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Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Finished with the initial prototyping for the amp, and it really failed!
The black one uses the TO3 transistors insted of the TO3P because of the heatsinks I had available. The "Finished" amplifier has some real shortcomings. It peaks at 50W rather then 100W like its adjacent prototype. I took some measurements and the PNP Power transistors are not drawing a quiescent current while the NPN's are. If I bias any more, one of the NPN's will open up. So this amp is done. I have had much more luck with the TO3P's with reasonable performance up to 100KHz.
I'm going to start working on something else rather then this thing. I've seen it through to its logical conclusion, which is to dismantle now. Hopefully I can get back on the road with the mos version.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Hazmat.. Type 43 ferrite is ok for rfc and small-signal broadband transformers but the 'Q' at 1 MHz is about 10, and at 12 MHz it's about 1.0 This makes signal transformers less likely to 'ring' BUT at for example 12 MHz the VA = VAR .... i.e. as a PA o/p transformer it will get very hot. e.g. with 'typical' (Inductive reactance) = 4x (load resistance), 40W o/p = 10W core dissipation.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Hi Sulamin,
I've been collecting more information on the subject, including manuals. The trouble is they don't detail their winding ratios for their power combiners or material spec. So for the amp that I'm trying to design here is basically going to be like the ENI 1040L, hopefully more then 100W from 10K to 500K freq. response. In that bandwidth 43 should be okay, but I've been looking at 77 as well. Again, I don't know the turns ratios or core sizes required for the power combiners so this makes my job terribly difficult.
First step right now is get the preamp driver situated. its a quadfilar E-core 77 transformer that will drive the power input stages of the first main PA. The 1040L has multiple PA's in one PA module, and it has 2 of the modules to give it 400W out, so I'm going to start small and hopefully get 2 50W modules going, then see if I can successfully make a power combiner, and go from there.
This ain't easy for me because I never had the benefit of a power electronics course, so I'm a bit slow. I wish I could sit down with the ENI analog designers and take a few classes from them.
So yea, I'm getting some experience with transformers and things, but it is slow.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I started with this stuff about 2 years ago when I got interested in Amateur Radio I'm not 'expert' yet but slowly things become clearer, mainly by experimentation. A good document to start with is the online Fair-Rite catalogue, The most revealing graphs (to me, at my current level of understanding) are the 'Complex permeability vs Frequency graphs. Think of u's as reactive/inductive impedance and u''s as resistive in series.
Starting at page 119 are excellent notes on broadband transformer design.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I was just playing with the transformer coupled amplifier's Preamp and I was able to push it to 20W of drive output, distorted, but it looks fixable. I have to see what I can do on the pre-driver board to cut down the distortion and optimize its bias. The Preamp may need some tweaking too, so we'll see. I wasn't able to use the spec'd parts because I don't have some of that info, but we'll see what I can do here.
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sine wave current booster
