Excerpted from postings on The Philco Phorum, December 2005
by Ron Ramirez
As you restore your Model 80, 81, 84, or 37-84, here’s one more thing you should do. There is a 4 meg resistor inside the I.F. can, mounted on top of the I.F. transformer. Replace this with a new 2 meg, 1/2 watt resistor.
The easiest (and probably safest) way to replace it is to clip the leads from the original dogbone 4 meg resistor right up against the body of the old resistor. Wrap the leads of the new resistor around the leads of the old dogbone, and solder into place. This helps avoid the possibility of damaging your I.F. transformer by trying to remove the old dogbone leads (been there, done that).
Remember, if you want to really extract the best performance from these sets, replace ALL carbon resistors as well as all of the paper and electrolytic capacitors. The old dogbone resistors, especially in these sets, tend to be way off-tolerance; and Model 80 receivers respond especially well to new resistors in place of off-tolerance units.
Why change from 4 meg to 2 meg? It has been my experience that in these type of detector circuits, using a grid leak higher than 2 meg results in lower volume. A grid leak resistance of 2 meg seems to be the “sweet spot” for peak performance (and loudest volume). Your mileage may vary.
The purpose of making these changes is to extract the best possible performance from these admittedly limited 4-tube regenerative sets. By following these instructions as well as those given in the related “Model 80 Performance Modifications” service tip will result in a performance improvement that may very well surprise you as to the capabilities of these little sets.