The 7A13 is a differential comparator with +-10V internal offset. So you can display a 10V DC signal with 1 mV/div resolution.
Those now too are on my list. ![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif.pagespeed.ce._hfWAz_QHO.gif)
Small correction however, you said 7804 while mine is 7704A
Keep in mind that the 7A13 is full of very Tek specific relays. With a footprint that prevents an easy replacement. Unfortunately they do fail on a regular basis, specially the double contact ones. In the old days they actually repaired them, using a Dremel to open them. I made two test jigs to test them. Seems to help if you connect them to a FG and let them switch a large number of times.
![](http://members.home.nl/baltusg/7A13%20RELAY.JPG)
Tek 7k stuff is addictive. On the bench: 7603 with 7A22, 7A13 and 7B53A. 7623A with 7L5+TG. On cart: 7704A with 7A18, 7S11, 7T11 and 7B70. Then 5 more 7xxx mainframes as spare and a number of parts/fix-up plugins. Like another 7L5 (looking for the big knob assembly), 7A13 without relays (guess why), some more 7A..amps and a number of spare 7B53As. And one self made 7xxx extender cable. About half the mainframes have new PS caps, using adapter pcb's. I had to fix the 7704A a number of times. Bad resistors/arcing in the HV section. Primary bridge rectifier shortened and a shortened tant cap somewhere. Keeps you busy. But all easy fixes.
I have a similar list of TM5xx(x) stuff, next to the regular gear. Yep, I fit in here
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)