I like working on transformerless radios for the same reason: no worries about power transformers, many of which are very difficult to find today for vintage radios. I have three transformerless vintage sets in my collection right now -- all Zenith: H511, MJ1035, C845. I don't know if the MJ1035 counts as a "transformerless" set, since it uses a filament transformer wired in parallel with two series filament strings; however, the B+ is derived from the AC line.
I also have a question about filter caps. My Zenith MJ-1035 has a very loud 60-Hz AC hum which I am sure is caused by the 3-section power supply filter capacitor going sour (if it is, it wouldn't surprise me since this radio is 45 years old). Would it be possible or practical to replace just the "guts" of the original filter cap with modern, smaller caps? I know you're doing just that with your Air Castle set, but I'm wondering if it is even cost-effective to undertake the same project on a much newer radio. Also, I wonder just how I'm going to be able to get at the terminals on the 3-section filter, as they seem to be blocked by at least one layer of underchassis wiring. I have visions of having to disconnect dozens of wires, components and such just to get to the capacitor. Of course, if I can work from the top of the chassis and remove the capacitor's innards at that level (leaving the underchassis wiring as it is), it will make the repair a lot easier.
BTW, I know all too well what you mean regarding working on radios with problems. I like working on those as well, but when the problem is
very difficult to find, then the job starts grating on me. My Zenith MJ1035 is a case in point. The radio works extremely well from an RF sensitivity standpoint, as it will pull in stations for miles around using just a 6-foot length of wire on the antenna terminal. However, the audio is extremely weak, and I think the volume control may be open. I can tell the radio is pulling in signals, as the stereo FM indicator light illuminates on just about every station the set picks up (most of the FM stations in my area, 35 miles from downtown Cleveland, broadcast in stereo).
I haven't done much with the radio lately, but I might power it up later today to see if it is still working at the level I just described. I notice that the case of the volume control is supposed to be grounded (such a ground is shown on the schematic diagram), but on my set the ground is missing; therefore, my first step in eliminating the loud hum I mentioned will be to re-establish that connection. It wouldn't surprise me if that eliminated or at least minimized the hum. I'd like to avoid doing anything with the filter cap unless it is absolutely necessary because, as I mentioned, it is likely to be a very involved and messy job with all that wiring directly in front of the terminals, looking directly at the bottom of the chassis. I can't help wondering what Zenith's R&D guys had in mind when they designed the MJ1035 this way--did they think the filter would probably last at least 50 years (!), so they made it darn near impossible to replace if or when the cap goes bad? After all, we VKers know it is more a question of when, rather than if, a filter cap will fail, especially in very old equipment. If Zenith's R&D boys thought the filer caps in these radios would last forever, they were very sadly mistaken, although I haven't read much here in this forum regarding replacement of filter capacitors in any of Zenith's high-end tube radios of the 1940s-'60s, including the MJ1035. Were the caps in Zenith's higher-end sets meant to last years or decades longer than those in the company's cheaper sets, including small AA5 table models? I'm asking this because my Zenith H511, now 59 years old (!), is still working very well and still has its original 3-section filter cap--no noticeable hum yet. Were the caps better made 60 years ago than they were by the 1960s? Another example: My late grandmother had a Sears Silvertone table model radio made in 1936. The radio, long gone by now, still worked well 40 years later, with its original filter caps. The only thing wrong with it, and I mean the
only thing, was that the power cord was bad and needed to be replaced, as the insulation was crumbling and there were bare spots, making the cord a safety hazard. The set was unceremoniously discarded shortly after my grandmother died, and the cottage the radio was in (her summer getaway) was sold; the new owner of the place obviously didn't know or care beans about antique or vintage radios or even had the germ of an idea how much that particular radio would have been worth today.
However, again I wonder. Were capacitors made to last decades in the '30s?
If so, their quality has really taken a nosedive in the last seventy-plus years, as the small filter caps and other underrated components used in today's electronic devices often go bad within a year or two, if they last that long.