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[Neil]

Some time ago I WAS asked to dispose of some RC model boats and some RC GEAR by the widow of an old friend of mine.
The models went to the Blackpool show about 4 years ago as did the radio gear..........however all the radio gear was of American US bought electronics and therefore no good or legal [so I was told] and so were virtually given away.
However whilst rummaging through all my RC gear to match up a tx to an rx for my little Liverpool lifeboat I found an American bought receiver of 75mhz that had missed the bag 4 years ago.

Would it be able to be changed to 40mhz as it looks brand new and IS a Futaba 4 channel, which if able to be would come in very handy as I run 40 meg as 2.4ghz sets WON'T work on my lifeboats which usually sail on salt water with the radio gear always stowed deep in the grp or wooden hulls where 2.4ghz won't penetrate.

If it was feazible I would like something that an old friend had in a round about way had given me........I'm soft and nostalgig that way, lol

   

[dodgy geezer]

While it is 'possible' to do anything, it would be highly impractical to convert the rf section of a receiver from 75 to 40. You would need to extensively change things - effectively build a new rf section, and would need considerable design knowledge to do so. Even changing from 35 to 40 can require component changes.


You have the original rx as a keepsake. Why not just pick up a 40 rx from ebay?

[Neil]

Thanks for that and appreciate the info.........as i can hardly wire in a 3 pin plug your suggestion of just keeping it as a keepsake is the best idea.
lets face it, a 40mhz rc on ebay is cheep as chips anyway, but i think i'll go and buy a new one from componant shop.

again, many thanks for the help. appreciate it.

cheers. neil

[roycv]

Hi Dodgy, Putting a 40Mhtz crystal into a 35Mhtz RC set works without problem.  No component changes needed. 
I bought a Fleet  Plainsman direct from Fleet runs on 40Mhtz.  A while later I found a label on the bottom saying it was certified 35Mhtz!

I have since bought 3 off 35 Mhtz sets when they were cheap and these run on 40 mhtz crystals.  Never found any of the double.... type 40Mhtz crystals so the rx. was discarded as I have a dozen 5 ch 40Mhtz rx's.

Converting from 70 Mhtz will require component cahnges as you said.

Roy

[dodgy geezer]

Hi Dodgy, Putting a 40Mhtz crystal into a 35Mhtz RC set works without problem.  No component changes needed. 
I bought a Fleet  Plainsman direct from Fleet runs on 40Mhtz.  A while later I found a label on the bottom saying it was certified 35Mhtz!

I have since bought 3 off 35 Mhtz sets when they were cheap and these run on 40 mhtz crystals.  Never found any of the double.... type 40Mhtz crystals so the rx. was discarded as I have a dozen 5 ch 40Mhtz rx's.

Converting from 70 Mhtz will require component cahnges as you said.

Roy

Yes - I understand that it can be possible, though I have tried it and failed. I note that in some of the design documentation I have for home kits there are some component differences between the 35 and 40 versions. I suspect that in some cases designers make the carrier tuning fairly broad and use the same circuit for both frequencies - others may opt for precise tuning and need different circuits.   

While 35 and 40 are quite close and similar circuits/components will resonate around these frequencies. by the time we get up to 75 you are going to need a redesign...

[roycv]

Hi Dodgy from memory I remember that there is only a 10 or 20 picofarad change in the RF circuit.  As long as the crystal hits the resonant circuit before it completes a cycle then the RF can adjust to a different frequency.

I recall a professional saying that all imported 40 Mhtz sets in use in the UK, come in as 35Mhtz.  I know that Fleet boasted of being all UK.
Fleet is good reliable equipment but he just had to be a bit different!

Roy
 

[dodgy geezer]

Micron also required a retune of an IF coil and a resistor/cap pair replacing. Not a lot, as you say, and some Rxs were obviously designed to do both frequencies. But  75 is a bit far away.


It MIGHT be possible to convert it with some comparitively minor alterations - but the work required to find this out would be non-trivial on its own...

[roycv]

Hi Dodgy, I built one of the 7 ch. Micron kits (Tx and rx) when we all used 27Mhtz and of course this was FM. 
It went together well, and I built 3 of his rx's which I still prefer to the Futaba ones of the time.  I bought a couple of the now standard sockets and substituted them for old connectors to fit current servos which are still in occasional use.
I think I fitted nearly all of his 'extras' or at least they could be plugged in, a lovely set.

Roy