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Old Oct 19, 2005, 02:26 PM
Robots... robots everywhere
minifly's Avatar
Cape Town, South Africa
Joined Jan 2003
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Help!
Main output transistor on TX burnt out -- C4735 equivalent?

It seems that I have burnt out the main output transistor on my JR-X378 TX, and was wondering if there is an equivalent, (preferably something that runs a bit cooler ) for the C4735.
I have looked around and cannot find it at any of my local dealers.

I would send it back to JR, but have passed my warrenty, so i have nothing to lose.

Please remember that I live in South Africa, this is a 35mHz tx

Thanks,
Minifly
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Old Oct 19, 2005, 03:19 PM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
2,505 Posts
Here's the data sheet. No NTE.

Here for $1.99 ea..

Gary
--
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Last edited by Gary Warner; Oct 19, 2005 at 03:27 PM.
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Old Oct 19, 2005, 06:51 PM
Registered User
Switzerland
Joined Sep 2005
66 Posts
try 2N4012, 2N3866, 2N4427

But don't blame me if they get hot! to avoid this check out their datasheets and compare the currents and powers.

If you have a CB Radio you could also rob its transistor (or see what type it is), as the 2sc4735 is a standard CB PA transistor.

diego
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Old Oct 19, 2005, 07:34 PM
Registered User
Switzerland
Joined Sep 2005
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2SC2078 is such a cb transistor.

have you a cb repairshop near you? maybe they will sell you one?!!
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Old Oct 20, 2005, 04:08 AM
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East Anglia, UK
Joined Sep 2002
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Be brutal - my first 27Mhz tranny that WORKED cranked out about 3.5 watts with a BFY51 - able, in its metal can, to do it without cooking...

Within limits any NPN silicon RF transitsor will WORK with a bit of a retune ...maybe more, or less, powerfully..and efficiently.
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Old Oct 20, 2005, 07:13 AM
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minifly's Avatar
Cape Town, South Africa
Joined Jan 2003
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decided to go with 2N3866, due to availability and another recommendation by email.

i will tell you how it goes, thanks for now
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Old Oct 21, 2005, 06:05 AM
dieselburner
andrew b's Avatar
Wyke, Bradford, west yorks
Joined Mar 2005
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Quote:
Originally Posted by vintage1
Be brutal - my first 27Mhz tranny that WORKED cranked out about 3.5 watts with a BFY51 - able, in its metal can, to do it without cooking...
The BFY series were great, I used them for RF power and for medium current switching (relays), I "rescued" my supply of BFY's from the CRT base of early color TV's where they served the purpose of color drives.
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Old Oct 21, 2005, 07:20 AM
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Acetronics's Avatar
Le Treport, France
Joined Jun 2004
1,408 Posts
Hi, Minifly

European Classics are ( output power order ) : 2N2219A , 2N 4427, 2N 3866 , 2N 3553 , 2N 3375

Note a BD 137 works great too ... ( yes, yes ... try it before laughing !!! )

Alain
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Old Oct 21, 2005, 12:50 PM
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North East England UK
Joined Jan 2003
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Minifly,
As you live in SA, have you tried Maplins...?

( I lived there some 20 yrs ago and they were just dipping their toes in the water...they have since established various branches...)

If Maplins fail you, where are you in SA...? I recall there were a few electronics suppliers in J'berg......


Ah Cape Town........
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Old Oct 21, 2005, 01:28 PM
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minifly's Avatar
Cape Town, South Africa
Joined Jan 2003
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I got the 2n3688 from communica, installed, and everything is working fine now

The current limiting resistor is 3.2 ohm, if i put a heat sink in would it be safe to use a 2.2 ohmm one instead? I know that the range would be increased alot, but would this cause any problems with stuff like harmonics and interference for other people on adjacent channels?
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Old Oct 21, 2005, 01:48 PM
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Bridgwater, UK
Joined May 2003
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I used a BD139 on mine.

Terry
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Old Oct 21, 2005, 02:39 PM
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MAVA's Avatar
El Dorado Hills, California, U.S.A.
Joined Mar 2000
548 Posts
Minifly,

In my old Ace Radio had the similar problem, All I did is replaced the trasistor with the original got the RF deck re-tuned and added a heatsink with thermal (add very little so it looks transparent-more compond is worse)compond.

No problems since that happend..

Martin
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Old Oct 21, 2005, 04:35 PM
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minifly's Avatar
Cape Town, South Africa
Joined Jan 2003
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chippie,
maplins has been bought out by yebo electronics ( http://www.fort777.co.za ) and they were the first people i checked. after that i checked communica, and they only had the 2n3866, so i went with that
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Old Oct 21, 2005, 04:49 PM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
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I used the 2N3866 as a final o/p on transmitters at 144mHz, it gave at least a Watt so it should be more than adequate for 35MHz RC.

Andy.
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Old Oct 22, 2005, 04:10 PM
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minifly's Avatar
Cape Town, South Africa
Joined Jan 2003
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well, i tried the 2.2 ohm and suddenly things started going wrong: the 2n3688 started REALLY heating up, and my range went way down as well.

at first i thought that the circuit was just out of tune, so i fiddled with the pot and coil, but the range was still WAY worse than before (even worse than with the old 2sc4735 burnt out). I put the 3.2 ohm back, and everything is great again. Maybe the gate is drawing too much and distorting the signal? Or I'm out of the linear curve of the 2n3866 and peaked it out/got a bit too close the the peak, and into part of the non-linear curve?

anyway, everything is fine, and i'm up and running again.

Thanks to all who contributed.
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