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I see the Eico sweeper marker generator has a crystal in it. What is it's resonant frequency?
The marker frequencies for the traps were 19.75, 21.25 and 27.25MHz. The bandpass markers that are most important are 22.1, 24.5 and 25.75MHz. The Eico could use the one or perhaps two or three crystals to calibrate it's variable frequency generator.
A cheap shortwave receiver with digital readout could be used to calibrate the marker. The marker accuracy needs to be roughly +/-10kHz particularly with the sound IF and sound traps vs the video carrier 45% position on the slope of the video IF response. The 27.25MHz traps must be fairly accurately set as they will affect the overall IF response. The 19.75MHz traps accuracy is least important.
Historical sidenote affecting the design of the 1948 thru 1952 receivers. This was the time of the TV station construction freeze. 1948 coincided with the sunspot peak and it played havoc with RF reception. Co-channel and adjacent channel interference between stations beyond the RF horizon created headaches for FCC planners. The double upper and lower adjacent channel traps were RCA's answer to alleviate the problem at the time. I recall the summer of 1972 the interference with another sunspot peak. From Toronto Canada reception, KMOX channel 4 in St Louis totally obliterated WBEN channel 4 Buffalo. KDKA channel 2 Pittsburgh would override EGR channel 2 Buffalo. I had an RCA 8T243 (the same chassis as yours which I still have more than 50 years later) and it worked better in these summers than many newer sets. Having more traps was a brilliant idea but it makes alignment more difficult.
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