It seems like people have many different definations of "Hi-Fi" (or maybe it's just me), so that why I use quotes. Of course the name comes from high fidelity, in audio terms meaning high sound quality. You might say quality is in the ear of the beholder, how good is good? Well, this pages reflects my definetion, basicly any amp with a good quality output tube, or better yet tubes, and a good speaker or speakers (or a way to attach an external one) fits my loose defination of Hi-Fi. In the earily days radios were made bigger and better with nicer speakers and more tubes, and at the same time electronic phono pickups and FM radio allowed better source material. This section is dedicated to those amps, radio, and record players that were more than just simple 5 tube table radios and little portable record players.
I'm not sure if this was typical of other manufactures, but this is my experience with various 40s vintage Westinghouse radios so far. In the earily days of series string filament radios, 150 mA heater tubes (50L6, 35W4, etc) were still new, and in some cases, not even available yet. These sets usually used 6V tubes as commonly seen on transformer sets, except for the output and rectifier tubes, which were usually a 25L6 and 25W5 or similar. This of course gave you a series string that didn't add up to nearly 120V, and a large resistor was used to drop the voltage. What Westinghouse did on a number of sets was to add a second 25L6 in series making the radio a push-pull output instead of a single tube seen in the common AA5-type sets. This put the extra voltage to better use, and was a simple way to get a push-pull output as it's not as easily done with 150mA tubes. My first example of one of these sets is a H-122A that belonged to my grandparents. I later found that many models used this same bakelite case but were sold with a variety of record changers housed in a wooden "consolette", giving the owner both a small movable radio as well as a console for record listening. This might explain the use of a nicer output section when compaired to the other common table radios of the day, as this set was designed to compete with lower end consoles. There were also version of this chassis in wooden sets, and maybe many others I don't know about. The following list is of Westinghouse models that look to be similar to my H-122A. Unfortunatly I'm finding a few schematics here, a few pictures there, so I'm still trying to make sence of it all. On the following list, models that do *not* use the push-pull output circuit described above are marked with an X (and will be removed should I later find they don't have a chassis of the same form-factor), those that look to have a similar circuit are marked with a *. A double * indicated the same chassis number as the H-122A. Here's the list so far:
H-104B X H-105B X H-107B X H-108B X H-110B X H-111B X H-122 ** H-122A ** H-130 ** H-137B X H-153 * H-138B X H-155 * H-156 * H-157 (similar circuit, different chassis) H-171 H-184 H-247 (same case as H-122A)I can't say for sure if the list is accurate, or if there were similar chassis used with different numbers. I'm currently working on a H-130 set so once I get it working, I can give an update as to how it compairs to the typical AA5 set.
As a side note, I recently bought the remains of a set with a very similar chassis, a V-2127 if memory serves. It actually looks like it's a plain old 5 tube set with two 25L6s in parallel, why I don't really know. If anyone has any clues for me, please let me know. Keep your eyes open for such a beast, if I get any answers, I'll post them here.
Want a nice HiFi radio but stuck with an cheap AA5 set? Unfortunatly it's taken me some time to figure this out, but there are a few simple changes that can be done to an otherwise typical AA5 set to improve fidelity. The components themselves (tubes, resistors, caps) aren't so much a limiting factor as the circuit, which typically was intended for low cost and limited frequency range. The first thing that came to mind when attempting to improve sound quality is the speaker. I've been surprised at how good some of the old speakers sound, especially for their small size. Some experimentation might be needed to see if a different speaker will help sound quality or not. Just keep in mind that typically size will be limited and cabinets aren't designed with sound quality in mind, so keep your expectations within reason. I discovered, after a little reading about radio troubleshooting, that there are high frequency harmonics generated by the output amplifier, which are usually eliminated by the use of a cap across the primary side of the output transformer. This can be seen here. This schematic shows a .02 uF cap used for this purpose. This is all great, but unfortunatly the bigger that cap is, the lower the frequency that bypasses the output transformer. I've used .004 uF caps in a couple different sets, in place of a .02 there was a very notable improvement in high frequency, in place of a .01 there was still better frequency response. I'm not sure if there would be any issues with using a cap that's too small, allowing harmonics through the radio's output.
Another idea that I like is the use of feedback to improve fidelity. I don't need to reinvent the wheel, this is already well described here. The only comment that I have is this: I like the idea of using the old secondary windings of the transformer vs. trying to add my own, just because it seems easier :) Given that, I'm faced with the issue of having to add a seperate diode for the detector (see description on above site). I elected to use a 1N34A diode on a couple sets instead of swapping tubes, just because it required fewer modification to the set. I still need to do the finishing touches before I know how the feedback circuit will work out.
To make my already loose defination of HiFi a little looser, some radios use a simple 5 tube design, but have larger speakers or nicer cabinets that give a little better sound. I've started using an RCA 9-X-561 radio with my 45 changer, both are the same vintage and made by RCA, so it seemed like a good fit at the time. There are a couple other models with different cases but basically the same chassis, one is the 9-X-571, the other I will add once I find the model number. These all have a large 8" speaker mounted in the front of the case, and seem to have quite good fidelity, for a table radio, despite the simple 50L6 output tube. I also have a large Zenith which is basicly the same idea. My poking around eBay has turned up few others, though I'm sure they're out there, it's often hard to tell what's inside the case from a picture and poor description.
