Well after having started and stopped about a dozen times I am finally back on track with converting my RCA BTA-1S transmitter to 80m. I did have a problem with unbalanced modulation where it appeared on a scope that the top half of the carrier was modulated less than 30% while hitting 100% on the bottom half. Yeah, looked strange to me too. :blink: I found R23 which is a 124 ohm 1% resistor in the 2E26 first AF amp stage was 12+% low. I replaced it and now things look much better.Things still will not hit 100% pos mod but I think I have soft tubes and can live with it for now.All in all it sounds much better than it did when I started.Most of the distortion is gone and all that is left can be attributed to weak modulator tubes.I am feeling better now that I have a decent sounding TX to work with. Next I have to strip the PA section and rebuild it as a regular Pi network with a pair of vacuum variables I have on hand and a coil recycled from the existing output circuit.Not sure what to do about the 6146 RF driver stage yet. I may rebuild it for 80m along with an external VFO or I may eliminate it altogether and drive the 4-400's directly with a few watts of carrier from my DX-60.The latter has more appeal at this point but I may go the VFO route. As a side note I got a fright this afternoon while working on the TX. I had just solved the mod problem and had the tx running a full kilowatt into a dummy load when I turned around to plug in a Harris Solidstatesman audio limiter/amp I planned to used that was sitting on the floor. As I bent over my butt touched the TX cabinet that had a lower access panel removed at the same time I plugged the Harris in. KABANG!! Fire flew out of all the vent holes in the Harris followed by lotsa smoke. I had to change my underwear after that. Amazing what goes through your mind when you have your back turned on 3000 volts. The TX is fine but the limiter amp is toast I believe.So much blackened innerds in so little time. I have no idea whatsoever what happened. It worked fine the last time I used. Maybe caps but that's not all from the looks of things. I think it was actually on fire while I was trying to get the cover off.I started to tell the wife about it and she said "Yeah I heard a loud bang and you yell." I told her it was nice to know that she considered knitting a sweater more important than seeing if I was dead on the basement floor.I figured since she was a nurse she should have at least tried to give me mouth-mouth afterwards.
Now I need to find a new limiter.
I'm making this a sticky post so I can easily find it as I add updates and pictures as the project continues. It will take quite a while to complete.
I'm making this a sticky post so I can easily find it as I add updates and pictures as the project continues. It will take quite a while to complete.