Well I think I can call the Heathkit C3U done, all that was really wrong with it was the dreaded Selenium rectifier was still in situ, so that had to go, all the caps in it were tested on my other cap testers and were found to be in good shape, only 2 electrolytic caps in the whole thing, all others where either Mica or polyester, but all were checked out. Switches were dirty so a good dousing with Servisol cured those and also the pots, checked the resistors and voltage divider chain on the range switches miles off, as was a 470K on the power factor switch and 2 x 1Ms on the magic eye socket, so replacements were ordered.
When they were delivered by supplier in person this afternoon, I set about removing the old ones. What bastard job that was and while doing it, I came to the conclusion that each case where they had drifted, was where ever they were mounted with others sharing the same tags/connections. I thought they drifted as a result of excessive heat travelling up the lead from the soldering process, so replacements were given more space (plenty in the case so no problem). All went well until I realised I had ordered resistors to suit the American version, so I cobbled some together from my RS sale win to approximate the missing values
but it all worked within 0.3k so thats OK.
Removing the old selenium rectifier from its tubular sleeve came next and was replaced with a IN4007 and 20K 1/2 watt resistor in series, all stuffed back in the tube from the old rectifier for protection with decent airflow through it. The HT only draws 3.5mA so 1/2 watt is heaps big enough for the dropper. Now the B+ is up from 114V to a respectable 145V and the open circuit leakage voltage readings are 5V = 7.5V, 25v = 36V, 150V = 110V, 250V = 190V and 450V = 370V. According notes on the web from others who have gone through the similar restorations, this is normal for these testers. The actual current flowing through the voltage divider chain is minimal and when testing a capacitor for leakage the voltage collapses to almost zero and slowly builds up again so there not much of a chance to blow a cap by giving it too many volts because the test switch is sprung loaded and has to be held in the test position and if the magic eye does not close instantly and open very quickly then the cap is leaky and is to be thrown away and that is determined in about 3 seconds so the cap never sees the full voltage.
Tomorrow I'll give the case a clean up and it joins my bench as a permanent part of my test gear. It was originally considered as a doer upper and flipping again to fund other purchases, but not now, its managed to impress me
The 470k here was 490k
was replaced.
the 1Megs here were replaced
The voltage divider as it was
As it is now with plenty of space to apply heat sink to the leads while soldering and also the botch to make it UK spec.
The IN4007 and 20k are inside the original tube from the Selenium rectifier.
A view of the chassis from below, nothing in it really.
Here is the view from above (this is not my photo, its a photo from the web) as you can see, there is plenty of space.
Here it is testing a 22k resistor.
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