Friday, July 24, 2020

The cap divider tube amp performance

Last night I put a headphone on the amp and fed it with a antenna through a diode I received signals. Without the diode all is quite. For the test I used a tapped coil. I could move the tap and receive different stations. This would be a good amp for a hollow state version of the 40/80.

Using the cap divider powered tube amp as the AF stage
of this receiver would be a cool and interesting project.
 It could use a lambda
diode oscillator or a tube oscillator.

Thursday, July 23, 2020

Ground to ground???

Joe had a dead battery and Tom offered to help. When they connected the jumper cable one had a bad end and it fell off. Joe says "Oh man!". Tom says "Not to worry". Tom connects one end to his battery and the other to Joe's battery. He pulls up to Joe's car until the bumpers touch. Boom Flash Spark. Tom backs up and look closer. He had connected his end of the cable to the hot terminal and the other to Joe's grounded terminal. When the bumpers touched BOOM! He moved the lead on Joe's battery and all was well when he touched the bumpers again.

This is the same as having two chassis on your work bench with the power lines grounded on one and hot on the other.

Always check a chassis to ground before betting your life on the circuit being wired correctly.

Use polarized plugs to prevent injury.

The schematic for the amp using the cap divider to power the tube heater

The as built schematic except one resistor. I put a 470 Ohm resistor in series with the diode to avoid inrush on power up.
I ran the sim to see how it would compare to the actual circuit. 
A tip of the hat to the DIT. A very useful circuit indeed.
One caution if you try it.
Use a polarized plug and be sure not to ground the hot line.

Wednesday, July 22, 2020

Cap divider part 3 proof of concept

DIT produced a winner with the Cap Divider. I put it on a breadboard and the results were impressive.

The datasheet offered this circuit. I used 1.5k cathode resistor and 100k for the rest and .5ufd caps throughout.

I put a meter on the input and output. The signal generator on the input.

I adjusted the input to 10mv.

Apply power and have 10 volts output. Looks like a winner.
I used a PI filter in the DC supply I will draw it and post next time if my internet does not crash. My server is not doing well this week I keep timing out.

Sunday, July 19, 2020

The cap divider revisted part 2

I took 6 .5ufd caps in parallel to replace the 5ufd cap and bingo! 12.56 volts feeding the heater. The tube has a nice warm cherry glow. It is a big advantage having a junk box with a bag of .5ufd high voltage caps in it.
This was the circuit from my last post. I used the parallel lamp to bypass some current around the tube. After replacing the 5ufd cap withe the 3.3ufd cluster I removed the lamp.
Note the B+ is 120vdc in sim. The real circuit reads 170vdc. Why?

 Anywho, I know have a dual triode with heater glowing and a 170vdc B+ so what to do with it?

The datasheet gives info on building an amp.

Saturday, July 18, 2020

The cap divider revisted

The DIT did good with the capacitive  divider. It had over 400 views and counting. I pieced together a little board with one powering a tube. I have some motor run caps in my shop. I had a 5ufd and a 7.5ufd on hand. I need a smaller cap but I made do for the test board.
This is the tube I'm using. It requires .15 amp. A 3ufd cap would be better but I have a 5ufd. I put a pilot light across the tube heater to share the current.
This ceiling fan cap would be ideal for testing the circuits. You can parallel the sections and have 1.5 ufd, 2.5ufd or 4ufd.
Here is my as built.With 120vac @60hz I read 12.7 vac across the heater. The lamp is a safety indicator. When it is glowing I am reminded to watch where I put my hands. I put a diode and 15ufd cap in series across the input terminal and have a 150 vdc supply. I will build the circuit in sim and post it.

Thursday, July 2, 2020

Earbud driver using a mosfet output stage

It is not pretty but it sings. I put a drop of glue where the part was located on the schematic and attached the parts. Then it was just a matter of connecting the dots with a piece of wire.

50uv input gives 800ua output. My eadbud is rated 1ma so that is enough. With 100uv input the signal distorts and will act as a "plate detector" receiving AM.

I changed some capacitor values for the build. This is the response for my build. I can add a 12" test lead to the input and receive my local AM station.

 This could be my new favorite. It does need a receiver built to feed it.