Some VTVM porn for you.
I have finished sorting out the Heathkit V7-AU. I've done a naughty thing and put the 1M resistor usually in the probe inside the unit. I've replaced the 4mm sockets (one of the old ones disintegrated when I was soldering), filter cap, rectifier diode. You can basically now use it as a normal multimeter albeit negative is always at earth which is not a major restriction really. The original 1/4" jack is preserved so I can whack my RF probe into it. I need to adjust the resistor on that however yet. Peak internal voltage is 169.4 volts which is fine.
I am VERY surprised this electrolytic didn't explode at all. Plessey were notorious for producing crap capacitors. I think the previous owner was drunk when they installed that diode.
![](https://i.imgur.com/G9kK7I4.jpg)
New cap and rectifier. Vishay/BC this time:
![](https://i.imgur.com/Tl0Fpxl.jpg)
Modifications and new 4mm sockets. The red wire is added between the + terminal and the 1/4" socket tip. There is a 1W Vishay/Dale 1M 1% resistor between the tip and the DC input wafer.
![](https://i.imgur.com/7U3wFle.jpg)
Calibration is complete and it's spot on with DC volts, no sign of instability. AC volts is good too. Resistance is reading a tiny bit high on my test set (small pile of 0.1% RN55D's - resistance standard = £1.50!) so I'll check the divider resistors at some point. I'm not all that bothered though for now.
Now I'm bored. Back to eBay for more TEA!
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif.pagespeed.ce._hfWAz_QHO.gif)
Edit: For ref yes I'm aware there is a hazard if you plug something into the DC socket and leave AC probe in on high voltage. This is not dumbass proof but it requires the least amount of modification to it
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)