Possible to convert 42MC-50MC FM?

[vintagecollect]

Hello,

I usually don't post in this forum. I recently bought a 42MC-50MC FM tuner only radio w/ hopes to some how to low key modify it to get something in the 88 to 108 fm current band, possible? I really want to use this other than a display piece, any ideas, simple to complex please.

[bgadow]

I am pretty sure I read an article about this in the last year or so, in the MAARC newsletter Radio Age. I'll see if I can find it.

[bob91343]

It's basically simple but the devil may be in the details.

1. Change the local oscillator range.
2. Change the resonant frequency range of the rf stage.

These things may be possible just by modifying coils. And there is the minor detail of recalibrating the dial.

[vintagecollect]

I'll post some pics later, 1941 brewster set, older restore, just a display piece. They used an fm modulator or special transmitter to use this?? Fully operational. I'm interested in the minimum mods to keep original as possible, also to put back to original if later desired. Thanks for input!!!

[vintagecollect]

Found the info, Thanks!!!



now I have to order info. thanks for tip on radio age.

[vintagecollect]

Found really good plans that include parts list, schematic, atricle w/ alignment info!! Seems easy, made for 14 to 30$ well done, one of the articles I was looking for.



linky:


http://www.somerset.net/arm/fm_only_...converter.html


has anyone used any of these? please posts, show your sets too!!
will post pics when get a chance.

[wa2ise]

I have this Wmweson prewar AM/FM set, and I use a modified ham radio block converter intended for 2M to 6M conversion (144 to 50MHz). Changed it to do 100MHz to 45MHz.

Another method that did not work out well was to use an old cable TV descrambler box to tune in a 6Mhz section of the 100Mhz FM broadcast band (cable channels 95 to 98 or so(, and to grab the box's tuner's IF output and feed that to the prewar FM set. But reception was rather noisy, suspect that the box's local oscillator has lots of PLL phase noise, which translates to added crud on teh FM signal. It doesn't bother TV sets as most use intercarrier FM IF strips (the phase noise is the same on the picture carrier and the sound carrier, these two carriers are beat together and the phase noise cancels out).

A modified old style TV set tuner (not PLL tuned) might work. Set it to channel 6, and move the LO up about 10MHz to get it to tune the FM band, and the tuner's IF output should produce 45MHz FM radio stations.

[bob91343]

The nice thing about prewar FM is the good music on there. No rock, no folk.

[Penthode]

I have a prewar (1941) Stromberg Carlson FM 1025M I regularly use. A good converter is an old TV tuner.

I took a 40MHz video IF video tuner and retuned the channel 6 local oscillator slightly higher to cover the lower end of the FM band. I also sweep aligned the RF stage and Mixer. It works great!

You can get an old tuner from an old TV or VCR. You can also look for a Castle brand tuner/subber on ebay. These were commonly used by TV service men in the 70's and are relatively cheap.

Incidently, the tuner will work pretty well if you just adjust the local oscillator. I did the sweep align to get more distant stations!

Terry

[Jeffhs]

Originally Posted by bob91343

The nice thing about prewar FM is the good music on there. No rock, no folk.

I don't know how you are getting 1930s-era FM stations on a converted console/table set from that period, unless you have a low-power AM transmitter fed by an iPod, etc. and you're receiving the output from it on an AM frequency on your old set. That or else you're joking.

[bob91343]

Originally Posted by Jeffhs

I don't know how you are getting 1930s-era FM stations on a converted console/table set from that period, unless you have a low-power AM transmitter fed by an iPod, etc. and you're receiving the output from it on an AM frequency on your old set. That or else you're joking.

You got it. Just a joke.

[radiodayz]

Originally Posted by bob91343

The nice thing about prewar FM is the good music on there. No rock, no folk.

LOL, yeah, big-band music sounds best on 45 mHz.

[vintagecollect]

hey bgadow, got any pics of your sets please?

[tubesrule]

My 1939 GE HM-80 has the earlier FM band, 39.5-45MHz, and I am able to receive a few strong local FM stations. I suspect this is due to the harmonics in the LO. Because of this I have never got around to making a converter for this set. I also have a pair of Meissner's, a 9-1047 pre-war and a matching 8C post-war. I used to have quite a few more as I collected pre-war FM's at one time, but this is all I have left.

I do have a converter that is shown on the FM Only site here: http://www.somerset.net/arm/fm_only_converters.html
It's down the page a little under the Crystal Devices heading. It is completely passive. I haven't gotten around to trying it either so I don't know if it works, or how well it works.

Darryl

[vintagecollect]

I got my Brewster B-10 to pick up two stations finally, one well.

If someone is going to try TV tuner hack, make sure to have a tuner w/ knobs to know what channel tuner is on. A solid state tuner will work better as I pulled a tuner from a junk portable color tv unit as ---low voltage only needed to power tuner as this is an active setup. An ac adapter at 12 volts dc was perfect. The IF output from vhf tuner goes to FM set's antenna connections. The original VHF antenna flat wires should be saved intact from TV set w/ terminals, this is your new FM antenna connection.

I had an old rca to pin connector adaptor I forgot for my 1930 zenith set which was perfect for audio in. Good volume is achieved. I probaly could get more stations but pick up a 93.7 jazz station on the second harmonic is good enough for me now. I'm just happy on making this functional 1941 FM!

TV tuner actually works on TV ch#4, may have to adjust prewar set as well, TV tuner location touchy, strong stations help and good antenna on VHF terminals.