Discussion in 'Amplitude Modulation' started by KA4KOE, Apr 21, 2017.
Mr. Bauer went outside of spec on the mod Vsg as well. It's wayyyyyy high.
Here is the portion of the schematic showing the HI/LO power scheme.
Voltage on the screen grid is no problem, high current is.
Is the TX working well?
That value has to be a typo and should be 750V instead of 950V and here is the reason:
Looking at the annotated schematic, there is only 750 volts supplying the Mod screens through 470 ohm resistors.
The voltage drop across R73 or R74 at the 1kW power setting for zero modulation is 0 volts, so the actual voltage at the screens during zero modulation would be 750 volts. At Max. modulation the voltage drop across R73 or R74 = 13 volts, so the actual voltage at the screens during max modulation would be 737 volts.
I'm going to have to kill B+ to the driver during receive as it is wanting to oscillate (TPTG). Unless there is a better way to do this.....
Also, it is working but I am doing proofing, familiarization, etc. Grid current is much improved and actually adequate at low power. Did some carrier transmit tests into the antenna (brief) and it seems to work much better than on this knock-off "cantenna" from DX Engineering.
So V3 is oscillating without V1 or V2 in the circuit?
If the RF is not killed during KeyUp, the V3 driver is just going to amplify whatever is given to it.
I'm likely going to put in a second relay to kill B+ during receive to the driver.
Also, need to re-analyze the tank. Plate current goes way high on high power. Q may be too high and the different values throw it too far off resonance??? Or my connections, which work well on low power, cause issues on high. We'll see.
OK, I've run the numbers. My tank, as is, is setup for a Q of 15. This is too high. I've read that a Q of 12 is ideal. I've plugged in the taps for Brother Bill's conversion trying to reverse-injuneer a known working design. The coils look like Johnson 48 uH units, 46 turns each. Using my handy dandy Q and D spreadsheet, Bill's Bauer is set up for a Q of 10 at 12 turns tapped, give or take.
Additionally, I am going to yank out this bulkhead coaxial connection on the side of the Bauer and hard-wire to the coax directly. Let's go ahead and eliminate a potential problem spot right there. Yes, yes, yes, I know you guys told me to s***-can the bulkhead connector awhile back, but I'm hard-headed and impulsive.