[Joeztech]

In a Philco 41-280, -286, -287 or -290 radio chassis the 1st IF transformer at the plate of the 1st Detector (mixer) the schematic appears to show an adjustable ferrite core in the primary with a fixed capacitor value, while its secondary that drives the 1st IF amplifier grid has an adjustable trimmer capacitor. I am working on cleaning up the Rider's schematic for these units for a friend and just need to know for sure if I am interpreting the schematic correctly.

Some of you have probably worked on one of these and knows the answer.

Thanks in advance.

Joe

[Arran]

 I have a Canadian Philco model 42 which is similar to a 41-280, and one of the IF cans does have a threaded rod sticking out of the top for a permeable slug, but it also has at least one trimmer in the same can. So if the schematic shows this on the 1st IF can then it is probably correct for the 41-280-290 as well. If I remember correctly these sets have three If cans and two IF amplifier tubes as well, I was told that this was necessary with the set that used the XXD mixer-oscillator triodes (or sets using the twin triode XXD/14AF7) because the detector side offered less gain then either an octode or pentagrid convertor in the front end. It was also a way of delivering more gain and selectivity, with fewer parts, and a cheaper price then having a proper tuned RF amplifier stage.
Regards
Arran

[Joeztech]

Arran;

Thanks for that response. The schematic does seem to indicate that there is an adjustable ferrite slug present. It shows the adjustable trimmer capacitor on the secondary feeding the grid of the 1st IF amplifier tube. Your set appears to match the indicated circuit on this schematic.

I have a Philco 40-201 I restored and it is somewhat similar, in that it uses a broadly tuned RF amplifier (1232 pentode) followed by a 7J7 mixer-oscillator. The 1st IF transformer in it has two ferrite adjustable slugs plus a tertiary winding feeding the suppressor grid of the 7B7 1st IF amplifier tube. So my 40-201 has some significant differences, but similarities at the same time. It appears to be another design to incorporate higher selectivity in the IF circuitry. Philco began to use the broadly tuned RF amplifier on many models for a number of years.

Joe

[Arran]

Joe;
  I've seen that trick that they used in your 40-201 used in a few radios, such as in a Canadian RCA Victor A-30, in a Fada model 1001 that I own. What is interesting is that the A-30 also has five bands with this broad tuned RF amp, but it's larger brother the A-22 has six bands, and a tuned RF amplifier stage, and a magic eye. I have electrically restored both the A-30 and the A-22 and can't really figure out why they would use a tuned RF amplifier stage in one set but not the other, I haven't really noticed much difference in performance, though maybe it helps on short wave for selectivity? There is one model below the A-30 that I have yet to own, it's called an A-24, it has four bands rather then the five of the A-30, but the same broad tuned RF amplifier stage of the A-30, also six tubes, and all three sets that I mentioned have a pushbutton bank of six buttons. Oddly enough there does not appear to be a table version of an A-30 (or A-37 for the following year) and no console version of an A-24, but there is of the A-22 and A-23, product planning in the radio industry was strange.
Regards
Arran

[Joeztech]

Arran;

Before the advent of the superhet design, there were lots of tuned radio frequency radios (TRF). Those had multiple RF amplifiers, each with its own tuned circuitry in order to have adequate selectivity. Selectivity is more of an issue when tuning a weak station next to a strong station. The selectivity helps to keep the strong station from wiping out the weak signal station. Philco had some high end radios in the middle to late 1930s that even had IF circuits with adjustable selectivity. RF sensitivity is more of an issue on shortwave bands, especially the higher frequencies. On the AM broadcast band not much sensitivity is really needed. I have a Hallicrafters SX-25 which has two 6SK7 RF amplifier circuits. On the AM broadcast band one RF amplifier stage is not used. A 4-gang tuning capacitor is used along with a 4-gang fine tuning capacitor. It has two IF amplifier stages with switchable extra coils in the IF transformers plus a crystal filter for CW and voice only reception. It does do a better job of receiving shortwave stations than the Philco 40-201, but then it is not a broad-band radio with the best audio frequency response. The 40-201 has limited use on shortwave bands as its tuning is coarse and very touchy on the highest shortwave band.

