Why You Shouldn't measure HV on a multi-meter

Unfortunately this was my favorite meter. I was measuring the secondaries on a United Transformer Corporation CG-301 (round can). I thought the highest tap on there was 475v, from what I found online. Apparently it has one thats over 1500v too! My meter read 1500-something and then ZAP! (I taped the probes to 1' PVC tubes so I didn't have my hands near it HI - WEIRD stuff, even a couple hunderd volts).

More Amp ideas

I have been working on the calculations for the tank. I calculated my Tune capacitance range - roughly 10-500pf for 1.8-54mHz. I used an equation I found on AG6K's website (part 5 of "Amplifiers").

After looking at the Handbook for additional information regarding tank circuit calculations I see the equation I used is the same. However, there are two different systems for calculating the rest of the values - those with respect to a Pi network and a Pi-L network.

I want a Pi-L on the output for better harmonics/IMD supression, so thats what I am going to work on here.

The Handbook gives two different schematics for a Pi-L. One has a Pi circuit going to Rm (Image Impedance) followed by an L. The other one is your standard Pi-L - a Pi followed by an L, where your R2 is the output (50 ohms). This is getting kind of confusing because the calculations are all based off the first one with respect to Rm = 300ohms. They say that the L in the first example transforms Rm to R2. Thats a lot of number twisting!

I guess where I am hung up now is why in the world they would plug in 300ohms for Rm when the output impedance needs to be ~50ohms to match to the coax? I suppose if you were loading 300ohm ladder line that would be one situation where 300ohms would be needed.

Another note is all exact values in this are THEORETICAL. Once I get the circuit together things are bound to be different - stray capacitance with component locations, extra resistance in the inductors, etc. With so many unknowns I will surely be doing some tweaking on this once it is together.

Anyway, more number crunching to come.

If you have or know where I can get a couple decent vacuum variables - 5-500pf or 10-500pf @5-10kv, and another up to 1000-1200pf @5-10kv let me know!

I also thought about doing a 5-250 on the input with a 250 doorknob in series for the low bands.

Update - Ive been busy!

I got my tube for the amp project in the mail yesterday - a GS-35b. It is a bit bigger than I expected and it is really heavy. Its one thing to look at dimensions and plans, but when you actually hold it in your hands its a bit different HI. This thing dwarfs an 8877 (although, the 8877 is a better/more powerful tube).





The speaker box is not done yet. I have the majority of the wiring/electronics done, but it still needs some more work. The panel is in the works. This cardboard mock-up is nice because I can play with the location of all the controls. I put all but the filter controls on and then soldered the wires in place. That way I knew how much wire I needed for them. I added just a bit of length to a few of them for some room to play. The volume control (brass in the middle) will need to move a bit as the knob for that is a lot bigger. The pots with the knobs on them are for the filter, those are just the ones that came with it for now. All of the knobs I will use are machined out of aluminum.



There is a TON of wiring on this thing.



I modified my original plan. I was originally going to have 4 mono/2 stereo inputs with the monos configured (for the rigs) to where I could route all to both speakers or any combination of the 4 to one speaker for dual monitoring. When I got in to the wiring it was a lot more complicated than I originally had planned because the filter unit needs to also be switched in on any of those 4 mono inputs. Long story short, I changed it to 6 mono inputs individually selectable/filterable. There are also 3 stereo channels now also - one on the front panel.

Things left to do - finnish the mock-up of the front panel, do the rear panel, build my VU input meter, finnish the knobs, mount the circuit boards, and once the panel designs are done work on the printing for the metal plates.