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

I own a pair of the prewar Philco sets (a table model and a console) but have not tackled either as of yet. I also have a Stromberg-Carlson which is waiting in line.

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. :D

You got it. Just a joke.

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

hey bgadow, got any pics of your sets please?

:thmbsp:

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

project is complete! 1941 Prewar FM
 

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.
:banana:

I have recently been able to pick several stations with a complex combination of tv tuner and dial settings. This setup isn't real feasible unless doing a radio log. It's great to see set pick up several stations. I'm now motivated to make the other converter for better results to cover more of the FM band. There's two versions of the converter shown, a breadboard and a finished point to point solder on a chassis, I guess the later for better selectivity and sensitivity.

If someone tries tv tuner hack, I found moving the FM antenna now to one of tv tuners terminals on top gives best sensitivity. This helped afer changing the delicate shielded cable for IF output of TV tuner to sturdier two wire setup. This caused Brewster tuner to be detuned and tune at new location at 50.5 still receiving well.

Someone needs patience with tv tuner setup, antenna lead position and location, along w/ TV tuner has effect. When changing something as above could detune circuits a little as higher freqs.

Here is my Stromberg Carlson set. It appears that Stromberg Carlson and GE were the first manufacturers to go ito FM in a big way. Stromberg Carlson launched an FM receiver in 1939, one year before FCC FM commercialization.

With the TV tuner set to channel 6 and the local oscillator adjusted upward, The radio will receive 88 MHz to 96 MHz corresponding to 50 MHz to 42 MHz on the old band. Note I reversed the old band from 50 to 42. This is because the TV tuner oscillator is set to 138 MHz. This is how it is calculated:

Channel 6 local oscillator = 87.25 MHz(ch6 snd) + 41.25 MHz (TV snd I.F.) = 128.5 MHz

Low Band FM converter osc. = 88MHz (new band low end) + 50MHz (old band high end) = 138 MHz

Further: Converter osc. = 96MHz (new band 88 + (50-42)) + 42 MHz (old band low end) = 138 MHz.

What this means is that with the local oscillator in the tuner adjusted 9.5 MHz higher to 138 MHz, the old band FM radio will receive the low end of the new band. It must be noted that the old band was 8MHz wide and the new band is 20 MHz wide, so that only a portion of the band is covered with one TV tuner channel setting. It follows that if you can rebuild the tuner to cover the entire band with three separate channel selections of the tuner, each with a progressively higher local oscillator setting. Eg 138 MHz osc. for 96 to 88 MHz, 146 MHz for 104 to 96MHz and 154 MHz for 112 to 104 MHz. Or else you can over lap. Then again you may be able to get the fine tuning control of the tuner give you extra range.

Note that I have also adjusted the TV tuner RF stages for the FM radio band. In that way you can receive more distant stations. I find with the TV tuner, the old Stromberg Carlson can receive distant stations as well as a new FM radio.

Note the inverted calibration. This is because when the local oscillator freq. is set above the incoming signal freq. the RF frquencies are inverted. Recall with analog TV, the broadcast video carrier frequency is lower than the broadcast Sound carrier frequency. The higher local oscillator inverts the arrangement in the video IF.

I hope this helps.

Cheers,

Terry

The "Converters from Magazine Articles" section of this link includes a 1 tube [6J5] and a 1N34 crystal diode converter by Harvey Keys I want to build for my Dad's Philco Console from 1940. It appears simple and the article has good instructions.
Film@Eleven

Cliff

Mystery FM bands
 

I will start a new thread but I do not understand the TWO bands these 1947 sets have. I know one is 42-50 MC, but with channel numbers instead.
The Stromberg Carlson 1210-PL is the pretty one. The other one I only have the chassis, stamped "model 1121" and cannot ID. Any ideas?
Dave 63

Perhaps those sets were meant to tune the TV FM sound carier. :scratch2:

The 200 to 300 is the current 88 to 108 FM band. Those were the assigned channel numbers (which are still assigned to stations). I have a Meissner FM tuner that has both the frequency and the channel numbers for the modern band.

