[600MRG] WIMA capacitors AND substitutes

Sat Jan 13 19:27:03 CST 2018

The Russian amps come and go on eBay.  Careful...some have the devices fitted, some have heat sinks, etc.  I bought a 500 watt water cooled one and a 1KW one with a BIG heat sink.  Just finishing pre-tax info so going to tackle the conversion.

You need to read the Microsemi AN1818:  A 700W Broadband Amplifier Using VRF2944.  Will get you on the right track.

I'm thinking that about all you need to do is change the Ferrite cores.  Best bet seems to be the Laird LFB259128-000 for the big ones.  I'll see if I need to change the input transformer...probably will.

Now for the fun.  I really don't see an easy way to get those matching network off of the boards and back on.  They are wadded in and solder stuck underneath.  Luckily this is LF so I'm just going to put the replacements on a separate board flat so I can easily handle them.  Also will probably use 5 of the 0.1 630V caps as the freq is lower and series Z higher.

The other thing to watch is while the output balun really is just to balance the output on the two units I have and use 50 ohm coax, the two connected to the transistors are wired differently for different impedance transformation.  So the coax according to the ap note should be the geometric mean of the impedances...but I'm not sure so will try to use the coax I'm removing.

Will let you know if I get it done.  N0UU

> On January 13, 2018 at 2:05 PM "D.J.J. Ring, Jr." <n1ea at arrl.net> wrote:
> 
>     Hello,
> 
>     I don't see any previous discussion of the Russian LDMOS amplifiers.
> 
>     Would you post where you ordered one from?
> 
>     I don't know why I can't find the previous thread!
> 
>     Thank you very much,
> 
>     73
> 
>     David N1EA WD2XSH/18
> 
> 
> 
>     On Sat, Jan 6, 2018 at 3:35 PM, lstoskopf at cox.net mailto:lstoskopf at cox.net lstoskopf at cox.net mailto:lstoskopf at cox.net <lstoskopf at cox.net mailto:lstoskopf at cox.net > wrote:
> 
>         > > OK, going to jump back in here.  I've ordered on of the Russian LDMOS 500 watt amps, water cooled.  Saves me from a bunch of mechanical work (have the tools, maybe not the smarts).  Tried to get them to sell me an amp with the Laird LF cores which I have instead of the 43 ones.  Didn't bite.  It should be here next week.  So will pull off the cores and replace with the Laird ones about the same size.  May use twice as many so it might work well at 136 kHz.  3 turns will give 520 ohms X2 at 500 kHz.       They put the blocking caps after the first set to take advantage of the higher Z there and thus lower current.   The schematic they provided shows 3 ea 0.1 uF 630 V caps on each side.  Pulled up the specs on the TDK C4532X7R2J104K230KA chip from DigiKey.  At 500 kHz ESR is 0.05 Ohms, Reactance is a couple of ohms and with 1 A ripple gives a 10C degree temp rise.  (at 136 kHz 0.5A gives the same 10C rise).  500 watts should give about 3A.  They use 3 in parallel on each side for HF so I'm going to use 5 or 6 to keep temps down.  Will let you know how this works out.  http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
> > 
> >         Not planning on running this much, at least until someone comes up with a way to measure EIRP! http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
> > 
> >         N0UU http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
> >         ______________________________ _________________
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> > 
> >     > 
> 