Dumont RA113 "Burlingame" restoration

[HighHopes]

Hi Bob,

I just reviewed the Dumont RA-113 videos on YouTube. That was quite an experience. I suppose if a set is over-engineered, more things can fail.

On the sets I fiddled with years ago, there was always a coil that would adjust for the audio and video separation that allow one to sync up the tuning. These were sets from the early to mid sixties. Basically it shifted the band where the audio would be fetched from. One tuned the best video and then adjusted the coil for the best audio - no fuss, no muss.

While you were wrestling with the IF strips, I couldn't help but think there was something wrong with the tuner local oscillator alignment(s) which might account for the difficultly in tuning the best video and the best audio at the same spot.

I get confused with the setting of IF frequencies and always run back to AM radio alignment experiences to keep myself straight. In an AM radio, the alignment can be done without using exact frequencies. I seem to remember tuning the local oscillator for 540 KHz (tuning cap closed) on the dial. And then the oscillator trimmer cap for 1600 KHz (tuning cap open). It didn't really matter exactly what the IF frequency was, as long as it was peaked. The point is that things could be approximately on frequency and all was well.

Of course, with old TVs, there are two bands, audio and video which have to be calibrated together. Given the over-engineered nature of that Dumont set, I am wondering if there are two separate mixers, one for video and one for audio. I am wondering if the two slugs that were on the Dumont tuner were for this.

Is this a crazy idea? Two mixers?
Would they allow the IF frequencies to be off a bit as long as the IF strips were tuned accordingly.

Anyway, in all these musing I find myself wondering what exactly is critical in TV alignment, and what really has to be matched to what.

Also, because the audio is FM (wider than AM), maybe the audio IF needs to be stagger tuned as well. Would stagger tuning of the audio IF allow less critical station tuning with respect to audio. Would the bandwidth of the ratio detector accommodate this? I wonder how much of the detector slope is actually used.

Steve