545/Repairs

Fan mounts

See also the general article on Fan mounts .

Ken Chorney says:

Just wanted to add an alternative supplier for replacement fan mounts for the Tektronix 545 oscilloscope fan. Digi-Key currently stocks two part numbers which fit and work perfectly: RPC1597-ND and EAR1345-ND. Both are 1/2" length (same as original) and both have 8-32 male threaded ends (same as original). Both are slightly smaller in diameter (0.4" vs. the 0.5" originals) but this does not affect their fit at all and likely does not affect their function appreciably. I have installed three of the RPC1597-ND standoffs in my 545 and they fit and work perfectly.

Vertical Amp Fuse

Late-production 545A (S/N 29960) adds F1054 to protect the termination network in case a vertical amp output is shorted to ground. (Also any instrument fitted with Mod Kit 040-227.) If the fuse opens, all fourteen 6DK6's will draw the usual current, but through the screen grid instead of the plate. A long time ago someone (Stan Griffiths?) worried this would fry them. I did the math. The 130mA combined screen current drags it down to 220V which is 35V above cathode which inputs 0.35W of heat which is safe. However, the 5W R1218 will see 17W and fry, and then 6DJ8's V1033/V1043 will fry trying to pass 130mA to the 6DK6 control grids. Unless you turn off the power within about ten seconds, which you probably would do since you're the one who shorted it poking around and you know you did it. So, just the fuse.

Add a note inside: TURN OFF POWER IMMEDIATELY IF VERTICAL AMP IS GROUNDED EVEN BRIEFLY

If you don't think that's enough, upgrade R1218 to 15W. Ohmite TUW15 ($1) or B20 ($7). Then the instrument will survive open F1054 indefinitely. (It won't work, but it won't eat itself either.)

These mods can be retrofitted to any 541/543/545/541A/543A/545A/551/555.