Webcor - Initial Electrical Evaluation

I've finished an initial cleaning of the upper mechanical tape transport circus, so I'm moving on to the electrical bits. Once the electrical bits have been revived, I'll return to the motors, springs, and levers for adjustment.

Vintage electronics, in this case from 1952, have components that don't age well - powering them up after decades of storage is not a good idea!

There are 13 wax-covered capacitors that must be replaced, as they no longer work as intended - they often can turn into resistors, short out, or have radically different values. This can cause extensive damage to other components, including fire, and shock hazards! 

🚒🧨🎆🧯💣

Don't plug these things in until a thorough evaluation and replacement have been done. There are also several old Bumble Bee capacitors - they have black bodies with a number of color coded stripes - these must be replaced as well. Other components will be checked for any signs of heat stress, cracking, or bulging.

Some of the wax paper capacitors that will be replaced....

All of the capacitors and sketchy looking parts will be located on the schematic, which was found inside the case. Then, an initial parts order will be made.

Sometimes, manufacturing changes will vary from a supplied schematic. Component values may change, parts deleted, or additional parts may appear 😃

I have worked on gear that people have 'modified' - deleting or improperly replacing parts with things that are ridiculously dangerous 💀, pointless, and some that don't do anything at all! 😂

Here's my typical secret process - been doing this for a few decades 🤓

Usually, I like to concentrate on one type of component. In this case, the capacitors. I chose the easiest one to start with 😜

This is an example of a wax paper multi-section capacitor - C14A, 14B, and 14C, three caps in one package. There are four leads - one that is common to all three sections, and then seperate leads for section A, B, and C. The color code and values are listed on the cap - sometimes hard to read, although easy enough to compare to the schematic for verification.

The highlighted areas show how each section is wired into the circuit. It is important to note that the actual wiring isn't as always straight forward as the neat schematic would suggest. In this case, wires from 14A and 14C both connect to the socket for the 6X5 tube - only 14A is actually part of that tube circuit 😄

It is common for tubes to have unused pins - so in this case, the wire for 14C goes to 6X5's unused pin 4, where the two resistors are tied - see the red circle above. This is a common trick to ease wiring and keep leads short - avoiding unwanted effects that may be caused by long leads.

The circled component is resistor R27 - with a value of 4700 Ω, 1Watt. Take a close look....

This is tied directly to capacitor 14C. Note the very dark color of the middle part - the body should be brown, like the top end. The value is indicated by the color bands - which should be, from the bottom, yellow, violet, and red. Without a schematic, you'd have to guess the value, as the red band is charred. The top silver band indicates a value tolerance of 10%. This resistor and cap are part of the rectifier tube circuit, which supplies the power to the whole mess - and over time, this part was getting baked - possibly due to the filter cap leaking and on the way to failure, or something 'downstream' has failed, and drawing more current than normal. To be determined 😁

And finally, something a bit silly to finish....

The resistor issue is easy to explain... the frog, not so much.

Now, off to creating the initial parts order - there is always some component that is overlooked 🙄

Next post, typical soldering procedure for C14 - A, B, and C 😄