show you the pinouts, just type the tube number followed by the words "data sheets PDF' into google and you will find all of the data sheets for the tubes that I have talked about

[@kevindrury8390]

Why do you like controlling the screen voltage for output power instead of the bias on the grid? Also why a relay on the screen. Is it because when the screen voltage is off the tube is turned off?

[@radiomedic111]

I built my first 4CX250 amp in 1973 and I did it much the way the ARRL handbook showed but trying to use an input "T" network to lower the drive was just too complicated, so I began experimenting with other methods and I come up with the simple reduction in screen voltage that worked perfectly and at first I just used a variac to control the screen transformer because they were fairly low cost but now they are crazy high priced, so then the next step was just a simple voltage divider made with resistors and keeping a minimum of 20 milliamps through the divider string so as to keep the screen voltage fairly constant....the tubes only draw about 5 to 15 Mills. And yes the screen relay is there to shut the tube off in receive, If you look at my schematic you will see that there is always at least 100K ohm resistor to ground and that is for just in case the output control switch ever gets bad contacts and keeps the screen pulled low if that happens. If the screen were to ever become completely disconnected, the screen by virtue of it being in the electron stream would rise all the way to the potential of the plate and would arc over to the control grid.

[@kevindrury8390]

@@radiomedic111 cool thanks

[@cornelishummel7987]

I use olways seperate transformers to regulated en controle the tube better .