Single Tube 4CX250B Amp For 27Mhz The Build Pt6

[@ZUKITHRASH1]

Interesting..thanks for making this build series

[@vacuumfireradio253]

You’re the only person I know of who suggested this method Norman for checking / setting up the input. Brilliantly simple. Well done. Onwards to Pt7.

[@radiomedic111]

Well Thank You but I can not take the credit for using this method....Bill Orr demonstrated it in his article "Custom Design and Construction Techniques For Amplifiers Using the 8877" He did not actually suggest it for grid input in that article but he showed the concept for use in figuring out the Pi output tank circuit and I have used it ever since....I call it "DRY TUNING" because you can tune and load the plate circuit without applying any plate , filament or grid voltage. In that use you would substitute a non inductive resistor of the value of the plate impedance from the plate to ground and if you did not have the tube in the circuit you would then add the value of "C" for the plate shown in the tube specs plus calculated stray "C" across the resistor and when you are done and have found the lowest SWR, you remove the resistor and the cap, connect the tube bring up the high voltage and apply a small amount of drive and you should only need to make a slight tweek to either the plate or load caps and your done......I will show this in an upcoming video and again when I am firing up the amp.

[@radiomedic111]

PS.....I just went and checked out where it was published.....It was in the September issue of QST 1971

[@vacuumfireradio253]

Look forward to seeing that Norman.

[@billcase6015]

Great videos, it's learning this old guy a few things.

[@MM0IMC]

Continuing to watch with interest...

[@hotwire5894]

Thanks for helping me work my old brain, enjoying for sure! you have quite a few good videos, thanks! was wondering if you where going to have a video on the enclosure’s/cabinet ?

[@glbaker5595]

It's a great series it's way over my head but I really want to thank you for at least trying, I have a cobra radio with the upper and lower side band I live way up on top of the mountain so I'm really good as far as altitude and I don't want to run a lot of power but I would like to have a little more modulation for the sideband , I tried to find me one of those old JB modulators one with 1 tube deals but no luck, lot of the old stuff hard to get anymore,what would you suggest if you have time to answer I would really appreciate it, I'm really glad I ran across your side and thanks again for taking the time to try to explain this stuff to us.gl Baker lake Cumberland Kentucky.

[@vacuumfireradio253]

Have a look on FB Marketplace, Ebay and ask your CB buddies. You may find they have something gathering dust under the bench.

[@kevindrury8390]

I guess the pride dx300 would have a 750 ohm resistor because they have two 1500's in parallel in the grid circuit

[@walterathow5988]

is it possible to use a verable resistor so it can be easly tuned for several radios Thanks for making this build series

[@radiomedic111]

No sorry, it is because all variable resistors that can handle the required wattage from the driver are wire wound and that makes them very inductive and that is a bad thing and that would make the input circuit resonant at some oddball frequency and that would show up as SWR.