Hello All,
I have almost completed a restoration of a model 60 Cathedral with a "late model" chassis. It matches the schematic on this website "Model 60B late"
I have found problems common to this unit and repaired them including but not limited to- coil primaries open, rebuilt block caps, replaced out of tolerance resistors, cleaned tuning cap, etc. I have aligned it and both bands work. It even sounds good but... I cannot receive stations on the lower end of the AM band. I cannot receive stations from 530 to 650 very well regardless of the signal strength. I live near Chicago, so I have many to choose from. I am using various long wire antennas (45 foot, 90 foot, 22 foot) There is no static between the stations on that part of the band, so I am skeptical of it's performance. All components have been checked and rechecked. Signal tracing from the antenna forward by signal injection checks proper, but I don't know the stage gains. They are not listed on any diagrams. It seems a bit insensitive and not very selective. (Not unlike I was when I was a younger man!)
I anyone has experience with this radio and knows what to expect as far as performance goes, please let me know if this unit normally has an issue with the lower end of the AM band. I want to correct this if this is not normal. Thanks. Ron. radio@radio-americana.com
Hello Ron. ..., generally speaking, I have found the early TRF type circuits leave alot to be desired on all-across the entire AM band reception!! However, the audio quality produced from these old type receivers is Awesome!! Back when TRFs were made, several AM Stations were transmitting at very high wattage levels (all day & night). Some as high as 500kw. Signals from those old Radio Station transmitters could "wake up" a simple-designed AM receiver in those days!! I have many restored TRF radios in my collection, and as much as I enjoy listening to them from time-to-time, the "antenna-feed" longwire antenna designed circuitry was a low-cost way to "link" to the most powerful stations on the airwaves. Down here in Texas, I can receive a VERY few powerful Mexican stations on the low end of my TRF dials, as some of them Mx AM broadcasters are still using over 100kw transmitters. Otherwise, its "hit or miss" using these old TRF receivers. I have also found that even a short 25' outdoor longwire antenna can "overload" some TRFs circuits receiving capabilities!! I have found using a 250 pf mica cap in series with the antenna lead wire really helps sometimes. You might try that, but most old TRF designed radios are "touchy" as a old maid at a "stagg convention"!! Sounds like your TRF radio is working just as well as most from that era to me!? Randal (Txrockr)
Model 60 is a superheterodyne
I'm not too thrilled with the Model 60 sets. They can be capable of decent performance - not fantastic, but decent. It generally requires replacement of all paper and electrolytic capacitors and ALL resistors to achieve this, however. (Hey, that has been my experience. YMMV.)
That said, however, you should be receiving your local Chicago stations on the low end of the AM dial with no problems, assuming you have some sort of antenna on it, even a few feet of wire. When you aligned the set, did you carefully adjust the low end AM padder, "rocking" the tuning condenser as you adjusted? This is critical for best performance, as this adjustment brings the front end in line with the set's IF.
To properly do this, you need to set your signal generator for 600 kc, then tune in the signal. Now adjust the trimmer slightly off one way, and follow the signal by retuning the tuning condenser. If it gets softer, adjust (and tune) in the opposite direction. But if it gets louder (as indicated by your VTVM or oscilloscope), do it again...and keep doing this until the signal does not improve any further. You will reach a point where the signal begins to decrease, and at this point you want to reverse direction and hit that peak again. This is what is meant by "rocking." Afterwards, readjust the high end trimmers for maximum output.
Once you hiit that "peak" on the low end, the dial may not indicate 60. It may be a few kc above or below 60. This is normal.
Gentlemen, thanks for the replies. Yes, it is a superhet as Ron R. mentioned. I have recapped it and repaired the antenna coil primary and replaced all resistors and tubes as necessary. I do know how to align and have gone over this a few times and the results are the same. ( I also know how to "rock" the low freq. padder) The low end of AM band is "insensitive" and does not pick up local 50KW stations very well at all no matter what the antenna length is. Also, stations tend to not be separated very well (bad selectivity) on lower end of AM band. I checked the IF cans for resistance and continuity and they all showed what the mfg. showed to be correct. Not sure where to go from here. I am not satisfied with it's reception. Sound is great. I'm sure it can do better. I have restored many radios in this era and am fairly sure what to expect for performance. Any additional help would be appreciated. Maybe something more advanced for me to check? How do I check the stage gain of the RF? Where is the best place to check the AVC voltage without detuning the RF circuit? What are the stage gains for this radio? None listed in mfg. literature. Thanks for the help. Best to you all. Ron (mccaffrp)
You might try pulling the antenna and oscillator coils, and baking them in an oven for 15 minutes or so, at a temperature not exceeding 180 degrees. Worth a try. Moisture can do strange things to coils...might not help, but then again, it might.
While I have mentioned before that I am not exactly enthusiastic about Model 60 sets in general, I really don't know why you would have trouble receiving a strong local on the low end of the band.
Good luck, Ron.