Why channelize radio?

Does that mean these had both old and new FM bands? I had the StrombergCarlson for 32 years. I had it working then and it did get a few FM stations on the 200-300 band as I recall. I left the tuner at 102.5 FM as photo shows. BTW, I had an early mobile receiver that did receive a nearby TV's leaky sound carrier on 41.25 MC.

Thanks!
Dave 63

It appears so. The first one should tune 88-108Mc on the 201-299 band and 42-50Mc on the 21-99 band (42.1 to 49.9Mc). The Stromberg Carlson radio would tune 88-108Mc on the 200-300 band and 42-50Mc on the 20-100 band (I would assume 42.0 to 51.0Mc).

BTW, the first photo is also a Stromberg Carlson:

http://www.radioatticarchives.com/radio.htm?radio=3198

Two FM Bands here
 

Can anybody ID the chassis in attached photos?

The pretty one is a Stromberg Carlson 1210PL, also with both new and old bands....odd.

Dave 63

See the link in my post above. The chassis is from a Stromberg Carlson model 1121.

Some transitional post-WW II better sets had both FM bands. Zenith made quite a few old band-current FM band sets.

Thanks sean, I am getting loopy trying to use this site. Paging ahead helps.

I thought I was the only nut who would save an orphan chassis before I discovered it.

Dave 63
Now looking for FM48 with a 11-foot dipole..haha

FOUND it, the easiest converter!!!!!!!!!
 

Someone HERE build this and try, I'm going to in nnext week or so. My brewster is just sitting collecting dust.

EASIEST converter, Only one crystal detector. If someone builds this, please state here specific values fo trimmer caps used.

link

http://books.google.ru/books?id=zt4D...nverter&f=true

I built the convereter last day and it works like a charm, much more stable than TV tuner hack. Very stable with strong -- loud signal on 93.7 KJZY Station. Problem is, on picks up this one station only. Other stations just heard as modulation hum, any suggestios? Anyone familiar w/ prewar FM's , Please PM me! Will a signal booster work? I believe this to be strongest FM station, only tunes to this anyways? How many statios can anyone tunes w/ theirs using a conveter? Any tips? :scratch2:

Hello kent, I had a 1948? zenith console ol new band fm radio, Got rid of it. Should of kept it, needed reveneering, Zenith did ultra cheap photo veneer finish. Spin a record once in a while, had record player so was'nt teribly attached. Radio would of been worth saving if cabinet totally gone thru. Relized afterwards those radios not very common as early Fm.

:thmbsp::music:

Anybody figure out how to download page 233 with the convertor article on it? Doesn't seem possible to me.

In the meantime, you can buy a 'Sentry' HO 900 FM wireless headset system on eBay for ~$20 that transmits in the 42 to 50 MHZ band, crystal controlled and sounds good when playing a cd through it. It works great through my Philco 42-395 console.

Cliff

Some older (late '40s) Zenith radios also tuned AM and both FM bands, although the old FM scale on these sets was actually calibrated in MHz (mc) rather than channel numbers on that range. The radios I'm thinking of are the old Zeniths with the arc-shaped tuning dials and the ones with round dials and a "Tone Register" tone control system. I am guessing the latter were made in the late '40s as well, owing to the presence of the old 40-MHz FM band which was eliminated from all Zenith, et al. FM radios after all FM broadcasting transitioned to 88-108 MHz by 1949 or thereabouts.

There may be next to nothing to hear on the old 42-50 Mc. band today, although I suppose one could overhear old cordless telephones which operated on the old 46-49 MHz range if such are still in existence nowadays, which I doubt -- all current cordless telephones now operate in the GHz [gigahertz] range. Most of the old 46-49MHz cordless phones have probably been scrapped, due to being forced into obsolescence by the new 5.8 GHz phones now in use.

You can buy "win" a 'Sentry' HO 900 FM wireless headset system on eBay for ~$20 that transmits in the 42 to 50 MHZ band, crystal controlled and sounds very good when playing a cd through it.

It works great through my Philco 42-395 console.

Cliff