Finished making the base for the ex-MOD variac, that piece of wood is now on it's third life (having started out as part of a mug tree), had to go out to get some M5 screws as I couldn't find anything to fit here.
In the future I will probably add a box to the output lead with a fuse and fit something lower in value than the 15A fuse I found in the last variac I acquired (which was burnt open circuit by a previous owner/ab-user
).
The other 5340A & an isolation transformer was retrieved from the storage unit.
Some voltage & power consumption checks were done on the working 5340A, power was around 97W, voltage of the red winding of the transformer was around 163V RMS, much closer to the value shown in the book.
I also checked the ripple on the original Sangamo caps and found it was slightly lower than those new Nichicons I fitted to the borked 5340A, that will please Sir re-Cap-A-Lot.
And then I setup the variac & iso-transformer, in place of the suspected faulty 155V winding on the borked 5340A.
Power consumption was much higher at around 140W, the transformer gets quite warm as I noted yesterday, the transformer in the other 5340A stays cool. I think the faulty transformer must have shorted turns.
Output of the +175V regulator is now similar to that shown on the circuit diagram and the RMS voltage near the 135V quoted in the manual (that most voltmeters will show due to the ripple).
We now have a bright display, which stays showing 7s & 9s at the same time, in self check & direct count with no decimal point showing. The high frequency ranges show 0s, I've not tried the inputs yet.
The shorted caps, shorted rectifier and bad 155V transformer winding, make me wonder if someone accidentality, or deliberately run it on 240V mains, with it set for 115V and caused this all this damage.
David