Well, my waiting paid off. I picked up a Tektronix 4052 along with a Tek 4631 hard copy unit and custom metal cabinet late last year from a guy selling surplus medical school equipment. The 4052 had three missing keycaps and that was very difficult to remedy, but found an ex-Tek employee who had the keycaps I needed! Also a bunch of program tapes and several ROM cartridges. I now have the Character Set ROM and Signal Processing #2. The 4631 had paper too old to use but I found some on the internet for $10! Also, after about a dozen printouts, the main drive belt fell apart. Even with the service manual, finding a replacement was very difficult. Fortunately the service manual listed the number of teeth and length of the belt, so I was able to get one from Stock Drive Products. I also located the service manuals and found a 4662 multipen plotter on EBAY. I revived many of my old 4051 programs from the '70s, except for the ones that use the CALL "EXEC" command :( including my music playing program in 6800 assembly language. I even modified a Kraft PC joystick to plug into the 4052 joystick connector - works great, played one of the startrek games for the 4051 that supported the joystick. I also found and won a 4054 on EBAY early this year! This machine had been auctioned from Caltech. This machine was listed as not working. After some cleaning, I decided to try unplugging and reseating all the chips in sockets. I found one of the 16K bit DRAMs was bad, bought a 64Kbyte set to upgrade the memory to the 128KByte maximum and got the machine running again! Then I tracked down a malfunctioning opamp in the tape drive board and loaded some of my revived programs. Wow - the 19" direct view screen is incredible compared to the 12" flat CRT screen in the 4051/52. Although it is not flat, it has much more detail - I can see why it was preferred for CAD. Amazing how Tektronix had the higher resolution completely compatible with the old software. The 4631 hard copy made an incredible printout. Spurred on by the article at computergarage.org on using 4051s in Battlestar Galactica, I decided to try to write a short program to display a squadron of Battlestar Galactica Vipers on patrol. Using the image in the computergarage article, I printed the image on my inkjet, wrote a short digitizer program for the plotter and used the 4052 to digitize the outline of the viper in the picture. This is saved in a single array, then using Tek graphics WINDOW and VIEWPORT commands I draw the array with a single DRAW command, move the origin, resize the window and draw again. The same display on the 4054 is noticeably sharper than the 4052. By changing the DRAW command to a PLOT command, I'm able to plot the program to the 4662 - that's what I loved about the Tek PLOT 50 language. I'm still looking for someone with information on the CALL "EXEC" command and the 'newer' 4052/54 bitslice machines. Philip Belben was correct about the increased speed - some of my 4051 benchmarks run 10X faster on the 4052 and 4054. The "A" rev 4052A and 4054A added a TI GPIB chip to increase the GPIB speed further, and added a couple of other commands. The 4054 added a "refresh cursor" that could be controlled with the built-in thumbwheels in the keyboard. There was an Option for REFRESHED GRAPHICS that expanded on that concept and added an 8X300 coprocessor board with refresh graphics memory to have a whole graphics image be drawn without "storing" the image on the screen. Apparently my machine left the factory with that option - but the board is no longer there. Love to hear from someone that had that option board. Monty McGraw