So I built, for larger signals, a new probe and made an analog meter from a 50 microamp movement I found on Amazon.
I modded the new probe to be less sensitive, which means it can measure much larger signals, but it does not read directly in volts and had to be calibrated with an accurate signal generator.




I did this last weekend and tested it yesterday. I can switch the probe over to the digital meter and measure WEAK signals or connect it to this box and measure LARGE signals. But again, even on the digital meter, 1 volt of RF reads on the digital meter as 180mv or .18 volt. This is because, again, I built it to be less sensitive so: A) It can take more voltage and B) It loads (or disrupts) the circuit it is measuring a LOT less than the other one.

GOOD NEWS/BAD NEWS:So the analog meter works wonders. I'v verified my 6au6 amp is KILLING IT. 120mv in, 1.5volts out into a capacitor that was feeding a dead short on the filter. I will get a lot more when feeding a good load.

Unfortunately, the input pin on the crystal filter is grounded/shorted. This is a new development in the last few weeks. I KNOW that filter worked not even three weeks ago. I will not object to the eBay seller, as it was working and this is a 40 year old part (more like 45-50 years, really, as that product was discontinued in 1976 or 77.)
I went on a "Vintage Heathkit Repair" page. Found out a shorted input pin happens a lot and often, disassembly of the filter clears the short but so far, no one has figured out what is going on.

It's a sealed, soldered together unit and not easy to take apart. I found another one on eBay for $23 including shipping. Not sure which way I want to go but at least I can measure RF voltages easier now, I know my amp works, I know why my measurements have not made a lot of sense and the transmitter is working other than the filter has now failed (after 40+ years, we can expect failures with these old parts).

EDIT: I will probably just buy another filter as the seller is now offering the one above for $19 including shipping.

So, a step forward with a step back - still, I am super proud of my 6AU6 tube amp (with a 45 year old NOS tube I paid $9 for) as I designed it myself and it WORKS. I know I have too little signal coming out of the filter (I mean when I get the new filter in) but a second 6AU6 stage will get me up to the 2 volt or 5 volt level the mixer needs (it wants 2 or 5 depending on which grid of the mixer tube I feed it to).

Im learning a lot (and re-learning as I knew tube theory really well as a teen ager). Honestly, this is the most Ham Radio fun I've had since the 1970s.