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eHam Forums => Amplifiers => Topic started by: KG4PFO on June 09, 2003, 11:09:41 PM



Title: Converting 10 meter brick to 6 m
Post by: KG4PFO on June 09, 2003, 11:09:41 PM
Shouldnt I be able to convert a 4 pill 10 meter amp (4-sd-1446 pill Good for 6)by simply changing the input transformers to load 6 meters???
Anyone attempted this???
Knowledge wanted.....

Thanks
KG4PFO


Title: Converting 10 meter brick to 6 m
Post by: WB2WIK on June 10, 2003, 01:31:50 PM
Try it!

You need to change more than the "input transformers," as both input and output are critically tuned circuits with power combiners, and none are wideband so they must be replaced with suitable circuits for 50 MHz.

You might need to tweak bypass capacitors and decoupling networks to optimize them for six meters, also, as 28 MHz decoupling is often ineffective at double the frequency and could cause stability problems.

Still, a very worthwhile experiment.

WB2WIK/6


Title: Converting 10 meter brick to 6 m
Post by: W5CEU on June 18, 2003, 12:05:52 AM
I did it! They dont like it though..... 90% of the transistors cut off at 30Mhz and it runs alittle warm also..(look up the spec's at RF parts.com "MRF-455" etc.) I changed the transformer turns and a RF choke and tweeked the variable caps a bit.I get about half the rated power It still wakes up my little MFJ! ,most CB type amps are way over rated any how.I'd say use it for 10m and find a old sweep tube amp to mod.73's


Title: Converting 10 meter brick to 6 m
Post by: N4GI on June 18, 2003, 11:17:23 AM
Don't do it.  Those cheap "10meter" CB amps are nothing more than non-FCC-approved-dirty-hash-boxes spewing garbage about the airwaves.  

It's bad enough they are used to trash 10meters, 6meters can surely do without them - help keep the ham bands clean.

73,
Blake N4GI  


Title: Converting 10 meter brick to 6 m
Post by: KG4PFO on July 07, 2003, 08:12:37 PM
It wont spew emissions if you run filters, that would be the smart "and legal" thing to do.

KG4PFO


Title: Converting 10 meter brick to 6 m
Post by: N6OTQ on July 11, 2003, 10:56:27 AM
The SD1446 is rated to 50 MHz.  Please see
   < http://us.st.com/stonline/books/ascii/docs/2805.htm >

and disregard the previous "30 MHz cutoff" remark.  In general, RF transistors are specified with a cutoff frequency by the manufacturer because they begin to lose gain and exhibit other undesired effects like parasitic oscillation and unpredictable internal filtering effects based on stray inductance and capacitance of the internal structures.

The input and output transformers that worked from 80 to 10 meters probably will give you another half-octave of bandwidth, but there are capacitors on the input and output of those transformers that need to be reduced in value.  These capacitors serve to minimize the gain variance of the amp over frequency -- in a general sense, for SS amps, gain and frequency are inversely related.  A conversion should be simple and effective.  The trade off is that the lower frequency capability of the amp -- 80 meters -- will be lost.

I urge you NOT to just hook the amp to a 6M exciter to "see what happens" -- it might work, but it might also blow up.  You'd be much better off to attempt a modification, or trade the amp, or sell it and buy a dedicated 6M amp.  

None of us here have any illusions about what a "10 meter 4-pill brick" amplifier can be used for.  I hope I speak for everybody here when I express my personal feelings that the amplifier be kept in amateur service and used only in the ham bands, rather than selling it to someone who might misuse it.  Our best course of action is to convert CB equipment AND operators to legal radios and law-abiding ham radio operators.

Jim N6OTQ

PS -- the SD1446 is rated at 183 W max dissipation per device, and spec-ed at 55% efficiency.  So if this were used as a "disposable" amplifier, it could deliver somewhere around 800 watts in high-duty-cycle SSB in Class C.  We all know what that service is in the real world.

If you are clueless, it'll swing 1200+ on a Dosy.