Quote:
Originally Posted by Reece
The noise problem in the building is one thing, but an AA5 can often do amazingly for DX at night if it's tuned up right. If you recap that little Zenith and max tweak the IF's, it should be easily able to pick up WWL New Orleans 870 Kc at night, and WSB Atlanta 750 Kc. Try it near a window and turn it about to aim the loop antenna. If it doesn't have an X type safety cap install one going from the cold side of the power switch to the other side of the line. That will often cut a lot of the noise carried by the power line.
|
I looked at the schematic for my H511-Y and found a small capacitor connected between one side of the AC switch and the plate of the 35W4 rectifier tube, which is probably the safety cap you are referring to. I'm sure this cap will need to be replaced along with every other wax capacitor in the radio, as this set is over 60 years old (made in 1951). Probably no wonder I'm getting interference from TV horizontal oscillators and other assorted noises at random spots on the radio dial. The loudspeaker is not in its best shape, either; the cone is torn in several places, but probably salvageable (as suggested to me by another VK member whose name escapes me at the moment). Even at that, the radio still sounds good, but since most AM radio stations these days are talk or news and talk the condition of the speaker doesn't matter much.
BTW:One thing I've been wondering about for the longest time is why Zenith used a special non-inductive type of electrolytic filter capacitor in the H511 series of table radios. If this cap needs to be replaced at any time, Zenith states (on the schematic) that the capacitor must be replaced with the same type as originally found in the radio, or else, if the cap is replaced with a standard one, a special circuit (shown in dashed lines on the diagram) must be installed. I wonder why Zenith chose to use a non-inductive type of electrolytic in these radios, rather than an ordinary, garden-variety 3-section one. What is/was so special about the design of these radios as to require the use of a non-inductive main power supply filter capacitor?
I realize the H511 series was one of Zenith's best small table radios in the early to mid 1950s, but to use a special (and likely unavailable except on special order) filter capacitor in the B+ power supply doesn't make a lot of sense to me.
As to tweaking the IF transformers, I'll have to leave those alone since they require a special tuning tool (Zenith 68-19), which is probably no longer available. I couldn't do anything with those transformers even if I had the alignment wrench, since I do not have an RF signal generator.
I am amazed at the simplicity of the circuitry in the H511 series; the schematic takes only one page, at least in the Riders schematic series (the Sams Photofact folder for this set probably has a much larger diagram). This is probably because these are simple 5-tube (AA5) radios with the same basic circuitry as has been used in such radios since they were introduced in the 1940s or '50s.
The only difference I can see in the H511s (commonly known as Zenith's "Consol-Tone" and/or "racetrack" sets and housed in rather large oblong-shaped cabinets) is the tone- and volume-compensation circuits in the audio stage (a hallmark of this series), either between the 1st audio stage and the output tube or between the output tube and the speaker. Some of these radios used a small 3- or 4-lead encapsulated printed circuit component in the audio output to perform the audio shaping task. My H511 doesn't have this part (I've looked high and low in and under the chassis trying to find it), but probably uses discrete components to achieve the same results.