It is interesting to see the variations in design offered by various companies during the 1930s and 1940s. A significant number of people were keeping up with foreign news due to events leading up to WWII. After WWII interest in shortwave broadcasting dropped off. Consequently the number of sets offering shortwave reception declined.

Joe

[Arran]

Joe;
  Most of what I am speaking of are Canadian market RCA models, usually built in Canada. I've noticed that there seems to have been a greater interest in shortwave reception in the Canadian market, for a longer period of time, then there was in the U.S. Even in the early 1940s most U.S manufacturers seemed to have been pairing down the number of models with short wave, and how much band coverage they had, whilst on the Canadian sets all but the cheapest models had at least one shortwave band, the RCA A-23/CGE KL500 were both five tube sets but had four bands.
   This may explain why Philco Products of Canada Ltd. produced slightly modified versions of the Philco Tropic line for sale on the Canadian market, particularly the ones with four or more bands. But for some reason whilst very few post war U.S models offered multiple short wave bands, and most of those died out around 1948, they were offering multi band house sets in Canada up until the mid 1950s, later if you could the import models like rebadged Graetz (RCA) or Phillips sets. Then you have the peculiar situation with the Canadian equivalent of a 49-905/50-925, the U.S sets have an FM band, the Canadian sets don't have FM but have a shortwave band and say "Tropic" on the dial, it isn't that there were no FM stations in Canada but for some reason this is what they did.
Regards
Arran

[Ron Ramirez]

Sarnoff et al were very effective in suppressing the adoption of FM; so much so that it wasn't until the 1970s that FM really started to take off nationwide here in the US. Up until then, FM was mostly the home of easy listening "beautiful" music and classical music.

My parents had a large Sears Silvertone AM-FM table model radio when I was a kid in Kansas City; I do not remember the model number. I do recall switching it over to FM as a child and finding KFMU 94.9 ("FM 95", they called themselves), and only a few other, weaker stations. As I recall, the stations I found were either beautiful/mood music (KFMU) or classical. I didn't leave it on there long - I switched back to AM and WHB, then KC's leading rocker.

Yes, there were a few FM radio stations here and there which began programming popular music, "progressive" rock, etc. in the late 1960s, but it wasn't until the 1970s that popular music, country music, etc. began a mass migration from AM to FM and never looked back. Unfortunately, when rock and country took over the FM band, classical and easy listening/mood music died out on the band for the most part.

I know KFMU switched call letters to KCEZ in the 1970s, and are now KCMO-FM, their original call letters, playing classic hits, I believe. KCMike could confirm if he sees this thread.

Armstrong would be pleased to know that his FM system finally won out, but it took far too long to do so. Were it not for the negative campaign against FM run by Sarnoff and his minions, FM probably would have been accepted much earlier. And who knows what might have happened to AM?

[KCMike]

Yes KCMO-FM is oldies format. But they seem to play the same ...maybe 30 or 40 songs over and over.
Far as classical, I can only find one station out of Lawrence KS. A public radio station that plays classical part time in mornings and evenings, rest of time is talk. Thank goodness I have an am transmitter to pick what I want to hear via the computer.

[Joeztech]

After the move of popular music to FM, many stations now compete for being the loudest and boomiest on the band. Audio on those stations is so bad that it is almost unlistenable. Overmodulation and overcompression is the rule of the day. I have some expensive high end FM tuners, but if jazz and classical music disappear from the FM band in my area they will become useless to me. I may have to invest in a low power FM stereo modulator and feed audio from CDs into it in order to have anything worth listening to on FM. Such is the state of culture and radio these days.

Joe

[Ron Ramirez]

Joe

If I didn't have my EDM xmtr and a dedicated laptop playing a rotation of almost 900 easy listening/mood music tunes, my FM receivers would also be useless. All I can pick up around here is about 70% country crap and 30% rock - or, I should say, what passes for "rock" these days. Jazz? Nonexistent around here. One Mexican station. A few college stations; one or two play classical music sometimes. There is a classical station in Louisville but I am outside their coverage area; therefore I can only receive them on the one receiver connected to an attic antenna.