MRF477 in a Hygain V

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Rob_RS2000
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MRF477 in a Hygain V

Postby Rob_RS2000 » 04 Jan 2017, 15:35

Hi all, this is my first post on here I have been reading with interest for a while.
I am returning to the hobby after a 15 year break and am looking for some advice.

I picked up a Hygain V, 4 blocks of 50 version (PTBM125A4X). The final (2SC1969) has blown on it and I was going to try and repair with spares that I have lying around. The only good output transistor that I can find is a MRF477 from a dead Lincoln.

I did read on here somewhere that this can be used to replace a 2SC1969 but wondered what other mods are required to make this work. I have searched but guess it is not a common mod due to the MRF477 being expensive.

Any help would be appreciated, thanks in advance.
Rob.

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Re: MRF477 in a Hygain V

Postby dt307 » 04 Jan 2017, 18:28

pin outs are different so its not a direct swap you would have to cross the legs.
im sure if you posted in the wanted section some one would be more than willing to swap you a 1969 or a 2312 for your mrf.
if you do require the info to put it in i will give it but you need to add some caps as well.
and the cybernet chassis can just cope with the biasing of a 1969 let alone the 477 would be interesting.
it may work great no idea as i have never done what your asking. i take out the mrf in all lincolns that pass this way and put in a 1945 and it works better for me but not for others

should add without the test equipment fitting the totally wrong transistor in a circuit that wasnt designed for it might work fine but you wont know how dirty the transmission is (but i used a 455 and a 1446 total mismatch in a b300p for years)
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Re: MRF477 in a Hygain V

Postby Otter » 04 Jan 2017, 22:41

Surely it would be better to replace the final with an IRF520N MOSFET, at least we know that conversion works. https://www.youtube.com/watch?v=rXVVptMcFpw
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Re: MRF477 in a Hygain V

Postby The Collector » 08 Jan 2017, 15:05

How do you test a 2SC1969?

I've got one that I was told worked, but have no way of knowing.
Apart from testing continuity or 12v, I'm pretty bloomin' useless with a multimeter ;)

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Re: MRF477 in a Hygain V

Postby dt307 » 08 Jan 2017, 16:32

The Collector wrote:How do you test a 2SC1969?

I've got one that I was told worked, but have no way of knowing.
Apart from testing continuity or 12v, I'm pretty bloomin' useless with a multimeter ;)


http://www.elexp.com/electrical_measure ... art_3.aspx

or check none of the pins are a direct short 0 ohms to each other and wack it in ... remember smoke is NOT good....honestly :D
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Re: MRF477 in a Hygain V

Postby The Collector » 08 Jan 2017, 20:15

I looked briefly at that link and discovered what dyslexia must be like to sufferers! ;) All the words blended into each other and other words didn't even look like words and the pictures were missing but thanks anyway.
I'll stick to soldering 4-pin mic' plugs (just about).

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Re: MRF477 in a Hygain V

Postby Rob_RS2000 » 08 Jan 2017, 22:34

Thanks for the advise guys, think I will go with the IRF520N MOSFET.

I have decided to repair the Lincoln, the problem is that the MPU is no good, so I am going to replace with a PIC, I have got most of the code sorted

Otter,
I have read in other threads that you have PIC controlled Lincoln and was wondering if you can give me any pointers on the LCD. I am using a PICAXE for prototyping and have found some code to control upd7225 type display drivers. I am not having much success with this code and beginning to think that I may have a faulty display.
Thanks
Rob.

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Re: MRF477 in a Hygain V

Postby Rob_RS2000 » 09 Jan 2017, 22:41

Just a quick update on the Lincoln, I now have all digits working along with decimal points and frequency change markers, the markers are effectivly decimal points for the digits with no dp.
Still can't work out (TX, RF, MOD, SWR & Cal arrow).

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Re: MRF477 in a Hygain V

Postby Rob_RS2000 » 17 Jan 2017, 10:22

Ok, I have got hold of some IRF520N MOSFETs and 50K presets but can't find the companion part for sale anywhere.

Is there a circuit that I can construct myself to set the biasing?

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Re: MRF477 in a Hygain V

Postby bigal68 » 17 Jan 2017, 11:15

Can't remember which one.....

But if you check out SWIZZRADIO's youtube channel, he does the mosfet change on some cybernets I think, and he shows the circuit diagrams for the various companion parts....
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Re: MRF477 in a Hygain V

Postby JollyRoger » 17 Jan 2017, 11:37

Rob_RS2000 wrote:Ok, I have got hold of some IRF520N MOSFETs and 50K presets but can't find the companion part for sale anywhere.

Is there a circuit that I can construct myself to set the biasing?


And the preset Im sure is 500K not 50K
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Re: MRF477 in a Hygain V

Postby Rob_RS2000 » 18 Jan 2017, 13:11

Ok, so I have fitted the IRF520n but when in TX the 9.4v rail drops to 4v at AVR Q36?

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Re: MRF477 in a Hygain V

Postby dt307 » 18 Jan 2017, 17:11

goto you tube Mark Wiesel66 has a good video showing exactly what to do to a cybernet chassis
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Re: MRF477 in a Hygain V

Postby Otter » 18 Jan 2017, 17:40

I'd copy the output of the SS158EDX - forget about the companion parts. Make sure the drain of the IRF520 is connected to where the collector of the 2SC1969 was, and the gate is where the base was. These pins are swapped compared to the 2SC1969. Emitter and source are in the same position (GND). Run the FET bias from the regulated rail, and set the gate voltage for 50mA quiescent current with no modulation in SSB mode.
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