Just an update. Got B- shunted and that is working correctly. Also replaced the TR relay and it's working beautifully now. Only had my 817 handy (Watch out now, I don't want to drive this thing too hard!) but it's working! I dialed it into 28.425 since the higher frequencies are where the 4-1000's start showing issues. With 4500v on the plate and all 2.5W of drive, I saw 20w out of it on the bird meter. When times allows, I'll get onto it with something that can actually drive it. (Either the FT-450d or the FT-991 because they're handy) I traced out the grid metering circuit. The diagram shows that it should have been shunted to about 1.2ohm to ground. So I found a 3w 1.5ohm resistor for that task. Didn't see any grid current yet, but I didn't expect it with what little drive.
Nothing when designed for it; the tube is rated to 6000V and runs ~5000V in commercial SW AM and FM BC use. Carl
Tried to tinker a little today on it, but didn't have much time. I did swap over to the 991 to be able to throw a little more fire at it. But my grid metering isn't working, so I'm going to have to track down that issue before I go any further. I did bump up to about 25w input and saw 200w out on 10m. I yanked the meter out of circuit and ran it through my multimeter just to test and saw about 25-30ma of grid current. But progress is progress I guess.
Thats what makes this all fun! My first KW amp was made from a pair of sorry looking BC-610's and other parts from Army MARS when I was in HS and had it done at 17. I was banned by my parents from using it on 10 and 15 but it had OK TVI suppression for the lower bands. Wound up with a pair of 250TH's modulated by 810's. RF and audio driven by a Viking I and this was at the peak of Cycle 19. That started a lifetime of working with amps for hamming, commercial, BC, and military.....almost 60 years. Carl
I figured out what the problem is with grid current monitoring. I just duplicated the wiring from the SK. He mistakenly had grid current metering through pin 2, instead of 3. So I'll pull all the wiring out and reroute everything. I know pins 2 and 4 in the 1K tube share a common ground, so that explains why there was no meter movement. I'll get that squared away tomorrow. Then I think I'll be ready to start testing it more for output power and certainly more drive.
I swapped everything around, the grid meter is working now. It's a weston 301 300ma meter, 20ma FS. I used four 100ohm resistors to net a 25ohm resistor that I put in series. (24.8ohm in series showed full deflection with a 300ma load.) Only problem now is that it certainly isn't putting out the same power as it was before. I'm wondering if I need to revise the metering circuit. The documentation stated that they spec'd it with a 1ma FS meter in place. I'm wondering if I'm pulling ground too high for #3. Maybe I need to step back and rethink it. Resistor shunt perhaps? Swap over to a 1ma FS meter?
I went ahead and ordered a 0.1 ohm 3w resistor as a shunt. That will give the grid a nearly close to ground potential. Then I'll use a pot in series with the meter to fine tune it.
I tinkered for about 5 mins with it today. Just jumpered the meter straight across. Went from 20w in/30w out to 20w in/200w out. So it's the meter causing the issue.
