There was one discrepancy that I noticed when comparing the parts list with the schematic. For any restoration, it is worth verifying part values and circuitry - this may save time. It is frustrating when you discover that you missed one or two components, and have to make additional orders. There will be surprises along the way; however, I like to minimize the interruptions and take the time to get a good idea of parts needed. This also helps locating parts.
Modifications pose additional challenges. Manufactures sometimes substitute parts - similar components may look different due to manufacturing changes, or substitution of similar parts from another source. Values may differ slightly - note whether the part is within the stated tolerance requirements of the specific circuit location. Manufactures also make changes after the schematics are printed - there may be additions or deletions to enhance performance, or reduce part count to reduce manufacturing costs.
The other changes are the result of someone trying to fix something. Some well-intentioned modifications may be baffling and sometimes dangerous. I've encountered mods that don't do anything at all!
The Tiny Mystery
When comparing the parts list to the schematic, I couldn't locate C-86 (.01 mfd 20% 600 V molded paper - parts list page 20A) on the schematic. From the schematic, I noticed that C-85 ( .01 mfd, in the AC line primary after S3B, schematic page 19B) was not in the parts list. The values matched, the component type matched, and there were no other lost capacitors, so the mystery was easily solved. Trust me - it isn't always so simple!
Click on each image for a larger view.
That's all!
Next - look for the HP 400L Vacuum Tube Voltmeter restoration.
