Hi om's. I have several Heathkit rigs. They were gifts, with the advice that they did not work just right. I tried to use a couple on the air, but they didn't work or tune right. I like tubes in general, although I have several solid state rigs as well, such as I-coms among others. I liked the Heathkit so much, I decided to buy several more for parts, from ham fest & Ebay, to rebuild one to perfection. While I intended to use one or more for parts, none of them were cheap by any stretch. I decided not to scrap the original two gifted rigs, & progressed to rebuilding the best condition rig acquired from Ebay. Along with the purchase of the rigs, I bought from another ham on Ebay, two said to be new old stock, JAN 6146W, manufactured by Philips ECG, with slightly different date codes, one is 8626 aau, 26th week of 1986, the other is 8652 aax, 52nd week of 1986. While both were sold as new, these tubes have getter flashes, both of which appear to me to have been used, as the flash shows signs of gas absorption in the flash pattern. When I tested them with a dynamic transconductance tester, both readout were 125%. That alone told me something wasn't right. Generally tubes with damaged grids test high on my tester. Tubes that are really good/new always test 100% So onwards to the present, I have finally found the time to restore one of these Heathkits, with the chassis restocked with new high grade caps, & all the mods including the preselect tracking mod for xmit/rec tuning point. I tracked the vfo to a precision, dead on readout across the band, put shields on all of the tubes, & proceeded to install the two ECG 6146 listed above. Right away I knew there was something wrong. The original tubes were a pair of RCA dark cathode types, with no getter flash, telling me they are high vacuum tubes, unlike low vacuum tubes that use a getter flash to absorb the remaining air from the envelope. The AB1 bias point on the RCA's was set by me before swapping tubes, & was very stable over several weeks of testing. When the ECG's were installed, the bias setting was way off, & resetting the bias to the ECG tubes, I could get only about 60% CW power out, or 60 watt, while the RCA's gave me 100 watt output. I also noted a drop in stability. After several seconds, the PO began to drop below 50% or 50 watt CW output. I suspect now, the original owner did not properly dip the plate current during tuneup, & from long winded use, burned up the screen grid, (causing warpage in the focus of the grid) Now comes the questions. The rig was possibly produced 50th week of 1968, stamped in large black ink numbers on the chassis, making it possible the RCA's are the original output tubes, which by the way work great! I also suspect the ECG's are not dark cathodes, due to the tremendous difference in the filament current, between the two odd types. Since there are two filament circuits, some 12v some 6v in series parallel, including bulbs, it crossed my mind the ECG's maybe are not getting hot enough, or back to my first thought, they have the damaged screen grid. My tube tester compensates for different filament currents with a 100 to 130 volt ac adjust, to be set after the tube warms up, by slowly increasing the current, ie; starting from the 130v setting & reducing the setting until the line cal is met in the center of the meter. At this point I have no idea, or guess, weather or not the ECG's are really bad? Now the final question. Does anyone out there know, or have experience with this issue. Is it a circuit mismatch, a damaged pair of tubes, or both? Please reply even if you just have a hunch or guess, I will weigh all comments equally.