Original circa 1970 capacitors.
After building the AC-1 clone, I kept on the lookout for an R-5 or R-5A receiver. Finally, one popped for sale from an estate of a silent key and radio collector. It was listed as "not working, parts only" and had been in storage for an unknown length of time. Being a relatively simple receiver, I hoped it was within my abilities to get running again. From the amount of dust, it must have been in storage a fair number of years. I should have taken a photo before cleaning the PCB.
Here are manuals for the R-5 and R-5A:
Original circa 1970 capacitors.
Notice the bulge and rupture on the tan end at about the 1 o'clock
position.
After a couple hours of careful desoldering and replacing, the new capacitors were in.
New capacitors on top of PCB, including two under speaker.
New capacitor on bottom of PCB.
The schematic called for 250uF capacitors, but 220's were used in the original. I replaced based on what the schematic called for. Re-alignment is needed in any case due to component tolerances, but this absolutely guaranteed it. The schematics provided a detailed step by step procedure for alignment, and surprised me by calling for an EIA standard dummy antenna. Out of curiosity, I plotted Spice simulations of the EIA antenna against straight impedances of 50, 70, and 300 ohms. Curves show Vout/Vin (dB) where Vin is the signal at antenna input and Vout output of the R-5A low pass filter. The significant loss is due mostly to the antenna model, not the receiver's low pass filter.
The EIA is similar to a 300 ohm impedance antenna. For alignment, a tv balun for 75-300 ohm would probably work well enough, as would resistors of around 250 ohms. After another couple hours of aligning, the receiver was ready for use with the AC-1!