Possible to convert 42MC-50MC FM?
 

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.

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.

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.

thanks to all
 

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!!!

:thmbsp::yes:

Found the info, Thanks!!!

:banana:

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

found plans, etc. link
 

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.

:banana:

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.

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.

http://www.wa2ise.com/radios/em460.jpg

Update on block conversion of 100MHz FM to 45MHz
 

Tried the same thing with an old VCR, and got much better results. Its local oscillator must be much quieter, as converted FM radio stations fed to the 45MHz FM set sounds a lot better. I connected a special output (via a 470pf high voltage cap) jack to a coax cable that connects to a special port on the VCR's tuner module (probably intended to feed a stereo TV IF amp, filter and demodulator). You want to be in front of the video IF filter, but just after the mixer stage of the tuner. This feeds the 45MHz FM prewar radio. One has to set the VCR to tune CATV channels, and then tune in channels 95, 96 or 97, depending on which segment of the 100MHz FM band you want to block convert. WSBS-FM, 101.1 comes in at about 47.7 with the VCR set to cable channel 97. Or about 41.7 on channel 96. WAXQ 104.3 comes in at about 44.5 on channel 97. Note that the order of stations will be flipped as you tune up the 45MHz FM dial.

You can also pick up the weather reports transmitted around 182MHz at about 46.5Mhz when setting the VCR to cable channel 21. And around that for fire and police, all these will be at much reduced volume as they are narrow band FM.
The VCR is an RCA model VR657HF.

That VCR converter is interesting, I'm going to build that compact DIY converter , will update on results later. I'm interested in DIY as can be put in a small box and tucked behind my Brewster tuner set. Your posts are good W2ISE, PLEASE REPLY TO pm.

It appears there was a lot of interest in early FM 15 to 20 years ago. Several old articles done including the well laid out one I mentioned. Not too much as of recently? Perhaps more of an old timers wanting to rig these for use. Never heard anyone using a prewar restored fm radio.

ONLY saw one at old friends house 8 years ago, he has since passed away. The power transformer was bad as I checked it for him 20 years ago. It sat in their living room as a fine piece of furniture as had fancy cabinet with matching burl grain doors. I remember wanting to see set run, knowing the FM was probaly obsolete. Had weird ultra futuristic gray plastic and metallic knobs and look of benzel. Made radio look more like a 50s or late s 50s set. Definetely 1941, had only obsolete band, saw ad for exact set somewhere in Life magazine- full page.

Have since early FM interests me. These sets must of been rare in general. Most must of been scrapped. Pic of Brewster tuner set restored by someone as older project. original cabinet in very good shape which doesn't show age of 70 years.

if anyone else using prewar fm please post pics!

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

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

If anybody should need them, I have a few VHF tuners from about 1950-52 which are looking for a home. 2 of them are Emersons, not sure about the other one. Yours for shipping.

Hey pentode, please post a pic of your 1025M PLEASE

thanks for tip pentode. What channel covers the other end of fm dial, channel 7?

Can eveyone who has a prewar set chime in please, especially if in use

I have a Philco 42-1015 that I am trying to get finished up that I intend to use somewhat regularly (pre-restoration photo below). I have a place in the living room ready for it anyway. I built a converter based on the Hallicrafters CN-1 converter. I am looking for a table model 1942 Philco with FM and I thought about designing a solid state converter loosely based on the CN-1 for that.

http://www.antiqueradios.com/gallery...2_1015_2sm.jpg